nearly finished tersoff 2 body part and new api
[physik/posic.git] / moldyn.c
index 1b52a56..9f88211 100644 (file)
--- a/moldyn.c
+++ b/moldyn.c
@@ -58,6 +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));
@@ -81,10 +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);
@@ -187,16 +184,6 @@ int moldyn_log_init(t_moldyn *moldyn) {
        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);
@@ -245,7 +232,7 @@ int moldyn_shutdown(t_moldyn *moldyn) {
        return 0;
 }
 
-int create_lattice(unsigned char type,int element,double mass,double lc,
+int create_lattice(u8 type,int element,double mass,double lc,
                    int a,int b,int c,t_atom **atom) {
 
        int count;
@@ -481,7 +468,7 @@ int link_cell_update(t_moldyn *moldyn) {
        for(i=0;i<lc->cells;i++)
                list_destroy(&(moldyn->lc.subcell[i]));
        
-       for(count=0;count<moldyn->count;count++) {
+       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;
@@ -500,7 +487,7 @@ int link_cell_neighbour_index(t_moldyn *moldyn,int i,int j,int k,t_list *cell) {
        int ci,cj,ck;
        int nx,ny,nz;
        int x,y,z;
-       unsigned char bx,by,bz;
+       u8 bx,by,bz;
 
        lc=&(moldyn->lc);
        nx=lc->nx;
@@ -544,6 +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;
 }
 
@@ -632,14 +622,9 @@ 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)) {
                                visual_atoms(moldyn->visual,i*moldyn->tau,
@@ -687,7 +672,8 @@ printf("done\n");
 
        /* forces depending on chosen potential */
 printf("calc potential/force ...\n");
-       moldyn->potential_force_function(moldyn);
+       potential_force_calc(moldyn);
+       //moldyn->potential_force_function(moldyn);
 printf("done\n");
 
        for(i=0;i<count;i++) {
@@ -706,309 +692,304 @@ printf("done\n");
  * 
  */
 
-/* harmonic oscillator potential and force */
+/* generic potential and force calculation */
 
-int harmonic_oscillator(t_moldyn *moldyn) {
+int potential_force_calc(t_moldyn *moldyn) {
 
-       t_ho_params *params;
-       t_atom *atom,*btom;
+       int i,count;
+       t_atom *atom;
        t_linkcell *lc;
-       t_list *this,neighbour[27];
-       int i,j,c;
-       int count;
-       t_3dvec force,distance;
-       double d,u;
-       double sc,equi_dist;
-       int ni,nj,nk;
+       t_list neighbour[27];
+       t_list *this;
+       double u;
+       u8 bc,bc3;
+       int countn,dnlc;
 
-       params=moldyn->pot_params;
+       count=moldyn->count;
        atom=moldyn->atom;
        lc=&(moldyn->lc);
-       sc=params->spring_constant;
-       equi_dist=params->equilibrium_distance;
-       count=moldyn->count;
 
-       /* reset energy counter */
-       u=0.0;
+       /* reset energy */
+       moldyn->energy=0.0;
 
        for(i=0;i<count;i++) {
+       
                /* reset force */
                v3_zero(&(atom[i].f));
 
-               /* determine 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);
+               /* single particle potential/force */
+               if(atom[i].attr&ATOM_ATTR_1BP)
+                       moldyn->pf_func1b(moldyn,&(atom[i]));
 
-               /*
-                * 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;
-                       v3_sub(&distance,&(atom[i].r),&(btom->r));
-                       d=v3_norm(&distance);
-                       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);
+               /* 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);
 
-               /*
-                * 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 */
-                       if(this->start!=NULL) {
+                       countn=lc->countn;
+                       dnlc=lc->dnlc;
 
-                       do {
-                               btom=this->current->data;
-                               v3_sub(&distance,&(atom[i].r),&(btom->r));
-                               d=v3_norm(&distance);
-                               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);
+                       for(j=0;j<countn;j++) {
 
-                       }
-               }
+                               this=&(neighbour[j]);
+                               list_reset(this);
 
