security ci
[physik/posic.git] / moldyn.c
index 4b58089..d74b391 100644 (file)
--- a/moldyn.c
+++ b/moldyn.c
@@ -35,6 +35,7 @@ int moldyn_usage(char **argv) {
        printf("--- physics options ---\n");
        printf("-T <temperature> [K] (%f)\n",MOLDYN_TEMP);
        printf("-t <timestep tau> [s] (%.15f)\n",MOLDYN_TAU);
+       printf("-C <cutoff radius> [m] (%.15f)\n",MOLDYN_CUTOFF);
        printf("-R <runs> (%d)\n",MOLDYN_RUNS);
        printf(" -- integration algo --\n");
        printf("  -I <number> (%d)\n",MOLDYN_INTEGRATE_DEFAULT);
@@ -57,6 +58,7 @@ int moldyn_parse_argv(t_moldyn *moldyn,int argc,char **argv) {
        int i;
        t_ho_params hop;
        t_lj_params ljp;
+       t_tersoff_params tp;
        double s,e;
 
        memset(moldyn,0,sizeof(t_moldyn));
@@ -80,10 +82,6 @@ int moldyn_parse_argv(t_moldyn *moldyn,int argc,char **argv) {
                                        moldyn->mwrite=atoi(argv[++i]);
                                        strncpy(moldyn->mfb,argv[++i],64);
                                        break;
-                               case 'D':
-                                       moldyn->dwrite=atoi(argv[++i]);
-                                       strncpy(moldyn->dfb,argv[++i],64);
-                                       break;
                                case 'S':
                                        moldyn->swrite=atoi(argv[++i]);
                                        strncpy(moldyn->sfb,argv[++i],64);
@@ -98,6 +96,9 @@ int moldyn_parse_argv(t_moldyn *moldyn,int argc,char **argv) {
                                case 't':
                                        moldyn->tau=atof(argv[++i]);
                                        break;
+                               case 'C':
+                                       moldyn->cutoff=atof(argv[++i]);
+                                       break;
                                case 'R':
                                        moldyn->time_steps=atoi(argv[++i]);
                                        break;
@@ -153,12 +154,12 @@ int moldyn_parse_argv(t_moldyn *moldyn,int argc,char **argv) {
        return 0;
 }
 
-int moldyn_log_init(t_moldyn *moldyn,void *v) {
+int moldyn_log_init(t_moldyn *moldyn) {
 
        moldyn->lvstat=0;
        t_visual *vis;
 
-       vis=v;
+       vis=&(moldyn->vis);
 
        if(moldyn->ewrite) {
                moldyn->efd=open(moldyn->efb,O_WRONLY|O_CREAT|O_TRUNC);
@@ -183,16 +184,6 @@ int moldyn_log_init(t_moldyn *moldyn,void *v) {
        if(moldyn->swrite)
                moldyn->lvstat|=MOLDYN_LVSTAT_SAVE;
 
-       if(moldyn->dwrite) {
-               moldyn->dfd=open(moldyn->dfb,O_WRONLY|O_CREAT|O_TRUNC);
-                if(moldyn->dfd<0) {
-                       perror("[moldyn] dfd open");
-                       return moldyn->dfd;
-               }
-               write(moldyn->dfd,moldyn,sizeof(t_moldyn));
-               moldyn->lvstat|=MOLDYN_LVSTAT_DUMP;
-       }
-
        if((moldyn->vwrite)&&(vis)) {
                moldyn->visual=vis;
                visual_init(vis,moldyn->vfb);
@@ -204,7 +195,7 @@ int moldyn_log_init(t_moldyn *moldyn,void *v) {
        return 0;
 }
 
-int moldyn_shutdown(t_moldyn *moldyn) {
+int moldyn_log_shutdown(t_moldyn *moldyn) {
 
        if(moldyn->efd) close(moldyn->efd);
        if(moldyn->mfd) close(moldyn->efd);
@@ -214,6 +205,33 @@ int moldyn_shutdown(t_moldyn *moldyn) {
        return 0;
 }
 
