safety ci
[physik/posic.git] / moldyn.c
index f09c93a..c25fed3 100644 (file)
--- a/moldyn.c
+++ b/moldyn.c
 
 #include "moldyn.h"
 
-#include "math/math.h"
-#include "init/init.h"
-#include "random/random.h"
-#include "visual/visual.h"
-#include "list/list.h"
-
-
 int moldyn_init(t_moldyn *moldyn,int argc,char **argv) {
 
-       //int ret;
-
-       //ret=moldyn_parse_argv(moldyn,argc,argv);
-       //if(ret<0) return ret;
-
        memset(moldyn,0,sizeof(t_moldyn));
 
        rand_init(&(moldyn->random),NULL,1);
@@ -78,6 +66,13 @@ int set_temperature(t_moldyn *moldyn,double t_ref) {
        return 0;
 }
 
+int set_pressure(t_moldyn *moldyn,double p_ref) {
+
+       moldyn->p_ref=p_ref;
+
+       return 0;
+}
+
 int set_pt_scale(t_moldyn *moldyn,u8 ptype,double ptc,u8 ttype,double ttc) {
 
        moldyn->pt_scale=(ptype|ttype);
@@ -93,12 +88,21 @@ int set_dim(t_moldyn *moldyn,double x,double y,double z,u8 visualize) {
        moldyn->dim.y=y;
        moldyn->dim.z=z;
 
+       moldyn->volume=x*y*z;
+
        if(visualize) {
                moldyn->vis.dim.x=x;
                moldyn->vis.dim.y=y;
                moldyn->vis.dim.z=z;
        }
 
+       printf("[moldyn] dimensions in A and A^3 respectively:\n");
+       printf("  x: %f\n",moldyn->dim.x);
+       printf("  y: %f\n",moldyn->dim.y);
+       printf("  z: %f\n",moldyn->dim.z);
+       printf("  volume: %f\n",moldyn->volume);
+       printf("  visualize simulation box: %s\n",visualize?"on":"off");
+
        return 0;
 }
 
@@ -155,38 +159,56 @@ int set_potential3b(t_moldyn *moldyn,pf_func3b func,void *params) {
        return 0;
 }
 
-int moldyn_set_log(t_moldyn *moldyn,u8 type,char *fb,int timer) {
+int moldyn_set_log_dir(t_moldyn *moldyn,char *dir) {
+
+       strncpy(moldyn->vlsdir,dir,127);
+
+       return 0;
+}
+       
+int moldyn_set_log(t_moldyn *moldyn,u8 type,int timer) {
+
+       char filename[128];
+       int ret;
 
        switch(type) {
                case LOG_TOTAL_ENERGY:
                        moldyn->ewrite=timer;
-                       moldyn->efd=open(fb,O_WRONLY|O_CREAT|O_TRUNC);
+                       snprintf(filename,127,"%s/energy",moldyn->vlsdir);
+                       moldyn->efd=open(filename,
+                                        O_WRONLY|O_CREAT|O_EXCL,
+                                        S_IRUSR|S_IWUSR);
                        if(moldyn->efd<0) {
-                               perror("[moldyn] efd open");
+                               perror("[moldyn] energy log fd open");
                                return moldyn->efd;
                        }
                        dprintf(moldyn->efd,"# total energy log file\n");
                        break;
                case LOG_TOTAL_MOMENTUM:
                        moldyn->mwrite=timer;
-                       moldyn->mfd=open(fb,O_WRONLY|O_CREAT|O_TRUNC);
+                       snprintf(filename,127,"%s/momentum",moldyn->vlsdir);
+                       moldyn->mfd=open(filename,
+                                        O_WRONLY|O_CREAT|O_EXCL,
+                                        S_IRUSR|S_IWUSR);
                        if(moldyn->mfd<0) {
-                               perror("[moldyn] mfd open");
+                               perror("[moldyn] momentum log fd open");
                                return moldyn->mfd;
                        }
                        dprintf(moldyn->efd,"# total momentum log file\n");
                        break;
                case SAVE_STEP:
                        moldyn->swrite=timer;
-                       strncpy(moldyn->sfb,fb,63);
                        break;
                case VISUAL_STEP:
                        moldyn->vwrite=timer;
-                       strncpy(moldyn->vfb,fb,63);
-                       visual_init(&(moldyn->vis),fb);
+                       ret=visual_init(&(moldyn->vis),moldyn->vlsdir);
+                       if(ret<0) {
+                               printf("[moldyn] visual init failure\n");
+                               return ret;
+                       }
                        break;
                default:
-                       printf("unknown log mechanism: %02x\n",type);
+                       printf("[moldyn] unknown log mechanism: %02x\n",type);
                        return -1;
        }
 
@@ -203,6 +225,10 @@ int moldyn_log_shutdown(t_moldyn *moldyn) {
        return 0;
 }
 
+/*
+ * creating lattice functions
+ */
+
 int create_lattice(t_moldyn *moldyn,u8 type,double lc,int element,double mass,
                    u8 attr,u8 bnum,int a,int b,int c) {
 
@@ -212,10 +238,11 @@ int create_lattice(t_moldyn *moldyn,u8 type,double lc,int element,double mass,
 
        count=a*b*c;
 
+       /* how many atoms do we expect */
        if(type==FCC) count*=4;
-
        if(type==DIAMOND) count*=8;
 
+       /* allocate space for atoms */
        moldyn->atom=malloc(count*sizeof(t_atom));
        if(moldyn->atom==NULL) {
                perror("malloc (atoms)");
@@ -238,9 +265,10 @@ int create_lattice(t_moldyn *moldyn,u8 type,double lc,int element,double mass,
 
        /* debug */
        if(ret!=count) {
-               printf("ok, there is something wrong ...\n");
-               printf("calculated -> %d atoms\n",count);
-               printf("created -> %d atoms\n",ret);
+               printf("[moldyn] creating lattice failed\n");
+               printf("  amount of atoms\n");
+               printf("  - expected: %d\n",count);
+               printf("  - created: %d\n",ret);
                return -1;
        }
 
@@ -256,10 +284,93 @@ int create_lattice(t_moldyn *moldyn,u8 type,double lc,int element,double mass,
                check_per_bound(moldyn,&(moldyn->atom[count].r));
        }
 
