nur foo ...
[physik/posic.git] / moldyn.c
index d33de02..881f0b6 100644 (file)
--- a/moldyn.c
+++ b/moldyn.c
 #include <math.h>
 
 #include "moldyn.h"
+#include "report/report.h"
 
 int moldyn_init(t_moldyn *moldyn,int argc,char **argv) {
 
+       printf("[moldyn] init\n");
+
        memset(moldyn,0,sizeof(t_moldyn));
 
        rand_init(&(moldyn->random),NULL,1);
@@ -30,6 +33,7 @@ int moldyn_init(t_moldyn *moldyn,int argc,char **argv) {
 int moldyn_shutdown(t_moldyn *moldyn) {
 
        printf("[moldyn] shutdown\n");
+
        moldyn_log_shutdown(moldyn);
        link_cell_shutdown(moldyn);
        rand_close(&(moldyn->random));
@@ -40,12 +44,16 @@ int moldyn_shutdown(t_moldyn *moldyn) {
 
 int set_int_alg(t_moldyn *moldyn,u8 algo) {
 
+       printf("[moldyn] integration algorithm: ");
+
        switch(algo) {
                case MOLDYN_INTEGRATE_VERLET:
                        moldyn->integrate=velocity_verlet;
+                       printf("velocity verlet\n");
                        break;
                default:
                        printf("unknown integration algorithm: %02x\n",algo);
+                       printf("unknown\n");
                        return -1;
        }
 
@@ -56,6 +64,8 @@ int set_cutoff(t_moldyn *moldyn,double cutoff) {
 
        moldyn->cutoff=cutoff;
 
+       printf("[moldyn] cutoff [A]: %f\n",moldyn->cutoff);
+
        return 0;
 }
 
@@ -63,6 +73,8 @@ int set_temperature(t_moldyn *moldyn,double t_ref) {
 
        moldyn->t_ref=t_ref;
 
+       printf("[moldyn] temperature: %f\n",moldyn->t_ref);
+
        return 0;
 }
 
@@ -70,6 +82,8 @@ int set_pressure(t_moldyn *moldyn,double p_ref) {
 
        moldyn->p_ref=p_ref;
 
+       printf("[moldyn] pressure: %f\n",moldyn->p_ref);
+
        return 0;
 }
 
@@ -79,6 +93,18 @@ int set_pt_scale(t_moldyn *moldyn,u8 ptype,double ptc,u8 ttype,double ttc) {
        moldyn->t_tc=ttc;
        moldyn->p_tc=ptc;
 
+       printf("[moldyn] p/t scaling:\n");
+
+       printf("  p: %s",ptype?"yes":"no ");
+       if(ptype)
+               printf(" | type: %02x | factor: %f",ptype,ptc);
+       printf("\n");
+
+       printf("  t: %s",ttype?"yes":"no ");
+       if(ttype)
+               printf(" | type: %02x | factor: %f",ttype,ttc);
+       printf("\n");
+
        return 0;
 }
 
@@ -96,12 +122,15 @@ int set_dim(t_moldyn *moldyn,double x,double y,double z,u8 visualize) {
                moldyn->vis.dim.z=z;
        }
 
+       moldyn->dv=0.000001*moldyn->volume;
+
        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");
+       printf("  visualize simulation box: %s\n",visualize?"yes":"no");
+       printf("  delta volume (pressure calc): %f\n",moldyn->dv);
 
        return 0;
 }
@@ -115,6 +144,8 @@ int set_nn_dist(t_moldyn *moldyn,double dist) {
 
 int set_pbc(t_moldyn *moldyn,u8 x,u8 y,u8 z) {
 
+       printf("[moldyn] periodic boundary conditions:\n");
+
        if(x)
                moldyn->status|=MOLDYN_STAT_PBX;
 
@@ -124,6 +155,10 @@ int set_pbc(t_moldyn *moldyn,u8 x,u8 y,u8 z) {
        if(z)
                moldyn->status|=MOLDYN_STAT_PBZ;
 