+int moldyn_init(t_moldyn *moldyn,int argc,char **argv) {
+
+       int ret;
+
+       ret=moldyn_parse_argv(moldyn,argc,argv);
+       if(ret<0) return ret;
+
+       ret=moldyn_log_init(moldyn);
+       if(ret<0) return ret;
+
+       rand_init(&(moldyn->random),NULL,1);
+       moldyn->random.status|=RAND_STAT_VERBOSE;
+
+       moldyn->status=0;
+
+       return 0;
+}
+
+int moldyn_shutdown(t_moldyn *moldyn) {
+
+       moldyn_log_shutdown(moldyn);
+       rand_close(&(moldyn->random));
+       free(moldyn->atom);
+
+       return 0;
+}
+
 int create_lattice(unsigned char type,int element,double mass,double lc,
                    int a,int b,int c,t_atom **atom) {
 
@@ -270,7 +288,7 @@ int destroy_lattice(t_atom *atom) {
        return 0;
 }
 
-int thermal_init(t_moldyn *moldyn,t_random *random) {
+int thermal_init(t_moldyn *moldyn) {
 
        /*
         * - gaussian distribution of velocities
@@ -282,8 +300,10 @@ int thermal_init(t_moldyn *moldyn,t_random *random) {
        double v,sigma;
        t_3dvec p_total,delta;
        t_atom *atom;
+       t_random *random;
 
        atom=moldyn->atom;
+       random=&(moldyn->random);
 
        /* gaussian distribution of velocities */
        v3_zero(&p_total);
@@ -402,9 +422,13 @@ double estimate_time_step(t_moldyn *moldyn,double nn_dist,double t) {
 int link_cell_init(t_moldyn *moldyn) {
 
        t_linkcell *lc;
+       int i;
 
        lc=&(moldyn->lc);
 
+       /* list log fd */
+       lc->listfd=open("/dev/null",O_WRONLY);
+
        /* partitioning the md cell */
        lc->nx=moldyn->dim.x/moldyn->cutoff;
        lc->x=moldyn->dim.x/lc->nx;
@@ -413,7 +437,14 @@ int link_cell_init(t_moldyn *moldyn) {
        lc->nz=moldyn->dim.z/moldyn->cutoff;
        lc->z=moldyn->dim.z/lc->nz;
 
-       lc->subcell=malloc(lc->nx*lc->ny*lc->nz*sizeof(t_list));
+       lc->cells=lc->nx*lc->ny*lc->nz;
+       lc->subcell=malloc(lc->cells*sizeof(t_list));
+
+       printf("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]));
 
        link_cell_update(moldyn);
        
@@ -434,13 +465,13 @@ int link_cell_update(t_moldyn *moldyn) {
        ny=lc->ny;
        nz=lc->nz;
 
-       for(i=0;i<nx*ny*nz;i++)
+       for(i=0;i<lc->cells;i++)
                list_destroy(&(moldyn->lc.subcell[i]));
        
-       for(count=0;count<moldyn->count;count++) {
-               i=atom[count].r.x/lc->x;
-               j=atom[count].r.y/lc->y;
-               k=atom[count].r.z/lc->z;
+       for(count=0;count<moedyn->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]));
        }
@@ -461,11 +492,12 @@ int link_cell_neighbour_index(t_moldyn *moldyn,int i,int j,int k,t_list *cell) {
        lc=&(moldyn->lc);
        nx=lc->nx;
        ny=lc->ny;
-       nx=lc->nz;
+       nz=lc->nz;
        count1=1;
        count2=27;
        a=nx*ny;
 
+
        cell[0]=lc->subcell[i+j*nx+k*a];
        for(ci=-1;ci<=1;ci++) {
                bx=0;
@@ -488,7 +520,7 @@ int link_cell_neighbour_index(t_moldyn *moldyn,int i,int j,int k,t_list *cell) {
                                        z=(z+nz)%nz;
                                        bz=1;
                                }
-                               if(!(x|y|z)) continue;
+                               if(!(ci|cj|ck)) continue;
                                if(bx|by|bz) {
                                        cell[--count2]=lc->subcell[x+y*nx+z*a];
                                }
@@ -499,6 +531,9 @@ int link_cell_neighbour_index(t_moldyn *moldyn,int i,int j,int k,t_list *cell) {
                }
        }
 