-
        return ret;
 }
 
+/* fcc lattice init */
+int fcc_init(int a,int b,int c,double lc,t_atom *atom,t_3dvec *origin) {
+
+       int count;
+       int i,j;
+       t_3dvec o,r,n;
+       t_3dvec basis[3];
+       double help[3];
+       double x,y,z;
+
+       x=a*lc;
+       y=b*lc;
+       z=c*lc;
+
+       if(origin) v3_copy(&o,origin);
+       else v3_zero(&o);
+
+       /* construct the basis */
+       for(i=0;i<3;i++) {
+               for(j=0;j<3;j++) {
+                       if(i!=j) help[j]=0.5*lc;
+                       else help[j]=.0;
+               }
+               v3_set(&basis[i],help);
+       }
+
+       v3_zero(&r);
+       count=0;
+       
+       /* fill up the room */
+       r.x=o.x;
+       while(r.x<x) {
+               r.y=o.y;
+               while(r.y<y) {
+                       r.z=o.z;
+                       while(r.z<z) {
+                               v3_copy(&(atom[count].r),&r);
+                               atom[count].element=1;
+                               count+=1;
+                               for(i=0;i<3;i++) {
+                                       v3_add(&n,&r,&basis[i]);
+                                       if((n.x<x+o.x)&&
+                                          (n.y<y+o.y)&&
+                                          (n.z<z+o.z)) {
+                                               v3_copy(&(atom[count].r),&n);
+                                               count+=1;
+                                       }
+                               }
+                               r.z+=lc;        
+                       }
+                       r.y+=lc;
+               }
+               r.x+=lc;
+       }
+
+       /* coordinate transformation */
+       help[0]=x/2.0;
+       help[1]=y/2.0;
+       help[2]=z/2.0;
+       v3_set(&n,help);
+       for(i=0;i<count;i++)
+               v3_sub(&(atom[i].r),&(atom[i].r),&n);
+               
+       return count;
+}
+
+int diamond_init(int a,int b,int c,double lc,t_atom *atom,t_3dvec *origin) {
+
+       int count;
+       t_3dvec o;
+
+       count=fcc_init(a,b,c,lc,atom,origin);
+
+       o.x=0.25*lc;
+       o.y=0.25*lc;
+       o.z=0.25*lc;
+
+       if(origin) v3_add(&o,&o,origin);
+
+       count+=fcc_init(a,b,c,lc,&atom[count],&o);
+
+       return count;
+}
+
 int add_atom(t_moldyn *moldyn,int element,double mass,u8 bnum,u8 attr,
              t_3dvec *r,t_3dvec *v) {
 
@@ -365,14 +476,16 @@ int scale_velocity(t_moldyn *moldyn,u8 equi_init) {
                        count+=1;
                }
        }
-       if(count!=0) moldyn->t=(2.0*e)/(3.0*count*K_BOLTZMANN);
+       if(count!=0) moldyn->t=e/(1.5*count*K_BOLTZMANN);
        else return 0;  /* no atoms involved in scaling! */
        
        /* (temporary) hack for e,t = 0 */
        if(e==0.0) {
        moldyn->t=0.0;
-               if(moldyn->t_ref!=0.0)
+               if(moldyn->t_ref!=0.0) {
                        thermal_init(moldyn,equi_init);
+                       return 0;
+               }
                else
                        return 0; /* no scaling needed */
        }
@@ -384,15 +497,67 @@ int scale_velocity(t_moldyn *moldyn,u8 equi_init) {
                scale*=2.0;
        else
                if(moldyn->pt_scale&T_SCALE_BERENDSEN)
-                       scale=1.0+moldyn->tau*(scale-1.0)/moldyn->t_tc;
+                       scale=1.0+(scale-1.0)/moldyn->t_tc;
        scale=sqrt(scale);
 
        /* velocity scaling */
-       for(i=0;i<moldyn->count;i++)
+       for(i=0;i<moldyn->count;i++) {
                if((equi_init&TRUE)||(atom[i].attr&ATOM_ATTR_HB))
                        v3_scale(&(atom[i].v),&(atom[i].v),scale);
+       }
+
+       return 0;
+}
+
+int scale_volume(t_moldyn *moldyn) {
+
+       t_atom *atom;
+       t_3dvec *dim,*vdim;
+       double virial,scale;
+       t_linkcell *lc;
+       int i;
+
+       atom=moldyn->atom;
+       dim=&(moldyn->dim);
+       vdim=&(moldyn->vis.dim);
+       lc=&(moldyn->lc);
+
+       for(i=0;i<moldyn->count;i++)
+               virial+=v3_norm(&(atom[i].virial));
+
+printf("%f\n",virial);
+       /* get pressure from virial */
+       moldyn->p=moldyn->count*K_BOLTZMANN*moldyn->t-ONE_THIRD*virial;
+       moldyn->p/=moldyn->volume;
+printf("%f\n",moldyn->p/(ATM));
+
+       /* scale factor */
+       if(moldyn->pt_scale&P_SCALE_BERENDSEN)
+               scale=3*sqrt(1-(moldyn->p_ref-moldyn->p)/moldyn->p_tc);
+       else 
+               /* should actually never be used */
+               scale=pow(moldyn->p/moldyn->p_ref,1.0/3.0);
+
+printf("scale = %f\n",scale);
+       /* actual scaling */
+       dim->x*=scale;
+       dim->y*=scale;
+       dim->z*=scale;
+       if(vdim->x) vdim->x=dim->x;
+       if(vdim->y) vdim->y=dim->y;
+       if(vdim->z) vdim->z=dim->z;
+       moldyn->volume*=(scale*scale*scale);
+
+       /* check whether we need a new linkcell init */
+       if((dim->x/moldyn->cutoff!=lc->nx)||
+          (dim->y/moldyn->cutoff!=lc->ny)||
+          (dim->z/moldyn->cutoff!=lc->nx)) {
+               link_cell_shutdown(moldyn);
+               link_cell_init(moldyn);
+       }
 
        return 0;
+
 }
 
 double get_e_kin(t_moldyn *moldyn) {
@@ -447,12 +612,6 @@ double estimate_time_step(t_moldyn *moldyn,double nn_dist) {
 
        /* nn_dist is the nearest neighbour distance */
 
-       if(moldyn->t==5.0) {
-               printf("[moldyn] i do not estimate timesteps below %f K!\n",
-                      MOLDYN_CRITICAL_EST_TEMP);
-               return 23.42;
-       }
-
        tau=(0.05*nn_dist*moldyn->atom[0].mass)/sqrt(3.0*K_BOLTZMANN*moldyn->t);
 
        return tau;     
@@ -468,9 +627,6 @@ int link_cell_init(t_moldyn *moldyn) {
 
        t_linkcell *lc;
        int i;
-       int fd;
-
-       fd=open("/dev/null",O_WRONLY);
 
        lc=&(moldyn->lc);
 
@@ -488,8 +644,7 @@ int link_cell_init(t_moldyn *moldyn) {
        printf("[moldyn] initializing linked cells (%d)\n",lc->cells);
 
        for(i=0;i<lc->cells;i++)
-               //list_init(&(lc->subcell[i]),1);
-               list_init(&(lc->subcell[i]),fd);
+               list_init_f(&(lc->subcell[i]));
 
        link_cell_update(moldyn);
        