+       printf("  x: %s\n",x?"yes":"no");
+       printf("  y: %s\n",y?"yes":"no");
+       printf("  z: %s\n",z?"yes":"no");
+
        return 0;
 }
 
@@ -165,12 +200,22 @@ int moldyn_set_log_dir(t_moldyn *moldyn,char *dir) {
 
        return 0;
 }
+
+int moldyn_set_report(t_moldyn *moldyn,char *author,char *title) {
+
+       strncpy(moldyn->rauthor,author,63);
+       strncpy(moldyn->rtitle,title,63);
+
+       return 0;
+}
        
 int moldyn_set_log(t_moldyn *moldyn,u8 type,int timer) {
 
        char filename[128];
        int ret;
 
+       printf("[moldyn] set log: ");
+
        switch(type) {
                case LOG_TOTAL_ENERGY:
                        moldyn->ewrite=timer;
@@ -183,6 +228,7 @@ int moldyn_set_log(t_moldyn *moldyn,u8 type,int timer) {
                                return moldyn->efd;
                        }
                        dprintf(moldyn->efd,"# total energy log file\n");
+                       printf("total energy (%d)\n",timer);
                        break;
                case LOG_TOTAL_MOMENTUM:
                        moldyn->mwrite=timer;
@@ -195,9 +241,11 @@ int moldyn_set_log(t_moldyn *moldyn,u8 type,int timer) {
                                return moldyn->mfd;
                        }
                        dprintf(moldyn->efd,"# total momentum log file\n");
+                       printf("total momentum (%d)\n",timer);
                        break;
                case SAVE_STEP:
                        moldyn->swrite=timer;
+                       printf("save file (%d)\n",timer);
                        break;
                case VISUAL_STEP:
                        moldyn->vwrite=timer;
@@ -206,9 +254,32 @@ int moldyn_set_log(t_moldyn *moldyn,u8 type,int timer) {
                                printf("[moldyn] visual init failure\n");
                                return ret;
                        }
+                       printf("visual file (%d)\n",timer);
+                       break;
+               case CREATE_REPORT:
+                       snprintf(filename,127,"%s/report.tex",moldyn->vlsdir);
+                       moldyn->rfd=open(filename,
+                                        O_WRONLY|O_CREAT|O_EXCL,
+                                        S_IRUSR|S_IWUSR);
+                       if(moldyn->rfd<0) {
+                               perror("[moldyn] report fd open");      
+                               return moldyn->rfd;
+                       }
+                       snprintf(filename,127,"%s/plot.scr",moldyn->vlsdir);
+                       moldyn->pfd=open(filename,
+                                        O_WRONLY|O_CREAT|O_EXCL,
+                                        S_IRUSR|S_IWUSR);
+                       if(moldyn->pfd<0) {
+                               perror("[moldyn] plot fd open");
+                               return moldyn->pfd;
+                       }
+                       dprintf(moldyn->rfd,report_start,
+                               moldyn->rauthor,moldyn->rtitle);
+                       dprintf(moldyn->pfd,plot_script);
+                       close(moldyn->pfd);
                        break;
                default:
-                       printf("[moldyn] unknown log mechanism: %02x\n",type);
+                       printf("unknown log type: %02x\n",type);
                        return -1;
        }
 