+       lc->dnlc=count2;
+       lc->countn=27;
+
        return count2;
 }
 
@@ -512,6 +547,8 @@ int link_cell_shutdown(t_moldyn *moldyn) {
        for(i=0;i<lc->nx*lc->ny*lc->nz;i++)
                list_shutdown(&(moldyn->lc.subcell[i]));
 
+       if(lc->listfd) close(lc->listfd);
+
        return 0;
 }
 
@@ -532,6 +569,9 @@ int moldyn_integrate(t_moldyn *moldyn) {
        int fd;
        char fb[128];
 
+       /* initialize linked cell method */
+       link_cell_init(moldyn);
+
        /* logging & visualization */
        e=moldyn->ewrite;
        m=moldyn->mwrite;
@@ -548,18 +588,10 @@ int moldyn_integrate(t_moldyn *moldyn) {
        moldyn->tau_square=moldyn->tau*moldyn->tau;
        moldyn->cutoff_square=moldyn->cutoff*moldyn->cutoff;
 
-       /* create the neighbour list */
-       link_cell_update(moldyn);
-
        /* calculate initial forces */
        moldyn->potential_force_function(moldyn);
 
        for(i=0;i<moldyn->time_steps;i++) {
-               /* show runs */
-               printf(".");
-
-               /* neighbour list update */
-               link_cell_update(moldyn);
 
                /* integration step */
                moldyn->integrate(moldyn);
@@ -590,18 +622,16 @@ int moldyn_integrate(t_moldyn *moldyn) {
                                        write(fd,moldyn->atom,
                                              moldyn->count*sizeof(t_atom));
                                }
+                               close(fd);
                        }       
                }
-               if(d) {
-                       if(!(i%d))
-                               write(moldyn->dfd,moldyn->atom,
-                                     moldyn->count*sizeof(t_atom));
-
-               }
                if(v) {
-                       if(!(i%v))
+                       if(!(i%v)) {
                                visual_atoms(moldyn->visual,i*moldyn->tau,
                                             moldyn->atom,moldyn->count);
+                               printf("\rsteps: %d",i);
+                               fflush(stdout);
+                       }
                }
        }
 
@@ -635,8 +665,16 @@ int velocity_verlet(t_moldyn *moldyn) {
                v3_add(&(atom[i].v),&(atom[i].v),&delta);
        }
 
+       /* neighbour list update */
+printf("list update ...\n");
+       link_cell_update(moldyn);
+printf("done\n");
+
        /* forces depending on chosen potential */
-       moldyn->potential_force_function(moldyn);
+printf("calc potential/force ...\n");
+       potential_force_calc(moldyn);
+       //moldyn->potential_force_function(moldyn);
+printf("done\n");
 
        for(i=0;i<count;i++) {
                /* again velocities */
@@ -654,9 +692,125 @@ int velocity_verlet(t_moldyn *moldyn) {
  * 
  */
 