@@ -499,26 +654,30 @@ int link_cell_init(t_moldyn *moldyn) {
 int link_cell_update(t_moldyn *moldyn) {
 
        int count,i,j,k;
-       int nx,ny,nz;
+       int nx,ny;
        t_atom *atom;
        t_linkcell *lc;
+       double x,y,z;
 
        atom=moldyn->atom;
        lc=&(moldyn->lc);
 
        nx=lc->nx;
        ny=lc->ny;
-       nz=lc->nz;
+
+       x=moldyn->dim.x/2;
+       y=moldyn->dim.y/2;
+       z=moldyn->dim.z/2;
 
        for(i=0;i<lc->cells;i++)
-               list_destroy(&(moldyn->lc.subcell[i]));
+               list_destroy_f(&(lc->subcell[i]));
        
        for(count=0;count<moldyn->count;count++) {
-               i=(atom[count].r.x+(moldyn->dim.x/2))/lc->x;
-               j=(atom[count].r.y+(moldyn->dim.y/2))/lc->y;
-               k=(atom[count].r.z+(moldyn->dim.z/2))/lc->z;
-               list_add_immediate_ptr(&(moldyn->lc.subcell[i+j*nx+k*nx*ny]),
-                                      &(atom[count]));
+               i=((atom[count].r.x+(moldyn->dim.x/2))/lc->x);
+               j=((atom[count].r.y+(moldyn->dim.y/2))/lc->y);
+               k=((atom[count].r.z+(moldyn->dim.z/2))/lc->z);
+               list_add_immediate_f(&(moldyn->lc.subcell[i+j*nx+k*nx*ny]),
+                                    &(atom[count]));
        }
 
        return 0;
@@ -588,7 +747,9 @@ int link_cell_shutdown(t_moldyn *moldyn) {
        lc=&(moldyn->lc);
 
        for(i=0;i<lc->nx*lc->ny*lc->nz;i++)
-               list_shutdown(&(moldyn->lc.subcell[i]));
+               list_destroy_f(&(moldyn->lc.subcell[i]));
+
+       free(lc->subcell);
 
        return 0;
 }
@@ -645,7 +806,7 @@ int moldyn_integrate(t_moldyn *moldyn) {
        t_moldyn_schedule *schedule;
        t_atom *atom;
        int fd;
-       char fb[128];
+       char dir[128];
        double ds;
 
        schedule=&(moldyn->schedule);
@@ -681,7 +842,7 @@ int moldyn_integrate(t_moldyn *moldyn) {
        /* zero absolute time */
        moldyn->time=0.0;
 
-       /* debugging, ignre */
+       /* debugging, ignore */
        moldyn->debug=0;
 
        /* executing the schedule */
@@ -697,21 +858,19 @@ int moldyn_integrate(t_moldyn *moldyn) {
        for(i=0;i<moldyn->time_steps;i++) {
 
                /* integration step */
-printf("MOVE\n");
                moldyn->integrate(moldyn);
 
                /* p/t scaling */
                if(moldyn->pt_scale&(T_SCALE_BERENDSEN|T_SCALE_DIRECT))
                        scale_velocity(moldyn,FALSE);
-
-               /* increase absolute time */
-               moldyn->time+=moldyn->tau;
+               if(moldyn->pt_scale&(P_SCALE_BERENDSEN|P_SCALE_DIRECT))
+                       scale_volume(moldyn);
 
                /* check for log & visualization */
                if(e) {
                        if(!(i%e))
                                dprintf(moldyn->efd,
-                                       "%.15f %.45f %.45f %.45f\n",
+                                       "%f %f %f %f\n",
                                        moldyn->time,update_e_kin(moldyn),
                                        moldyn->energy,
                                        get_total_energy(moldyn));
@@ -720,15 +879,14 @@ printf("MOVE\n");
                        if(!(i%m)) {
                                p=get_total_p(moldyn);
                                dprintf(moldyn->mfd,
-                                       "%.15f %.45f\n",moldyn->time,
-                                       v3_norm(&p));
+                                       "%f %f\n",moldyn->time,v3_norm(&p));
                        }
                }
                if(s) {
                        if(!(i%s)) {
-                               snprintf(fb,128,"%s-%f-%.15f.save",moldyn->sfb,
-                                        moldyn->t,i*moldyn->tau);
-                               fd=open(fb,O_WRONLY|O_TRUNC|O_CREAT);
+                               snprintf(dir,128,"%s/s-%07.f.save",
+                                        moldyn->vlsdir,moldyn->time);
+                               fd=open(dir,O_WRONLY|O_TRUNC|O_CREAT);
                                if(fd<0) perror("[moldyn] save fd open");
                                else {
                                        write(fd,moldyn,sizeof(t_moldyn));
@@ -742,12 +900,15 @@ printf("MOVE\n");
                        if(!(i%v)) {
                                visual_atoms(&(moldyn->vis),moldyn->time,
                                             moldyn->atom,moldyn->count);
-                               printf("\rsched: %d, steps: %d, theta: %d",
+                               printf("\rsched: %d, steps: %d, debug: %d",
                                       sched,i,moldyn->debug);
                                fflush(stdout);
                        }
                }
 
+               /* increase absolute time */
+               moldyn->time+=moldyn->tau;
+
        }
 
                /* check for hooks */
@@ -820,7 +981,6 @@ int potential_force_calc(t_moldyn *moldyn) {
        t_linkcell *lc;
        t_list neighbour_i[27];
        t_list neighbour_i2[27];
-       //t_list neighbour_j[27];
        t_list *this,*that;
        u8 bc_ij,bc_ik;
        int dnlc;
@@ -831,104 +991,113 @@ int potential_force_calc(t_moldyn *moldyn) {
 
        /* reset energy */
        moldyn->energy=0.0;
-
+       
        /* get energy and force of every atom */
        for(i=0;i<count;i++) {
 
                /* reset force */
                v3_zero(&(itom[i].f));
 
+               /* reset viral of atom i */
+               v3_zero(&(itom[i].virial));
+
                /* single particle potential/force */
                if(itom[i].attr&ATOM_ATTR_1BP)
                        moldyn->func1b(moldyn,&(itom[i]));
 
+               if(!(itom[i].attr&(ATOM_ATTR_2BP|ATOM_ATTR_3BP)))
+                       continue;
+
                /* 2 body pair potential/force */
-               if(itom[i].attr&(ATOM_ATTR_2BP|ATOM_ATTR_3BP)) {
        
-                       link_cell_neighbour_index(moldyn,
-                               (itom[i].r.x+moldyn->dim.x/2)/lc->x,
-                               (itom[i].r.y+moldyn->dim.y/2)/lc->y,
-                               (itom[i].r.z+moldyn->dim.z/2)/lc->z,
-                               neighbour_i);
+               link_cell_neighbour_index(moldyn,
+                                         (itom[i].r.x+moldyn->dim.x/2)/lc->x,
+                                         (itom[i].r.y+moldyn->dim.y/2)/lc->y,
+                                         (itom[i].r.z+moldyn->dim.z/2)/lc->z,
+                                         neighbour_i);
 
-                       dnlc=lc->dnlc;
+               dnlc=lc->dnlc;
 
-                       for(j=0;j<27;j++) {
+               for(j=0;j<27;j++) {
 
-                               this=&(neighbour_i[j]);
-                               list_reset(this);
+                       this=&(neighbour_i[j]);
+                       list_reset_f(this);
 
-                               if(this->start==NULL)
-                                       continue;
+                       if(this->start==NULL)
+                               continue;
 
-                               bc_ij=(j<dnlc)?0:1;
+                       bc_ij=(j<dnlc)?0:1;
 
-                               do {
-                                       jtom=this->current->data;
+                       do {
+                               jtom=this->current->data;
 