@@ -217,9 +288,23 @@ int moldyn_set_log(t_moldyn *moldyn,u8 type,int timer) {
 
 int moldyn_log_shutdown(t_moldyn *moldyn) {
 
+       char sc[256];
+
        printf("[moldyn] log shutdown\n");
        if(moldyn->efd) close(moldyn->efd);
        if(moldyn->mfd) close(moldyn->mfd);
+       if(moldyn->rfd) {
+               dprintf(moldyn->rfd,report_end);
+               close(moldyn->rfd);
+               snprintf(sc,255,"cd %s && gnuplot plot.scr",moldyn->vlsdir);
+               system(sc);
+               snprintf(sc,255,"cd %s && pdflatex report",moldyn->vlsdir);
+               system(sc);
+               snprintf(sc,255,"cd %s && pdflatex report",moldyn->vlsdir);
+               system(sc);
+               snprintf(sc,255,"cd %s && dvipdf report",moldyn->vlsdir);
+               system(sc);
+       }
        if(&(moldyn->vis)) visual_tini(&(moldyn->vis));
 
        return 0;
@@ -242,6 +327,7 @@ int create_lattice(t_moldyn *moldyn,u8 type,double lc,int element,double mass,
        count=moldyn->count;
 
        /* how many atoms do we expect */
+       if(type==CUBIC) new*=1;
        if(type==FCC) new*=4;
        if(type==DIAMOND) new*=8;
 
@@ -257,8 +343,14 @@ int create_lattice(t_moldyn *moldyn,u8 type,double lc,int element,double mass,
        v3_zero(&origin);
 
        switch(type) {
+               case CUBIC:
+                       origin.x=0.5*lc;
+                       origin.y=0.5*lc;
+                       origin.z=0.5*lc;
+                       ret=cubic_init(a,b,c,lc,atom,&origin);
+                       break;
                case FCC:
-                       ret=fcc_init(a,b,c,lc,atom,&origin);
+                       ret=fcc_init(a,b,c,lc,atom,NULL);
                        break;
                case DIAMOND:
                        ret=diamond_init(a,b,c,lc,atom,&origin);
@@ -292,6 +384,44 @@ int create_lattice(t_moldyn *moldyn,u8 type,double lc,int element,double mass,
        return ret;
 }
 
+/* cubic init */
+int cubic_init(int a,int b,int c,double lc,t_atom *atom,t_3dvec *origin) {
+
+       int count;
+       t_3dvec r;
+       int i,j,k;
+       t_3dvec o;
+
+       count=0;
+       if(origin)
+               v3_copy(&o,origin);
+       else
+               v3_zero(&o);
+
+       r.x=o.x;
+       for(i=0;i<a;i++) {
+               r.y=o.y;
+               for(j=0;j<b;j++) {
+                       r.z=o.z;
+                       for(k=0;k<c;k++) {
+                               v3_copy(&(atom[count].r),&r);
+                               count+=1;
+                               r.z+=lc;
+                       }
+                       r.y+=lc;
+               }
+               r.x+=lc;
+       }
+
+       for(i=0;i<count;i++) {
+               atom[i].r.x-=(a*lc)/2.0;
+               atom[i].r.y-=(b*lc)/2.0;
+               atom[i].r.z-=(c*lc)/2.0;
+       }
+
+       return count;
+}
+
 /* fcc lattice init */
 int fcc_init(int a,int b,int c,double lc,t_atom *atom,t_3dvec *origin) {
 
@@ -429,6 +559,8 @@ int thermal_init(t_moldyn *moldyn,u8 equi_init) {
        atom=moldyn->atom;
        random=&(moldyn->random);
 
+       printf("[moldyn] thermal init (equi init: %s)\n",equi_init?"yes":"no");
+
        /* gaussian distribution of velocities */
        v3_zero(&p_total);
        for(i=0;i<moldyn->count;i++) {
@@ -462,17 +594,9 @@ int thermal_init(t_moldyn *moldyn,u8 equi_init) {
 
 double temperature_calc(t_moldyn *moldyn) {
 
-       double double_ekin;
-       int i;
-       t_atom *atom;
-
-       atom=moldyn->atom;
-
-       for(i=0;i<moldyn->count;i++)
-               double_ekin+=atom[i].mass*v3_absolute_square(&(atom[i].v));
+       /* assume up to date kinetic energy, which is 3/2 N k_B T */
 