+/* generic potential and force calculation */
+
+int potential_force_calc(t_moldyn *moldyn) {
+
+       int i,count;
+       t_atom *atom;
+       t_linkcell *lc;
+       t_list neighbour[27];
+       t_list *this;
+       double u;
+       unsigned char bc,bc3;
+       int countn,dnlc;
+
+       count=moldyn->count;
+       atom=moldyn->atom;
+       lc=&(moldyn->lc);
+
+       /* reset energy */
+       moldyn->energy=0.0;
+
+       for(i=0;i<count;i++) {
+       
+               /* reset force */
+               v3_zero(&(atom[i].f));
+
+               /* single particle potential/force */
+               if(atom[i].attr&ATOM_ATTR_1BP)
+                       moldyn->pf_func1b(moldyn,&(atom[i]));
+
+               /* 2 body pair potential/force */
+               if(atom[i].attr&(ATOM_ATTR_2BP|ATOM_ATTR_3BP)) {
+               
+                       link_cell_neighbour_index(moldyn,
+                               (atom[i].r.x+moldyn->dim.x/2)/lc->x,
+                               (atom[i].r.y+moldyn->dim.y/2)/lc->y,
+                               (atom[i].r.z+moldyn->dim.z/2)/lc->z,
+                               neighbour);
+
+                       countn=lc->countn;
+                       dnlc=lc->dnlc;
+
+                       for(j=0;j<countn;j++) {
+
+                               this=&(neighbour[j]);
+                               list_reset(this);
+
+                               if(this->start==NULL)
+                                       continue;
+
+                               bc=(j<dnlc)?0:1;
+
+                               do {
+                                       btom=this->current->data;
+
+                                       if(btom==&(atom[i]))
+                                               continue;
+
+                                       if((btom->attr&ATOM_ATTR_2BP)&
+                                          (atom[i].attr&ATOM_ATTR_2BP))
+                                               moldyn->pf_func2b(moldyn,
+                                                                 &(atom[i]),
+                                                                 btom,
+                                                                 bc);
+
+                                       /* 3 body potential/force */
+
+                                       if(!(atom[i].attr&ATOM_ATTR_3BP)||
+                                          !(btom->attr&ATOM_ATTR_3BP))
+                                               continue;
+
+                                       link_cell_neighbour_index(moldyn,
+                                          (btom->r.x+moldyn->dim.x/2)/lc->x,
+                                          (btom->r.y+moldyn->dim.y/2)/lc->y,
+                                          (btom->r.z+moldyn->dim.z/2)/lc->z,
+                                          neighbourk);
+
+                                       for(k=0;k<lc->countn;k++) {
+
+                                               thisk=&(neighbourk[k]);
+                                               list_reset(thisk);
+                                       
+                                               if(thisk->start==NULL)
+                                                       continue;
+
+                                               bck=(k<lc->dnlc)?0:1;
+
+                                               do {
+
+                       ktom=thisk->current->data;
+
+                       if(!(ktom->attr&ATOM_ATTR_3BP))
+                               continue;
+
+                       if(ktom==btom)
+                               continue;
+
+                       if(ktom==&(atom[i]))
+                               continue;
+
+                       moldyn->pf_func3b(moldyn,&(atom[i]),btom,ktom,bck);
+
+                                               } while(list_next(thisk)!=\
+                                                       L_NO_NEXT_ELEMENT);
+                                       
+                               } while(list_next(this)!=L_NO_NEXT_ELEMENT);
+                       }
+               }
+       }
+
+       return 0;
+}
+
+/*
+ * example potentials
+ */
+
 /* harmonic oscillator potential and force */
 
-int harmonic_oscillator(t_moldyn *moldyn) {
+int harmonic_oscillator(t_moldyn *moldyn,t_atom *ai,t_atom *aj,unsigned char bc)) {
 
        t_ho_params *params;
        t_atom *atom,*btom;
@@ -676,29 +830,43 @@ int harmonic_oscillator(t_moldyn *moldyn) {
        equi_dist=params->equilibrium_distance;
        count=moldyn->count;
 
+       /* reset energy counter */
        u=0.0;
+
        for(i=0;i<count;i++) {
+               /* reset force */
+               v3_zero(&(atom[i].f));
+
                /* determine cell + neighbours */
-               ni=atom[i].r.x/lc->x;
-               nj=atom[i].r.y/lc->y;
-               nk=atom[i].r.z/lc->z;
+               ni=(atom[i].r.x+(moldyn->dim.x/2))/lc->x;
+               nj=(atom[i].r.y+(moldyn->dim.y/2))/lc->y;
+               nk=(atom[i].r.z+(moldyn->dim.z/2))/lc->z;
                c=link_cell_neighbour_index(moldyn,ni,nj,nk,neighbour);
 
-               /* processing cell of atom i */
+               /*
+                * processing cell of atom i
+                * => no need to check for empty list (1 element at minimum)
+                */
                this=&(neighbour[0]);
-               list_reset(this); /* list has 1 element at minimum */
+               list_reset(this);
                do {
                        btom=this->current->data;
                        if(btom==&(atom[i]))
                                continue;
                        v3_sub(&distance,&(atom[i].r),&(btom->r));
                        d=v3_norm(&distance);
-                       u+=(0.5*sc*(d-equi_dist)*(d-equi_dist));
-                       v3_scale(&force,&distance,-sc*(1.0-(equi_dist/d)));
-                       v3_add(&(atom[i].f),&(atom[i].f),&force);
+                       if(d<=moldyn->cutoff) {
+                               u+=(0.5*sc*(d-equi_dist)*(d-equi_dist));
+                               v3_scale(&force,&distance,
+                                        -sc*(1.0-(equi_dist/d)));
+                               v3_add(&(atom[i].f),&(atom[i].f),&force);
+                       }
                } while(list_next(this)!=L_NO_NEXT_ELEMENT);
 