-                                       if(jtom==&(itom[i]))
-                                               continue;
+                               if(jtom==&(itom[i]))
+                                       continue;
 
-                                       if((jtom->attr&ATOM_ATTR_2BP)&
-                                          (itom[i].attr&ATOM_ATTR_2BP))
-                                               moldyn->func2b(moldyn,
-                                                              &(itom[i]),
-                                                              jtom,
-                                                              bc_ij);
+                               if((jtom->attr&ATOM_ATTR_2BP)&
+                                  (itom[i].attr&ATOM_ATTR_2BP)) {
+                                       moldyn->func2b(moldyn,
+                                                      &(itom[i]),
+                                                      jtom,
+                                                      bc_ij);
+                               }
 
-                                       /* 3 body potential/force */
+                               /* 3 body potential/force */
 
-                                       if(!(itom[i].attr&ATOM_ATTR_3BP)||
-                                          !(jtom->attr&ATOM_ATTR_3BP))
-                                               continue;
+                               if(!(itom[i].attr&ATOM_ATTR_3BP)||
+                                  !(jtom->attr&ATOM_ATTR_3BP))
+                                       continue;
 
-                                       /* copy the neighbour lists */
-                                       memcpy(neighbour_i2,neighbour_i,
-                                              27*sizeof(t_list));
+                               /* copy the neighbour lists */
+                               memcpy(neighbour_i2,neighbour_i,
+                                      27*sizeof(t_list));
 
-                                       /* get neighbours of i */
-                                       for(k=0;k<27;k++) {
+                               /* get neighbours of i */
+                               for(k=0;k<27;k++) {
 
-                                               that=&(neighbour_i2[k]);
-                                               list_reset(that);
+                                       that=&(neighbour_i2[k]);
+                                       list_reset_f(that);
                                        
-                                               if(that->start==NULL)
-                                                       continue;
+                                       if(that->start==NULL)
+                                               continue;
 
-                                               bc_ik=(k<dnlc)?0:1;
+                                       bc_ik=(k<dnlc)?0:1;
 
-                                               do {
+                                       do {
 
-                       ktom=that->current->data;
+                                               ktom=that->current->data;
 
-                       if(!(ktom->attr&ATOM_ATTR_3BP))
-                               continue;
+                                               if(!(ktom->attr&ATOM_ATTR_3BP))
+                                                       continue;
 
-                       if(ktom==jtom)
-                               continue;
+                                               if(ktom==jtom)
+                                                       continue;
 
-                       if(ktom==&(itom[i]))
-                               continue;
+                                               if(ktom==&(itom[i]))
+                                                       continue;
 
-                       moldyn->func3b(moldyn,&(itom[i]),jtom,ktom,bc_ik|bc_ij);
+                                               moldyn->func3b(moldyn,
+                                                              &(itom[i]),
+                                                              jtom,
+                                                              ktom,
+                                                              bc_ik|bc_ij);
 
-                                               } while(list_next(that)!=\
-                                                       L_NO_NEXT_ELEMENT);
+                                       } while(list_next_f(that)!=\
+                                               L_NO_NEXT_ELEMENT);
+
+                               }
 
-                                       }
-                                       
-                               } while(list_next(this)!=L_NO_NEXT_ELEMENT);
-               
                                /* 2bp post function */
                                if(moldyn->func2b_post) {
                                        moldyn->func2b_post(moldyn,
                                                            &(itom[i]),
                                                            jtom,bc_ij);
                                }
-
-                       }
+                                       
+                       } while(list_next_f(this)!=L_NO_NEXT_ELEMENT);
+               
                }
-printf("debug atom %d: %.15f %.15f %.15f\n",i,itom[i].r.x,itom[i].v.x,itom[i].f.x);
+
        }
 
        return 0;
@@ -938,16 +1107,16 @@ printf("debug atom %d: %.15f %.15f %.15f\n",i,itom[i].r.x,itom[i].v.x,itom[i].f.
  * periodic boundayr checking
  */
 
-int check_per_bound(t_moldyn *moldyn,t_3dvec *a) {
+inline int check_per_bound(t_moldyn *moldyn,t_3dvec *a) {
        
        double x,y,z;
        t_3dvec *dim;
 
        dim=&(moldyn->dim);
 
-       x=0.5*dim->x;
-       y=0.5*dim->y;
-       z=0.5*dim->z;
+       x=dim->x/2;
+       y=dim->y/2;
+       z=dim->z/2;
 
        if(moldyn->status&MOLDYN_STAT_PBX) {
                if(a->x>=x) a->x-=dim->x;
@@ -983,14 +1152,15 @@ int harmonic_oscillator(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
        sc=params->spring_constant;
        equi_dist=params->equilibrium_distance;
 
-       v3_sub(&distance,&(ai->r),&(aj->r));
+       v3_sub(&distance,&(aj->r),&(ai->r));
        
        if(bc) check_per_bound(moldyn,&distance);
        d=v3_norm(&distance);
        if(d<=moldyn->cutoff) {
                /* energy is 1/2 (d-d0)^2, but we will add this twice ... */
                moldyn->energy+=(0.25*sc*(d-equi_dist)*(d-equi_dist));
-               v3_scale(&force,&distance,-sc*(1.0-(equi_dist/d)));
+               /* f = -grad E; grad r_ij = -1 1/r_ij distance */
+               v3_scale(&force,&distance,sc*(1.0-(equi_dist/d)));
                v3_add(&(ai->f),&(ai->f),&force);
        }
 
@@ -1011,7 +1181,7 @@ int lennard_jones(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
        sig6=params->sigma6;
        sig12=params->sigma12;
 
-       v3_sub(&distance,&(ai->r),&(aj->r));
+       v3_sub(&distance,&(aj->r),&(ai->r));
        if(bc) check_per_bound(moldyn,&distance);
        d=v3_absolute_square(&distance);        /* 1/r^2 */
        if(d<=moldyn->cutoff_square) {
@@ -1027,7 +1197,7 @@ int lennard_jones(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
                h1*=12*sig12;
                d=+h1-h2;
                d*=eps;
-               v3_scale(&force,&distance,d);
+               v3_scale(&force,&distance,-1.0*d); /* f = - grad E */
                v3_add(&(ai->f),&(ai->f),&force);
        }
 
@@ -1050,8 +1220,8 @@ int tersoff_mult_complete_params(t_tersoff_mult_params *p) {
        p->mu_m=0.5*(p->mu[0]+p->mu[1]);
 
        printf("[moldyn] tersoff mult parameter info:\n");
-       printf("  S (m)  | %.12f | %.12f | %.12f\n",p->S[0],p->S[1],p->Smixed);
-       printf("  R (m)  | %.12f | %.12f | %.12f\n",p->R[0],p->R[1],p->Rmixed);
+       printf("  S (A)  | %f | %f | %f\n",p->S[0],p->S[1],p->Smixed);
+       printf("  R (A)  | %f | %f | %f\n",p->R[0],p->R[1],p->Rmixed);
        printf("  A (eV) | %f | %f | %f\n",p->A[0]/EV,p->A[1]/EV,p->Amixed/EV);
        printf("  B (eV) | %f | %f | %f\n",p->B[0]/EV,p->B[1]/EV,p->Bmixed/EV);
        printf("  lambda | %f | %f | %f\n",p->lambda[0],p->lambda[1],
@@ -1083,17 +1253,16 @@ int tersoff_mult_1bp(t_moldyn *moldyn,t_atom *ai) {
         *         their right values
         */
 