-       /* kinetic energy = 3/2 N k_B T */
-       moldyn->t=double_ekin/(3.0*K_BOLTZMANN*moldyn->count);
+       moldyn->t=(2.0*moldyn->ekin)/(3.0*K_BOLTZMANN*moldyn->count);
 
        return moldyn->t;
 }
@@ -538,27 +662,127 @@ int scale_velocity(t_moldyn *moldyn,u8 equi_init) {
        return 0;
 }
 
+double ideal_gas_law_pressure(t_moldyn *moldyn) {
+
+       double p;
+
+       p=moldyn->count*moldyn->t*K_BOLTZMANN/moldyn->volume;
+
+       return p;
+}
+
 double pressure_calc(t_moldyn *moldyn) {
 
        int i;
-       t_atom *atom;
-       double p1,p2,p=0;
-       
+       double v;
+       t_virial *virial;
+
+       /*
+        * P = 1/(3V) sum_i ( p_i^2 / 2m + f_i r_i )
+        *
+        * virial = f_i r_i
+        */
+
+       v=0.0;
        for(i=0;i<moldyn->count;i++) {
-               
+               virial=&(moldyn->atom[i].virial);
+               v+=(virial->xx+virial->yy+virial->zz);
+       }
+
+       /* assume up to date kinetic energy */
+       moldyn->p=2.0*moldyn->ekin+v;
+       moldyn->p/=(3.0*moldyn->volume);
 
+       return moldyn->p;
+}      
+
+double thermodynamic_pressure_calc(t_moldyn *moldyn) {
+
+       t_3dvec dim,*tp;
+       double u,p;
+       double scale;
+       t_atom *store;
+
+       tp=&(moldyn->tp);
+       store=malloc(moldyn->count*sizeof(t_atom));
+       if(store==NULL) {
+               printf("[moldyn] allocating store mem failed\n");
+               return -1;
        }
 
-       p1=(moldyn->count*K_BOLTZMANN*moldyn->t-ONE_THIRD*moldyn->vt1);
-       p1/=moldyn->volume;
+       /* save unscaled potential energy + atom/dim configuration */
+       u=moldyn->energy;
+       memcpy(store,moldyn->atom,moldyn->count*sizeof(t_atom));
+       dim=moldyn->dim;
 
-       p2=(moldyn->count*K_BOLTZMANN*moldyn->t-ONE_THIRD*moldyn->vt2);
-       p2/=moldyn->volume;
+       /* derivative with respect to x direction */
+       scale=1.0+moldyn->dv/(moldyn->dim.y*moldyn->dim.z);
+       scale_dim(moldyn,scale,TRUE,0,0);
+       scale_atoms(moldyn,scale,TRUE,0,0);
+       link_cell_shutdown(moldyn);
+       link_cell_init(moldyn);
+       potential_force_calc(moldyn);
+       tp->x=(moldyn->energy-u)/moldyn->dv;
+       p=tp->x*tp->x;
 
-       printf("compare pressures: %f %f\n",p1/ATM,p2/ATM);
+       /* restore atomic configuration + dim */
+       memcpy(moldyn->atom,store,moldyn->count*sizeof(t_atom));
+       moldyn->dim=dim;
 