-               /* neighbours not doing boundary condition overflow */
+               /*
+                * direct neighbour cells
+                * => no boundary condition check necessary
+                */
                for(j=1;j<c;j++) {
                        this=&(neighbour[j]);
                        list_reset(this); /* there might not be a single atom */
@@ -720,7 +888,10 @@ int harmonic_oscillator(t_moldyn *moldyn) {
                        }
                }
 
-               /* neighbours due to boundary conditions */
+               /*
+                * indirect neighbour cells
+                * => check boundary conditions
+                */
                for(j=c;j<27;j++) {
                        this=&(neighbour[j]);
                        list_reset(this); /* check boundary conditions */
@@ -744,7 +915,7 @@ int harmonic_oscillator(t_moldyn *moldyn) {
                }
        }
 
-       moldyn->energy=u;
+       moldyn->energy=0.5*u;
 
        return 0;
 }
@@ -772,12 +943,17 @@ int lennard_jones(t_moldyn *moldyn) {
        sig6=params->sigma6;
        sig12=params->sigma12;
 
+       /* reset energy counter */
        u=0.0;
+
        for(i=0;i<count;i++) {
+               /* reset force */
+               v3_zero(&(atom[i].f));
+
                /* determine cell + neighbours */
-               ni=atom[i].r.x/lc->x;
-               nj=atom[i].r.y/lc->y;
-               nk=atom[i].r.z/lc->z;
+               ni=(atom[i].r.x+(moldyn->dim.x/2))/lc->x;
+               nj=(atom[i].r.y+(moldyn->dim.y/2))/lc->y;
+               nk=(atom[i].r.z+(moldyn->dim.z/2))/lc->z;
                c=link_cell_neighbour_index(moldyn,ni,nj,nk,neighbour);
 
                /* processing cell of atom i */
@@ -788,19 +964,22 @@ int lennard_jones(t_moldyn *moldyn) {
                        if(btom==&(atom[i]))
                                continue;
                        v3_sub(&distance,&(atom[i].r),&(btom->r));
-                       d=1.0/v3_absolute_square(&distance); /* 1/r^2 */
-                       h1=d*d;         /* 1/r^4 */
-                       h2*=d;          /* 1/r^6 */
-                       h1=h2*h2;       /* 1/r^12 */
-                       u+=eps*(sig12*h1-sig6*h2);
-                       h2*=d;          /* 1/r^8 */
-                       h1*=d;          /* 1/r^14 */
-                       h2*=6*sig6;
-                       h1*=12*sig12;
-                       d=-h1+h2;
-                       d*=eps;
-                       v3_scale(&force,&distance,d);
-                       v3_add(&(atom[i].f),&(atom[i].f),&force);
+                       d=v3_absolute_square(&distance);        /* 1/r^2 */
+                       if(d<=moldyn->cutoff_square) {
+                               d=1.0/d;        /* 1/r^2 */
+                               h2=d*d;         /* 1/r^4 */
+                               h2*=d;          /* 1/r^6 */
+                               h1=h2*h2;       /* 1/r^12 */
+                               u+=eps*(sig12*h1-sig6*h2);
+                               h2*=d;          /* 1/r^8 */
+                               h1*=d;          /* 1/r^14 */
+                               h2*=6*sig6;
+                               h1*=12*sig12;
+                               d=+h1-h2;
+                               d*=eps;
+                               v3_scale(&force,&distance,d);
+                               v3_add(&(atom[i].f),&(atom[i].f),&force);
+                       }
                } while(list_next(this)!=L_NO_NEXT_ELEMENT);
 