-       exchange->beta=&(params->beta[num]);
-       exchange->n=&(params->n[num]);
-       exchange->c=&(params->c[num]);
-       exchange->d=&(params->d[num]);
-       exchange->h=&(params->h[num]);
+       exchange->beta_i=&(params->beta[num]);
+       exchange->n_i=&(params->n[num]);
+       exchange->c_i=&(params->c[num]);
+       exchange->d_i=&(params->d[num]);
+       exchange->h_i=&(params->h[num]);
 
-       exchange->betan=pow(*(exchange->beta),*(exchange->n));
-       exchange->n_betan=*(exchange->n)*exchange->betan;
-       exchange->c2=params->c[num]*params->c[num];
-       exchange->d2=params->d[num]*params->d[num];
-       exchange->c2d2=exchange->c2/exchange->d2;
+       exchange->betaini=pow(*(exchange->beta_i),*(exchange->n_i));
+       exchange->ci2=params->c[num]*params->c[num];
+       exchange->di2=params->d[num]*params->d[num];
+       exchange->ci2di2=exchange->ci2/exchange->di2;
 
        return 0;
 }
@@ -1111,25 +1280,34 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
        int num;
        double s_r;
        double arg;
-       double scale;
 
        params=moldyn->pot2b_params;
-       num=ai->bnum;
+       num=aj->bnum;
        exchange=&(params->exchange);
 
+       /* clear 3bp and 2bp post run */
        exchange->run3bp=0;
        exchange->run2bp_post=0;
+
+       /* reset S > r > R mark */
+       exchange->d_ij_between_rs=0;
        
        /*
-        * we need: f_c, df_c, f_r, df_r
+        * calc of 2bp contribution of V_ij and dV_ij/ji
+        *
+        * for Vij and dV_ij we need:
+        * - f_c_ij, df_c_ij
+        * - f_r_ij, df_r_ij
+        *
+        * for dV_ji we need:
+        * - f_c_ji = f_c_ij, df_c_ji = df_c_ij
+        * - f_r_ji = f_r_ij; df_r_ji = df_r_ij
         *
-        * therefore we need: R, S, A, lambda
         */
 
-       v3_sub(&dist_ij,&(ai->r),&(aj->r));
-
+       /* dist_ij, d_ij */
+       v3_sub(&dist_ij,&(aj->r),&(ai->r));
        if(bc) check_per_bound(moldyn,&dist_ij);
-
        d_ij=v3_norm(&dist_ij);
 
        /* save for use in 3bp */
@@ -1137,14 +1315,14 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
        exchange->dist_ij=dist_ij;
 
        /* constants */
-       if(num==aj->bnum) {
+       if(num==ai->bnum) {
                S=params->S[num];
                R=params->R[num];
                A=params->A[num];
                B=params->B[num];
                lambda=params->lambda[num];
                mu=params->mu[num];
-               params->exchange.chi=1.0;
+               exchange->chi=1.0;
        }
        else {
                S=params->Smixed;
@@ -1155,34 +1333,63 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
                mu=params->mu_m;
                params->exchange.chi=params->chi;
        }
+
+       /* if d_ij > S => no force & potential energy contribution */
        if(d_ij>S)
                return 0;
 
+       /* more constants */
+       exchange->beta_j=&(params->beta[num]);
+       exchange->n_j=&(params->n[num]);
+       exchange->c_j=&(params->c[num]);
+       exchange->d_j=&(params->d[num]);
+       exchange->h_j=&(params->h[num]);
+       if(num==ai->bnum) {
+               exchange->betajnj=exchange->betaini;
+               exchange->cj2=exchange->ci2;
+               exchange->dj2=exchange->di2;
+               exchange->cj2dj2=exchange->ci2di2;
+       }
+       else {
+               exchange->betajnj=pow(*(exchange->beta_j),*(exchange->n_j));
+               exchange->cj2=params->c[num]*params->c[num];
+               exchange->dj2=params->d[num]*params->d[num];
+               exchange->cj2dj2=exchange->cj2/exchange->dj2;
+       }
+
+       /* f_r_ij = f_r_ji, df_r_ij = df_r_ji */
        f_r=A*exp(-lambda*d_ij);
-       df_r=-lambda*f_r/d_ij;
+       df_r=lambda*f_r/d_ij;
 
-       /* f_a, df_a calc + save for later use */
+       /* f_a, df_a calc (again, same for ij and ji) | save for later use! */
        exchange->f_a=-B*exp(-mu*d_ij);
-       exchange->df_a=-mu*exchange->f_a/d_ij;
+       exchange->df_a=mu*exchange->f_a/d_ij;
 
+       /* f_c, df_c calc (again, same for ij and ji) */
        if(d_ij<R) {
                /* f_c = 1, df_c = 0 */
                f_c=1.0;
                df_c=0.0;
-               v3_scale(&force,&dist_ij,df_r);
+               /* two body contribution (ij, ji) */
+               v3_scale(&force,&dist_ij,-df_r);
        }
        else {
                s_r=S-R;
                arg=M_PI*(d_ij-R)/s_r;
                f_c=0.5+0.5*cos(arg);
-               df_c=-0.5*sin(arg)*(M_PI/(s_r*d_ij));
-               scale=df_c*f_r+df_r*f_c;
-               v3_scale(&force,&dist_ij,scale);
+               //df_c=-0.5*sin(arg)*(M_PI/(s_r*d_ij)); /* MARK! */
+               df_c=0.5*sin(arg)*(M_PI/(s_r*d_ij));
+               /* two body contribution (ij, ji) */
+               v3_scale(&force,&dist_ij,-df_c*f_r-df_r*f_c);
+               /* tell 3bp that S > r > R */
+               exchange->d_ij_between_rs=1;
        }
 
-       /* add forces */
+       /* add forces of 2bp (ij, ji) contribution
+        * dVij = dVji and we sum up both: no 1/2) */
        v3_add(&(ai->f),&(ai->f),&force);
-       /* energy is 0.5 f_r f_c ... */
+
+       /* energy 2bp contribution (ij, ji) is 0.5 f_r f_c ... */
        moldyn->energy+=(0.5*f_r*f_c);
 
        /* save for use in 3bp */
@@ -1194,8 +1401,10 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
        exchange->run2bp_post=1;
 
        /* reset 3bp sums */
-       exchange->zeta=0.0;
-       v3_zero(&(exchange->db_ij));
+       exchange->zeta_ij=0.0;
+       exchange->zeta_ji=0.0;
+       v3_zero(&(exchange->dzeta_ij));
+       v3_zero(&(exchange->dzeta_ji));
 
        return 0;
 }
@@ -1204,16 +1413,27 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 
 int tersoff_mult_post_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 
-       /* here we have to allow for the 3bp sums */
+       /*
+        * here we have to allow for the 3bp sums
+        *
+        * that is:
+        * - zeta_ij, dzeta_ij
+        * - zeta_ji, dzeta_ji
+        *
+        * to compute the 3bp contribution to:
+        * - Vij, dVij
+        * - dVji
+        *
+        */
 
        t_tersoff_mult_params *params;
        t_tersoff_exchange *exchange;
 