-       return moldyn->p;
-}      
+       /* derivative with respect to y direction */
+       scale=1.0+moldyn->dv/(moldyn->dim.x*moldyn->dim.z);
+       scale_dim(moldyn,scale,0,TRUE,0);
+       scale_atoms(moldyn,scale,0,TRUE,0);
+       link_cell_shutdown(moldyn);
+       link_cell_init(moldyn);
+       potential_force_calc(moldyn);
+       tp->y=(moldyn->energy-u)/moldyn->dv;
+       p+=tp->y*tp->y;
+
+       /* restore atomic configuration + dim */
+       memcpy(moldyn->atom,store,moldyn->count*sizeof(t_atom));
+       moldyn->dim=dim;
+
+       /* derivative with respect to z direction */
+       scale=1.0+moldyn->dv/(moldyn->dim.x*moldyn->dim.y);
+       scale_dim(moldyn,scale,0,0,TRUE);
+       scale_atoms(moldyn,scale,0,0,TRUE);
+       link_cell_shutdown(moldyn);
+       link_cell_init(moldyn);
+       potential_force_calc(moldyn);
+       tp->z=(moldyn->energy-u)/moldyn->dv;
+       p+=tp->z*tp->z;
+
+       /* restore atomic configuration + dim */
+       memcpy(moldyn->atom,store,moldyn->count*sizeof(t_atom));
+       moldyn->dim=dim;
+
+       printf("dU/dV komp addiert = %f %f %f\n",tp->x,tp->y,tp->z);
+
+       scale=1.0+pow(moldyn->dv/moldyn->volume,ONE_THIRD);
+
+printf("debug: %f %f\n",moldyn->atom[0].r.x,moldyn->dim.x);
+       scale_dim(moldyn,scale,1,1,1);
+       scale_atoms(moldyn,scale,1,1,1);
+       link_cell_shutdown(moldyn);
+       link_cell_init(moldyn);
+       potential_force_calc(moldyn);
+printf("debug: %f %f\n",moldyn->atom[0].r.x,moldyn->dim.x);
+
+       printf("dU/dV einfach = %f\n",((moldyn->energy-u)/moldyn->dv)/ATM);
+
+       /* restore atomic configuration + dim */
+       memcpy(moldyn->atom,store,moldyn->count*sizeof(t_atom));
+       moldyn->dim=dim;
+
+       /* restore energy */
+       moldyn->energy=u;
+
+       link_cell_shutdown(moldyn);
+       link_cell_init(moldyn);
+
+       return sqrt(p);
+}
 
 double get_pressure(t_moldyn *moldyn) {
 
@@ -566,6 +790,34 @@ double get_pressure(t_moldyn *moldyn) {
 
 }
 
+int scale_dim(t_moldyn *moldyn,double scale,u8 x,u8 y,u8 z) {
+
+       t_3dvec *dim;
+
+       dim=&(moldyn->dim);
+
+       if(x) dim->x*=scale;
+       if(y) dim->y*=scale;
+       if(z) dim->z*=scale;
+
+       return 0;
+}
+
+int scale_atoms(t_moldyn *moldyn,double scale,u8 x,u8 y,u8 z) {
+
+       int i;
+       t_3dvec *r;
+
+       for(i=0;i<moldyn->count;i++) {
+               r=&(moldyn->atom[i].r);
+               if(x) r->x*=scale;
+               if(y) r->y*=scale;
+               if(z) r->z*=scale;
+       }
+
+       return 0;
+}
+
 int scale_volume(t_moldyn *moldyn) {
 
        t_atom *atom;
@@ -846,10 +1098,14 @@ int moldyn_add_schedule(t_moldyn *moldyn,int runs,double tau) {
        schedule->tau=ptr;
        schedule->tau[count-1]=tau;
 
+       printf("[moldyn] schedule added:\n");
+       printf("  number: %d | runs: %d | tau: %f\n",count-1,runs,tau);
+                                      
+
        return 0;
 }
 
-int moldyn_set_schedule_hook(t_moldyn *moldyn,void *hook,void *hook_params) {
+int moldyn_set_schedule_hook(t_moldyn *moldyn,set_hook hook,void *hook_params) {
 
        moldyn->schedule.hook=hook;
        moldyn->schedule.hook_params=hook_params;
@@ -875,6 +1131,7 @@ int moldyn_integrate(t_moldyn *moldyn) {
        int fd;
        char dir[128];
        double ds;
+       double energy_scale;
 
        sched=&(moldyn->schedule);
        atom=moldyn->atom;
@@ -892,8 +1149,13 @@ int moldyn_integrate(t_moldyn *moldyn) {
        moldyn->tau_square=moldyn->tau*moldyn->tau;
        moldyn->cutoff_square=moldyn->cutoff*moldyn->cutoff;
 