-               /*
-                * indirect neighbour cells
-                * => check boundary conditions
-                */
-               for(j=c;j<27;j++) {
-                       this=&(neighbour[j]);
-                       list_reset(this); /* check boundary conditions */
-                       if(this->start!=NULL) {
+                               if(this->start==NULL)
+                                       continue;
 
-                       do {
-                               btom=this->current->data;
-                               v3_sub(&distance,&(atom[i].r),&(btom->r));
-                               v3_per_bound(&distance,&(moldyn->dim));
-                               d=v3_norm(&distance);
-                               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);
+                               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);
                        }
                }
        }
 
-       moldyn->energy=0.5*u;
+       return 0;
+}
+
+/*
+ * periodic boundayr checking
+ */
+
+int check_per_bound(t_moldyn *moldyn,t_3dvec *a) {
+       
+       double x,y,z;
+
+       x=0.5*dim->x;
+       y=0.5*dim->y;
+       z=0.5*dim->z;
+
+       if(moldyn->MOLDYN_ATTR_PBX)
+               if(a->x>=x) a->x-=dim->x;
+               else if(-a->x>x) a->x+=dim->x;
+       if(moldyn->MOLDYN_ATTR_PBY)
+               if(a->y>=y) a->y-=dim->y;
+               else if(-a->y>y) a->y+=dim->y;
+       if(moldyn->MOLDYN_ATTR_PBZ)
+               if(a->z>=z) a->z-=dim->z;
+               else if(-a->z>z) a->z+=dim->z;
+
+       return 0;
+}
+        
+
+/*
+ * example potentials
+ */
+
+/* harmonic oscillator potential and force */
+
+int harmonic_oscillator(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc)) {
+
+       t_ho_params *params;
+       t_3dvec force,distance;
+       double d;
+       double sc,equi_dist;
+
+       params=moldyn->pot2b_params;
+       sc=params->spring_constant;
+       equi_dist=params->equilibrium_distance;
+
+       v3_sub(&distance,&(ai->r),&(aj->r);
+       
+       v3_per_bound(&distance,&(moldyn->dim));
+       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)));
+               v3_add(&(ai->f),&(ai->f),&force);
+       }
 
        return 0;
 }
 
 /* lennard jones potential & force for one sort of atoms */
  
-int lennard_jones(t_moldyn *moldyn) {
+int lennard_jones(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 
        t_lj_params *params;
-       t_atom *atom,*btom;
-       t_linkcell *lc;
-       t_list *this,neighbour[27];
-       int i,j,c;
-       int count;
        t_3dvec force,distance;
        double d,h1,h2,u;
        double eps,sig6,sig12;
-       int ni,nj,nk;
 
        params=moldyn->pot_params;
-       atom=moldyn->atom;
-       lc=&(moldyn->lc);
-       count=moldyn->count;
        eps=params->epsilon4;
        sig6=params->sigma6;
        sig12=params->sigma12;
 
-       /* reset energy counter */
-       u=0.0;
+       v3_sub(&distance,&(ai->r),&(aj->r));
+       if(bc) check_per_bound(moldyn,&distance);
+       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 */
+               /* energy is eps*..., but we will add this twice ... */
+               moldyn->energy+=0.5*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(&(ai->f),&(aj->f),&force);
+       }
 
-       for(i=0;i<count;i++) {
-               /* reset force */
-               v3_zero(&(atom[i].f));
+       return 0;
+}
 
-               /* determine 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 */
-               this=&(neighbour[0]);
-               list_reset(this); /* list has 1 element at minimum */
-               do {
-                       btom=this->current->data;
-                       if(btom==&(atom[i]))
-                               continue;
-                       v3_sub(&distance,&(atom[i].r),&(btom->r));
-                       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);
+/*
+ * tersoff potential & force for 2 sorts of atoms
+ */
 
-               /* neighbours not doing boundary condition overflow */
-               for(j=1;j<c;j++) {
-                       this=&(neighbour[j]);
-                       list_reset(this); /* there might not be a single atom */
-                       if(this->start!=NULL) {
+/* tersoff 2 body part */
 