-       t_3dvec force,temp,*db_ij,*dist_ij;
-       double db_ij_scale1,db_ij_scale2;
-       double b_ij;
+       t_3dvec force,temp;
+       t_3dvec *dist_ij;
+       double b,db,tmp;
        double f_c,df_c,f_a,df_a;
-       double chi,n,n_betan;
+       double chi,ni,betaini,nj,betajnj;
        double zeta;
 
        params=moldyn->pot2b_params;
@@ -1223,44 +1443,70 @@ int tersoff_mult_post_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
        if(!(exchange->run2bp_post))
                return 0;
 
-       db_ij=&(exchange->db_ij);
        f_c=exchange->f_c;
        df_c=exchange->df_c;
        f_a=exchange->f_a;
        df_a=exchange->df_a;
-       n_betan=exchange->n_betan;
-       n=*(exchange->n);
+       betaini=exchange->betaini;
+       betajnj=exchange->betajnj;
+       ni=*(exchange->n_i);
+       nj=*(exchange->n_j);
        chi=exchange->chi;
        dist_ij=&(exchange->dist_ij);
-       zeta=exchange->zeta;
-
-       db_ij_scale2=pow(zeta,n-1.0);
-printf("DEBUG: %.15f %.15f\n",zeta,db_ij_scale2);
-       db_ij_scale1=db_ij_scale2*zeta;
-       db_ij_scale2*=n_betan;
-       db_ij_scale1=pow((1.0+n_betan*db_ij_scale1),-1.0/(2*n)-1);
-       b_ij=chi*db_ij_scale1*(1.0+n_betan*db_ij_scale1);
-       db_ij_scale1*=(-1.0*chi/(2*n));
-
-       /* db_ij part */
-       v3_scale(db_ij,db_ij,(db_ij_scale1*db_ij_scale2));
-       v3_scale(db_ij,db_ij,f_a);
-
-       /* df_a part */
-       v3_scale(&temp,dist_ij,b_ij*df_a);
-
-       /* db_ij + df_a part */
-       v3_add(&force,&temp,db_ij);
-       v3_scale(&force,&force,f_c);
+       
+       /* Vij and dVij */
+       zeta=exchange->zeta_ij;
+       if(zeta==0.0) {
+               moldyn->debug++;                /* just for debugging ... */
+               db=0.0;
+               b=chi;
+               v3_scale(&force,dist_ij,df_a*b*f_c);
+       }
+       else {
+               tmp=betaini*pow(zeta,ni-1.0);           /* beta^n * zeta^n-1 */
+               b=(1+zeta*tmp);                         /* 1 + beta^n zeta^n */
+               db=chi*pow(b,-1.0/(2*ni)-1);            /* x(...)^(-1/2n - 1) */
+               b=db*b;                                 /* b_ij */
+               db*=-0.5*tmp;                           /* db_ij */
+               v3_scale(&force,&(exchange->dzeta_ij),f_a*db);
+               v3_scale(&temp,dist_ij,df_a*b);
+               v3_add(&force,&force,&temp);
+               v3_scale(&force,&force,f_c);
+       }
+       v3_scale(&temp,dist_ij,df_c*b*f_a);
+       v3_add(&force,&force,&temp);
+       v3_scale(&force,&force,-0.5);
 
-       /* df_c part */
-       v3_scale(&temp,dist_ij,f_a*b_ij*df_c);
+       /* add force */
+       v3_add(&(ai->f),&(ai->f),&force);
 
        /* add energy of 3bp sum */
-       moldyn->energy+=(0.5*f_c*b_ij*f_a);
+       moldyn->energy+=(0.5*f_c*b*f_a);
+
+       /* dVji */
+       zeta=exchange->zeta_ji;
+       if(zeta==0.0) {
+               moldyn->debug++;
+               b=chi;
+               v3_scale(&force,dist_ij,df_a*b*f_c);
+       }
+       else {
+               tmp=betajnj*pow(zeta,nj-1.0);           /* beta^n * zeta^n-1 */
+               b=(1+zeta*tmp);                         /* 1 + beta^n zeta^n */
+               db=chi*pow(b,-1.0/(2*nj)-1);            /* x(...)^(-1/2n - 1) */
+               b=db*b;                                 /* b_ij */
+               db*=-0.5*tmp;                           /* db_ij */
+               v3_scale(&force,&(exchange->dzeta_ji),f_a*db);
+               v3_scale(&temp,dist_ij,df_a*b);
+               v3_add(&force,&force,&temp);
+               v3_scale(&force,&force,f_c);
+       }
+       v3_scale(&temp,dist_ij,df_c*b*f_a);
+       v3_add(&force,&force,&temp);
+       v3_scale(&force,&force,-0.5);
 
-       /* add force of 3bp calculation (all three parts) */
-       v3_add(&(ai->f),&temp,&force);
+       /* add force */
+       v3_add(&(ai->f),&(ai->f),&force);
 
        return 0;
 }
@@ -1271,59 +1517,75 @@ int tersoff_mult_3bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,t_atom *ak,u8 bc) {
 
        t_tersoff_mult_params *params;
        t_tersoff_exchange *exchange;
-       t_3dvec dist_ij,dist_ik;
-       t_3dvec temp,force;
+       t_3dvec dist_ij,dist_ik,dist_jk;
+       t_3dvec temp1,temp2;
+       t_3dvec *dzeta;
        double R,S,s_r;
-       double d_ij,d_ik;
-       double rijrik,dijdik;
-       double f_c,df_c,f_a,df_a;
+       double B,mu;
+       double d_ij,d_ik,d_jk;
+       double rr,dd;
+       double f_c,df_c;
        double f_c_ik,df_c_ik,arg;
+       double f_c_jk;
        double n,c,d,h;
        double c2,d2,c2d2;
        double cos_theta,d_costheta1,d_costheta2;
        double h_cos,d2_h_cos2;
-       double frac;
-       double g;
+       double frac,g,zeta,chi;
+       double tmp;
        int num;
 
        params=moldyn->pot3b_params;
-       num=ai->bnum;
        exchange=&(params->exchange);
 
        if(!(exchange->run3bp))
                return 0;
 
        /*
-        * we need: f_c, d_fc, b_ij, db_ij, f_a, df_a
+        * calc of 3bp contribution of V_ij and dV_ij/ji/jk &
+        * 2bp contribution of dV_jk
+        *
+        * for Vij and dV_ij we still need:
+        * - b_ij, db_ij (zeta_ij)
+        *   - f_c_ik, df_c_ik, constants_i, cos_theta_ijk, d_costheta_ijk
+        *
+        * for dV_ji we still need:
+        * - b_ji, db_ji (zeta_ji)
+        *   - f_c_jk, d_c_jk, constants_j, cos_theta_jik, d_costheta_jik
+        *
+        * for dV_jk we need:
+        * - f_c_jk
+        * - f_a_jk
+        * - db_jk (zeta_jk)
+        *   - f_c_ji, df_c_ji, constants_j, cos_theta_jki, d_costheta_jki
         *
-        * we got f_c, df_c, f_a, df_a from 2bp calculation
         */
 