                /* neighbours not doing boundary condition overflow */
@@ -815,7 +994,7 @@ int lennard_jones(t_moldyn *moldyn) {
                                d=v3_absolute_square(&distance); /* r^2 */
                                if(d<=moldyn->cutoff_square) {
                                        d=1.0/d;        /* 1/r^2 */
-                                       h1=d*d;         /* 1/r^4 */
+                                       h2=d*d;         /* 1/r^4 */
                                        h2*=d;          /* 1/r^6 */
                                        h1=h2*h2;       /* 1/r^12 */
                                        u+=eps*(sig12*h1-sig6*h2);
@@ -823,7 +1002,7 @@ int lennard_jones(t_moldyn *moldyn) {
                                        h1*=d;          /* 1/r^14 */
                                        h2*=6*sig6;
                                        h1*=12*sig12;
-                                       d=-h1+h2;
+                                       d=+h1-h2;
                                        d*=eps;
                                        v3_scale(&force,&distance,d);
                                        v3_add(&(atom[i].f),&(atom[i].f),
@@ -847,7 +1026,7 @@ int lennard_jones(t_moldyn *moldyn) {
                                d=v3_absolute_square(&distance); /* r^2 */
                                if(d<=moldyn->cutoff_square) {
                                        d=1.0/d;        /* 1/r^2 */
-                                       h1=d*d;         /* 1/r^4 */
+                                       h2=d*d;         /* 1/r^4 */
                                        h2*=d;          /* 1/r^6 */
                                        h1=h2*h2;       /* 1/r^12 */
                                        u+=eps*(sig12*h1-sig6*h2);
@@ -855,7 +1034,7 @@ int lennard_jones(t_moldyn *moldyn) {
                                        h1*=d;          /* 1/r^14 */
                                        h2*=6*sig6;
                                        h1*=12*sig12;
-                                       d=-h1+h2;
+                                       d=+h1-h2;
                                        d*=eps;
                                        v3_scale(&force,&distance,d);
                                        v3_add(&(atom[i].f),&(atom[i].f),
@@ -867,8 +1046,367 @@ int lennard_jones(t_moldyn *moldyn) {
                }
        }
 
-       moldyn->energy=u;
+       moldyn->energy=0.5*u;
+       
+       return 0;
+}
+
+/* tersoff potential & force for 2 sorts of atoms */
+
+int tersoff(t_moldyn *moldyn) {
+
+       t_tersoff_params *params;
+       t_atom *atom,*btom,*ktom;
+       t_linkcell *lc;
+       t_list *this,*thisk,neighbour[27],neighbourk[27];
+       int i,j,k,c,ck;
+       int count;
+       double u;
+       int ni,nj,nk;
+       int ki,kj,kk;
+       
+
+       params=moldyn->pot_params;
+       atom=moldyn->atom;
+       lc=&(moldyn->lc);
+       count=moldyn->count;
        