-                       do {
-                               btom=this->current->data;
-                               v3_sub(&distance,&(atom[i].r),&(btom->r));
-                               d=v3_absolute_square(&distance); /* 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);
-                               
-                       }
-               }
+int tersoff_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 
-               /* neighbours due to boundary conditions */
-               for(j=c;j<27;j++) {
-                       this=&(neighbour[j]);
-                       list_reset(this); /* check boundary conditions */
-                       if(this->start!=NULL) {
+       t_tersoff_params *params;
+       t_3dvec dist_ij;
+       double d_ij;
 
-                       do {
-                               btom=this->current->data;
-                               v3_sub(&distance,&(atom[i].r),&(btom->r));
-                               v3_per_bound(&distance,&(moldyn->dim));
-                               d=v3_absolute_square(&distance); /* 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);
+       params=moldyn->pot_params;
+       
+       /*
+        * we need: f_c, df_c, f_r, df_r
+        *
+        * therefore we need: R, S
+        */
 
-                       }
+       v3_sub(&dist_ij,&(ai->r),&(aj->r));
+
+       if(bc) check_per_bound(moldyn,&dist_ij);
+
+       if(ai->bnum==aj->bnum) {
+               S=params->S[ai->bnum];
+               R=params->R[ai->bnum];
+       }
+       else {
+               S=params->Smixed;
+               R=params->Rmixed;
+       }
+
+       d_ij=v3_norm(&dist_ij);
+
+       if(d_ij<=S) {
+               f_r=A*exp(-lamda*d_ij);
+               df_r=-lambda*f_r/d_ij;
+               if(d_ij<R) {
+                       /* f_c = 1, df_c = 0 */
+                       v3_scale(&force,&dist_ij,df_r);
+               }
+               else {
+                       s_r=S-R;
+                       arg=PI*(d_ij-R)/s_r;
+                       f_c=0.5+0.5*cos(arg);
+                       df_c=-0.5*sin(arg)*(PI/(s_r*d_ij));
+                       scale=df_c*f_r+df_r*f_c;
+                       v3_scale(&force,&dist_ij,scale);
+                       v3_add(&(ai->f),&(ai->f),&force);
                }
+               moldyn->energy+=(f_r*f_c);
        }
 
-       moldyn->energy=0.5*u;
-       
        return 0;
 }
 
-/* tersoff potential & force for 2 sorts of atoms */
+/* tersoff 3 body part */
 
-int tersoff(t_moldyn *moldyn) {
+int tersoff(t_moldyn *moldyn,t_atom *ai,t_atom *aj,t_atom *ak,u8 bc,u8 bck) {
 
        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;
-       
+       t_3dvec dist_ij;
+       double d_ij;
 
        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 */
+       /* 2 body part of the tersoff potential */
 
-                       v3_sub(&dist_ij,btom,&(atom[i]));
-                       d_ij=v3_norm(&dist_ij);
-                       if(d_ij<=S) {
+       v3_sub(&dist_ij,&(ai->r),&(aj->r));
+       if(bc) check_per_bound(moldyn,&dist_ij);
+       d_ij=v3_norm(&dist_ij);
+               if(d_ij<=S) {
 
-                               S=;
-                               R=;
+                               /* 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) {
-                                       f_c=1.0;
-                                       df_c=0.0;
+                                       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;
@@ -1016,7 +997,11 @@ int tersoff(t_moldyn *moldyn) {
                                        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);
-                                       f_a=-B*exp(-mu*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 
@@ -1032,6 +1017,10 @@ int tersoff(t_moldyn *moldyn) {
                        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);
@@ -1044,12 +1033,47 @@ int tersoff(t_moldyn *moldyn) {
                                
                                /* 3 body stuff (1) */
                                
-                               theta_ijk=;
-                               sin_theta=;
-                               cos_theta=;
-                               hi_cos=;
-                               hi_cos_square=;
+                               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) */