-       d_ij=exchange->d_ij;
-       dist_ij=exchange->dist_ij;
+       /*
+        * get exchange data 
+        */
 
-       f_a=params->exchange.f_a;
-       df_a=params->exchange.df_a;
+       /* dist_ij, d_ij - this is < S_ij ! */
+       dist_ij=exchange->dist_ij;
+       d_ij=exchange->d_ij;
 
+       /* f_c_ij, df_c_ij (same for ji) */
        f_c=exchange->f_c;
        df_c=exchange->df_c;
-       
-       /* d_ij is <= S, as we didn't return so far! */
 
        /*
-        * calc of b_ij (scalar) and db_ij (vector)
-        *
-        * - for b_ij: chi, beta, f_c_ik, w(=1), c, d, h, n, cos_theta
-        *
-        * - for db_ij: d_costheta, cos_theta, f_c_ik, df_c_ik, w_ik
-        *
+        * calculate unknown values now ...
         */
 
-       v3_sub(&dist_ik,&(ai->r),&(ak->r));
+       /* V_ij and dV_ij stuff (in b_ij there is f_c_ik) */
+
+       /* dist_ik, d_ik */
+       v3_sub(&dist_ik,&(ak->r),&(ai->r));
        if(bc) check_per_bound(moldyn,&dist_ik);
        d_ik=v3_norm(&dist_ik);
 
-       /* constants */
+       /* ik constants */
+       num=ai->bnum;
        if(num==ak->bnum) {
                R=params->R[num];
                S=params->S[num];
@@ -1333,84 +1595,234 @@ int tersoff_mult_3bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,t_atom *ak,u8 bc) {
                S=params->Smixed;
        }
 
-       /* there is no contribution if f_c_ik = 0 */
-       if(d_ik>S)
-               return 0;
-
-       /* get exchange data */
-       n=*(exchange->n);
-       c=*(exchange->c);
-       d=*(exchange->d);
-       h=*(exchange->h);
-       c2=exchange->c2;
-       d2=exchange->d2;
-       c2d2=exchange->c2d2;
-
-       /* cosine of theta by scalaproduct */
-       rijrik=v3_scalar_product(&dist_ij,&dist_ik);
-       dijdik=d_ij*d_ik;
-       cos_theta=rijrik/dijdik;
-
-       /* hack - cos theta machine accuracy problems! */
-       if(cos_theta>1.0||cos_theta<-1.0) {
-               printf("THETA CORRECTION\n");
-               moldyn->debug++;
-               if(fabs(cos_theta)>1.0+ACCEPTABLE_ERROR)
-                       printf("[moldyn] WARNING: cos theta failure!\n");
-               if(cos_theta<0) {
-                       cos_theta=-1.0;
+       /* zeta_ij/dzeta_ij contribution only for d_ik < S */
+       if(d_ik<S) {
+
+               /* get constants_i from exchange data */
+               n=*(exchange->n_i);
+               c=*(exchange->c_i);
+               d=*(exchange->d_i);
+               h=*(exchange->h_i);
+               c2=exchange->ci2;
+               d2=exchange->di2;
+               c2d2=exchange->ci2di2;
+
+               /* cosine of theta_ijk by scalaproduct */
+               rr=v3_scalar_product(&dist_ij,&dist_ik);
+               dd=d_ij*d_ik;
+               cos_theta=rr/dd;
+
+               /* d_costheta */
+               tmp=1.0/dd;
+               d_costheta1=cos_theta/(d_ij*d_ij)-tmp;
+               d_costheta2=cos_theta/(d_ik*d_ik)-tmp;
+
+               /* some usefull values */
+               h_cos=(h-cos_theta);
+               d2_h_cos2=d2+(h_cos*h_cos);
+               frac=c2/(d2_h_cos2);
+
+               /* g(cos_theta) */
+               g=1.0+c2d2-frac;
+
+               /* d_costheta_ij and dg(cos_theta) - needed in any case! */
+               v3_scale(&temp1,&dist_ij,d_costheta1);
+               v3_scale(&temp2,&dist_ik,d_costheta2);
+               v3_add(&temp1,&temp1,&temp2);
+               v3_scale(&temp1,&temp1,-2.0*frac*h_cos/d2_h_cos2); /* dg */
+
+               /* f_c_ik & df_c_ik + {d,}zeta contribution */
+               dzeta=&(exchange->dzeta_ij);
+               if(d_ik<R) {
+                       /* {d,}f_c_ik */
+                       // => f_c_ik=1.0;
+                       // => df_c_ik=0.0; of course we do not set this!
+
+                       /* zeta_ij */
+                       exchange->zeta_ij+=g;
+
+                       /* dzeta_ij */
+                       v3_add(dzeta,dzeta,&temp1);
                }
                else {
-                       cos_theta=1.0;
+                       /* {d,}f_c_ik */
+                       s_r=S-R;
+                       arg=M_PI*(d_ik-R)/s_r;
+                       f_c_ik=0.5+0.5*cos(arg);
+                       //df_c_ik=-0.5*sin(arg)*(M_PI/(s_r*d_ik)); /* MARK */
+                       df_c_ik=0.5*sin(arg)*(M_PI/(s_r*d_ik));
+
+                       /* zeta_ij */
+                       exchange->zeta_ij+=f_c_ik*g;
+
+                       /* dzeta_ij */
+                       v3_scale(&temp1,&temp1,f_c_ik);
+                       v3_scale(&temp2,&dist_ik,g*df_c_ik);
+                       v3_add(&temp1,&temp1,&temp2);
+                       v3_add(dzeta,dzeta,&temp1);
                }
        }
 
-       d_costheta1=dijdik-rijrik*d_ik/d_ij;
-       d_costheta2=dijdik-rijrik*d_ij/d_ik;
+       /* dV_ji stuff (in b_ji there is f_c_jk) + dV_jk stuff! */
+
+       /* dist_jk, d_jk */
+       v3_sub(&dist_jk,&(ak->r),&(aj->r));
+       if(bc) check_per_bound(moldyn,&dist_jk);
+       d_jk=v3_norm(&dist_jk);
+
+       /* jk constants */
+       num=aj->bnum;
+       if(num==ak->bnum) {
+               R=params->R[num];
+               S=params->S[num];
+               B=params->B[num];
+               mu=params->mu[num];
+               chi=1.0;
+       }
+       else {
+               R=params->Rmixed;
+               S=params->Smixed;
+               B=params->Bmixed;
+               mu=params->mu_m;
+               chi=params->chi;
+       }
 