+       /* reset energy counter */
+       u=0.0;
+
+       for(i=0;i<count;i++) {
+               /* reset force */
+               v3_zero(&(atom[i].f));
+
+               /* determin cell neighbours */
+               ni=(atom[i].r.x+(moldyn->dim.x/2))/lc->x;
+               nj=(atom[i].r.y+(moldyn->dim.y/2))/lc->y;
+               nk=(atom[i].r.z+(moldyn->dim.z/2))/lc->z;
+               c=link_cell_neighbour_index(moldyn,ni,nj,nk,neighbour);
+
+               /*
+                * processing cell of atom i
+                * => no need to check for empty list (1 element at minimum)
+                */
+               this=&(neighbour[0]);
+               list_reset(this);
+               do {
+                       btom=this->current->data;
+                       if(btom==&(atom[i]))
+                               continue;
+
+                       /* 2 body stuff */
+
+                       /* we need: f_c, df_c, f_r, df_r */
+
+                       v3_sub(&dist_ij,btom,&(atom[i]));
+                       d_ij=v3_norm(&dist_ij);
+                       if(d_ij<=S) {
+
+                               /* determine the tersoff parameters */
+                               if(atom[i].element!=btom->element) {
+                               S=sqrt(TERSOFF_S[e1]*TERSOFF_S[e2]);
+                               R=R_m;
+                               A=;
+                               lambda=;
+                               B=;
+                               mu=;
+                               chi=;
+                               beta=;
+                               betaN=;
+
+                               if(d_ij<=R) {
+                                       df_r=-lambda*A*exp(-lambda*d_ij)/d_ij;
+                                       v3_scale(&force,&dist_ij,df_r);
+                                       v3_add(&(atom[i].f),&(atom[i].f),
+                                               &force);
+                               }
+                               else {
+                                       s_r=S-R;
+                                       arg1=PI*(d_ij-R)/s_r;
+                                       f_c=0.5+0.5*cos(arg1);
+                                       df_c=-0.5*sin(arg1)*(PI/(s_r*d_ij));
+                                       f_r=A*exp(-lambda*d_ij);
+                                       df_r=-lambda*f_r/d_ij;
+                                       scale=df_c*f_r+df_r*f_c;
+                                       v3_scale(&force,&dist_ij,scale);
+                                       v3_add(&(atom[i].f),&(atom[i].f),
+                                              &force);
+                               }
+                       }
+                       else 
+                               continue;               
+
+                       
+                       /* end 2 body stuff */ 
+
+                       /* determine cell neighbours of btom */
+                       ki=(btom->r.x+(moldyn->dim.x/2))/lc->x;
+                       kj=(btom->r.y+(moldyn->dim.y/2))/lc->y;
+                       kk=(btom->r.z+(moldyn->dim.z/2))/lc->z;
+                       ck=link_cell_neighbour_index(moldyn,ki,kj,kk,
+                                                    neighbourk);
+
+                       /* go for zeta - 3 body stuff! */
+                       zeta=0.0;
+                       d_ij2=d_ij*d_ij;
+
+                       /* cell of btom */
+                       thisk=&(neighbourk[0]);
+                       list_reset(thisk);
+                       do {
+                               ktom=thisk->current->data;
+                               if(ktom==btom)
+                                       continue;
+                               if(ktom==&(atom[i]))
+                                       continue;
+                               
+                               /* 3 body stuff (1) */
+                               
+                               v3_sub(&dist_ik,ktom,&(atom[i]));
+                               d_ik=v3_norm(&dist_ik);
+                               if(d_ik<=Sik) {
+
+                               Rik=;
+                               Sik=;
+                               Aik=;
+                               lambda_ik=;
+                               Bik=;
+                               mu_ik=;
+                               omega_ik=;
+                               c_i=;
+                               d_i=;
+                               h_i=;
+                       
+
+                                       if(d_ik<=Rik) {
+                                               f_cik=1.0;
+                                               df_cik=0.0;
+                                       }
+                                       else {
+                                               sik_rik=Sik-Rik;
+                                               arg1ik=PI*(d_ik-Rik)/sik_rik;
+                                               f_cik=0.5+0.5*cos(arg1ik);
+                                               df_cik=-0.5*sin(arg1ik)* \
+                                                      (PI/(sik_rik*d_ik));
+                                               f_rik=Aik*exp(-lambda_ik*d_ik);
+                                               f_aik=-Bik*exp(-mu_ik*d_ik);
+                                       }
+                       
+                                       v3_sub(&distance_jk,ktom,btom);
+                                       cos_theta=(d_ij2+d_ik*d_ik-d_jk*d_jk)/\
+                                                 (2*d_ij*d_ik);
+                                       sin_theta=sqrt(1.0/\
+                                                 (cos_theta*cos_theta));
+                                       theta=arccos(cos_theta);
+
+                                       
+                               }
+                               else
+                                       continue;
+
+                               /* end 3 body stuff (1) */
+
+
+                       } while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+
+                       /* direct neighbours of btom cell */
+                       for(k=1;k<ck;k++) {
+                               thisk=&(neighbourk[k]);
+                               list_reset(thisk);
+                               if(thisk->start!=NULL) {
+
+                               do {
+                                       ktom=thisk->current->data;
+                                       if(ktom==&(atom[i]))
+                                               continue;
+
+                               /* 3 body stuff (2) */
+
+                               } while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+