-       h_cos=(h-cos_theta);
-       d2_h_cos2=d2+(h_cos*h_cos);
+       /* zeta_ji/dzeta_ji contribution only for d_jk < S_jk */
+       if(d_jk<S) {
+
+               /* constants_j from exchange data */
+               n=*(exchange->n_j);
+               c=*(exchange->c_j);
+               d=*(exchange->d_j);
+               h=*(exchange->h_j);
+               c2=exchange->cj2;
+               d2=exchange->dj2;
+               c2d2=exchange->cj2dj2;
+
+               /* cosine of theta_jik by scalaproduct */
+               rr=-v3_scalar_product(&dist_ij,&dist_jk); /* -1, as ij -> ji */
+               dd=d_ij*d_jk;
+               cos_theta=rr/dd;
+
+               /* d_costheta */
+               d_costheta1=1.0/dd;
+               d_costheta2=cos_theta/(d_ij*d_ij);
+
+               /* some usefull values */
+               h_cos=(h-cos_theta);
+               d2_h_cos2=d2+(h_cos*h_cos);
+               frac=c2/(d2_h_cos2);
+
+               /* g(cos_theta) */
+               g=1.0+c2d2-frac;
+
+               /* d_costheta_ij and dg(cos_theta) - needed in any case! */
+               v3_scale(&temp1,&dist_jk,d_costheta1);
+               v3_scale(&temp2,&dist_ij,-d_costheta2); /* ji -> ij => -1 */
+               v3_add(&temp1,&temp1,&temp2);
+               v3_scale(&temp1,&temp1,-2.0*frac*h_cos/d2_h_cos2); /* dg */
+
+               /* store dg in temp2 and use it for dVjk later */
+               v3_copy(&temp2,&temp1);
+
+               /* f_c_jk + {d,}zeta contribution (df_c_jk = 0) */
+               dzeta=&(exchange->dzeta_ji);
+               if(d_jk<R) {
+                       /* f_c_jk */
+                       f_c_jk=1.0;
+
+                       /* zeta_ji */
+                       exchange->zeta_ji+=g;
+
+                       /* dzeta_ji */
+                       v3_add(dzeta,dzeta,&temp1);
+               }
+               else {
+                       /* f_c_jk */
+                       s_r=S-R;
+                       arg=M_PI*(d_jk-R)/s_r;
+                       f_c_jk=0.5+0.5*cos(arg);
 
-       frac=c2/(d2_h_cos2);
-       g=1.0+c2d2-frac;
+                       /* zeta_ji */
+                       exchange->zeta_ji+=f_c_jk*g;
 
-       /* d_costheta contrib to db_ij (needed in all remaining cases) */
-       v3_scale(&temp,&dist_ij,d_costheta1);
-       v3_scale(&force,&dist_ik,d_costheta2);
-       v3_add(&force,&force,&temp);
-       v3_scale(&force,&force,-2.0*frac*h_cos/d2_h_cos2); /* f_c_ik missing */
+                       /* dzeta_ji */
+                       v3_scale(&temp1,&temp1,f_c_jk);
+                       v3_add(dzeta,dzeta,&temp1);
+               }
 
-       if(d_ik<R) {
-               /* f_c_ik = 1, df_c_ik = 0 */   
-               /* => only d_costheta contrib to db_ij */
-               // => do nothing ...
+               /* dV_jk stuff | add force contribution on atom i immediately */
+               if(exchange->d_ij_between_rs) {
+                       zeta=f_c*g;
+                       v3_scale(&temp1,&temp2,f_c);
+                       v3_scale(&temp2,&dist_ij,df_c*g);
+                       v3_add(&temp2,&temp2,&temp1); /* -> dzeta_jk in temp2 */
+               }
+               else {
+                       zeta=g;
+                       // dzeta_jk is simply dg, which is stored in temp2
+               }
+               /* betajnj * zeta_jk ^ nj-1 */
+               tmp=exchange->betajnj*pow(zeta,(n-1.0));
+               tmp=-chi/2.0*pow((1+tmp*zeta),(-1.0/(2.0*n)-1))*tmp;
+               v3_scale(&temp2,&temp2,tmp*B*exp(-mu*d_jk)*f_c_jk*0.5);
+               v3_add(&(ai->f),&(ai->f),&temp2); /* -1 skipped in f_a calc ^ */
+                                                 /* scaled with 0.5 ^ */
 
-               /* zeta, f_c_ik = 1 */
-               exchange->zeta+=g;
        }
-       else {
-               s_r=S-R;
-               arg=M_PI*(d_ik-R)/s_r;
-               f_c_ik=0.5+0.5*cos(arg);
-               df_c_ik=-0.5*sin(arg)*(M_PI/(s_r*d_ik));
 
-               /* scale d_costheta contrib with f_c_ik */
-               v3_scale(&force,&force,f_c_ik);
+       return 0;
+}
+
 
-               /* df_c_ik contrib to db_ij */
-               v3_scale(&temp,&dist_ik,df_c_ik*g);
+/*
+ * debugging / critical check functions
+ */
 
-               /* sum up both parts */
-               v3_add(&force,&force,&temp);
-               
-               /* zeta */
-               exchange->zeta+=f_c_ik*g;
+int moldyn_bc_check(t_moldyn *moldyn) {
+
+       t_atom *atom;
+       t_3dvec *dim;
+       int i;
+double x;
+u8 byte;
+int j,k;
+
+       atom=moldyn->atom;
+       dim=&(moldyn->dim);
+x=dim->x/2;
+
+       for(i=0;i<moldyn->count;i++) {
+               if(atom[i].r.x>=dim->x/2||-atom[i].r.x>dim->x/2) {
+                       printf("FATAL: atom %d: x: %.20f (%.20f)\n",
+                              i,atom[i].r.x,dim->x/2);
+                       printf("diagnostic:\n");
+                       printf("-----------\natom.r.x:\n");
+                       for(j=0;j<8;j++) {
+                               memcpy(&byte,(u8 *)(&(atom[i].r.x))+j,1);
+                               for(k=0;k<8;k++)
+                                       printf("%d%c",
+                                       ((byte)&(1<<k))?1:0,
+                                       (k==7)?'\n':'|');
+                       }
+                       printf("---------------\nx=dim.x/2:\n");
+                       for(j=0;j<8;j++) {
+                               memcpy(&byte,(u8 *)(&x)+j,1);
+                               for(k=0;k<8;k++)
+                                       printf("%d%c",
+                                       ((byte)&(1<<k))?1:0,
+                                       (k==7)?'\n':'|');
+                       }
+                       if(atom[i].r.x==x) printf("the same!\n");
+                       else printf("different!\n");
+               }
+               if(atom[i].r.y>=dim->y/2||-atom[i].r.y>dim->y/2)
+                       printf("FATAL: atom %d: y: %.20f (%.20f)\n",
+                              i,atom[i].r.y,dim->y/2);
+               if(atom[i].r.z>=dim->z/2||-atom[i].r.z>dim->z/2)
+                       printf("FATAL: atom %d: z: %.20f (%.20f)\n",
+                              i,atom[i].r.z,dim->z/2);
        }
-printf("%.30f\n",exchange->zeta);
-       
-       /* add to db_ij */
-       v3_add(&(exchange->db_ij),&(exchange->db_ij),&force);
-                               
+
        return 0;
 }
-