+                               }
+                       }
+
+                       /* indirect neighbours of btom cell */
+                       for(k=ck;k<27;k++) {
+                               thisk=&(neighbourk[k]);
+                               list_reset(thisk);
+                               if(thisk->start!=NULL) {
+
+                               do {
+                                       ktom=thisk->current->data;
+                                       if(ktom==&(atom[i]))
+                                               continue;
+
+                               /* 3 body stuff */
+
+                               } while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+
+                               }
+                       }
+
+
+               } while(list_next(this)!=L_NO_NEXT_ELEMENT);
+
+               /*
+                * direct neighbour cells of atom i
+                */
+               for(j=1;j<c;j++) {
+                       this=&(neighbour[j]);
+                       list_reset(this);
+                       if(this->start!=NULL) {
+
+                       do {
+                               btom=this->current->data;
+
+                               /* 2 body stuff */
+
+
+                       /* determine cell neighbours of btom */
+                       ki=(btom->r.x+(moldyn->dim.x/2))/lc->x;
+                       kj=(btom->r.y+(moldyn->dim.y/2))/lc->y;
+                       kk=(btom->r.z+(moldyn->dim.z/2))/lc->z;
+                       ck=link_cell_neighbour_index(moldyn,ki,kj,kk,
+                                                    neighbourk);
+
+                       /* cell of btom */
+                       thisk=&(neighbourk[0]);
+                       list_reset(thisk);
+                       do {
+                               ktom=thisk->current->data;
+                               if(ktom==btom)
+                                       continue;
+                               if(ktom==&(atom[i]))
+                                       continue;
+                               
+                               /* 3 body stuff (1) */
+
+                       } while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+
+                       /* direct neighbours of btom cell */
+                       for(k=1;k<ck;k++) {
+                               thisk=&(neighbourk[k]);
+                               list_reset(thisk);
+                               if(thisk->start!=NULL) {
+
+                               do {
+                                       ktom=thisk->current->data;
+                                       if(ktom==&(atom[i]))
+                                               continue;
+
+                               /* 3 body stuff (2) */
+
+                               } while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+
+                               }
+                       }
+
+                       /* indirect neighbours of btom cell */
+                       for(k=ck;k<27;k++) {
+                               thisk=&(neighbourk[k]);
+                               list_reset(thisk);
+                               if(thisk->start!=NULL) {
+
+                               do {
+                                       ktom=thisk->current->data;
+                                       if(ktom==&(atom[i]))
+                                               continue;
+
+                               /* 3 body stuff (3) */
+
+                               } while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+
+                               }
+                       }
+
+
+                       } while(list_next(this)!=L_NO_NEXT_ELEMENT);
+
+                       }
+               }
+
+               /*
+                * indirect neighbour cells of atom i
+                */
+               for(j=c;j<27;j++) {
+                       this=&(neighbour[j]);
+                       list_reset(this);
+                       if(this->start!=NULL) {
+
+                       do {
+                               btom=this->current->data;
+
+                               /* 2 body stuff */
+
+
+                       /* determine cell neighbours of btom */
+                       ki=(btom->r.x+(moldyn->dim.x/2))/lc->x;
+                       kj=(btom->r.y+(moldyn->dim.y/2))/lc->y;
+                       kk=(btom->r.z+(moldyn->dim.z/2))/lc->z;
+                       ck=link_cell_neighbour_index(moldyn,ki,kj,kk,
+                                                    neighbourk);
+
+                       /* cell of btom */
+                       thisk=&(neighbourk[0]);
+                       list_reset(thisk);
+                       do {
+                               ktom=thisk->current->data;
+                               if(ktom==btom)
+                                       continue;
+                               if(ktom==&(atom[i]))
+                                       continue;
+                               
+                               /* 3 body stuff (1) */
+
+                       } while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+
+                       /* direct neighbours of btom cell */
+                       for(k=1;k<ck;k++) {
+                               thisk=&(neighbourk[k]);
+                               list_reset(thisk);
+                               if(thisk->start!=NULL) {
+
+                               do {
+                                       ktom=thisk->current->data;
+                                       if(ktom==&(atom[i]))
+                                               continue;
+
+                               /* 3 body stuff (2) */
+
+                               } while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+
+                               }
+                       }
+
+                       /* indirect neighbours of btom cell */
+                       for(k=ck;k<27;k++) {
+                               thisk=&(neighbourk[k]);
+                               list_reset(thisk);
+                               if(thisk->start!=NULL) {
+
+                               do {
+                                       ktom=thisk->current->data;
+                                       if(ktom==&(atom[i]))
+                                               continue;
+
+                               /* 3 body stuff (3) */
+
+                               } while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+
+                               }
+                       }
+
+
+                       } while(list_next(this)!=L_NO_NEXT_ELEMENT);
+
+                       }
+               }
+               
+       }
+
+       moldyn->energy=0.5*u;
+
        return 0;
 }