+       /* energy scaling factor */
+       energy_scale=moldyn->count*EV;
+
+printf("debug: %f\n",moldyn->atom[0].f.x);
        /* calculate initial forces */
        potential_force_calc(moldyn);
+printf("debug: %f\n",moldyn->atom[0].f.x);
 
        /* some stupid checks before we actually start calculating bullshit */
        if(moldyn->cutoff>0.5*moldyn->dim.x)
@@ -912,6 +1174,9 @@ int moldyn_integrate(t_moldyn *moldyn) {
        /* debugging, ignore */
        moldyn->debug=0;
 
+       /* tell the world */
+       printf("[moldyn] integration start, go get a coffee ...\n");
+
        /* executing the schedule */
        for(sched->count=0;sched->count<sched->total_sched;sched->count++) {
 
@@ -933,22 +1198,19 @@ int moldyn_integrate(t_moldyn *moldyn) {
                if(moldyn->pt_scale&(P_SCALE_BERENDSEN|P_SCALE_DIRECT))
                        scale_volume(moldyn);
 
+               update_e_kin(moldyn);
+               temperature_calc(moldyn);
+               pressure_calc(moldyn);
+               //thermodynamic_pressure_calc(moldyn);
+
                /* check for log & visualization */
-//double ax;
-//double ao;
-//double av;
                if(e) {
                        if(!(i%e))
-//ao=sqrt(0.1/M_SI);
-//ax=((0.28-0.25)*sqrt(3)*LC_SI/2)*cos(ao*i);
-//av=ao*(0.28-0.25)*sqrt(3)*LC_SI/2*sin(ao*i);
-                               update_e_kin(moldyn);
                                dprintf(moldyn->efd,
                                        "%f %f %f %f\n",
-                                       moldyn->time,moldyn->ekin,
-                                       moldyn->energy,
-                                       get_total_energy(moldyn));
-//moldyn->atom[0].r.x,ax,av*av*M_SI,0.1*ax*ax,av*av*M_SI+0.1*ax*ax);
+                                       moldyn->time,moldyn->ekin/energy_scale,
+                                       moldyn->energy/energy_scale,
+                                       get_total_energy(moldyn)/energy_scale);
                }
                if(m) {
                        if(!(i%m)) {
@@ -975,8 +1237,8 @@ int moldyn_integrate(t_moldyn *moldyn) {
                        if(!(i%v)) {
                                visual_atoms(&(moldyn->vis),moldyn->time,
                                             moldyn->atom,moldyn->count);
-                               printf("\rsched: %d, steps: %d, debug: %d",
-                                      sched->count,i,moldyn->debug);
+                               printf("\rsched: %d, steps: %d, debug: %f",
+                                      sched->count,i,moldyn->p/ATM);
                                fflush(stdout);
                        }
                }
@@ -1069,27 +1331,29 @@ int potential_force_calc(t_moldyn *moldyn) {
        /* reset energy */
        moldyn->energy=0.0;
 
-       moldyn->vt2=0.0;
-       
-       /* get energy and force of every atom */
+       /* reset force, site energy and virial of every atom */
        for(i=0;i<count;i++) {
 
                /* reset force */
                v3_zero(&(itom[i].f));
 
-               /* reset viral of atom i */
-               virial=&(itom[i].virial);
+               /* reset virial */
+               virial=(&(itom[i].virial));
                virial->xx=0.0;
                virial->yy=0.0;
                virial->zz=0.0;
                virial->xy=0.0;
                virial->xz=0.0;
                virial->yz=0.0;
-               moldyn->vt1=0.0;
-
+       
                /* reset site energy */
                itom[i].e=0.0;
 
+       }
+
+       /* get energy,force and virial of every atom */
+       for(i=0;i<count;i++) {
+
                /* single particle potential/force */
                if(itom[i].attr&ATOM_ATTR_1BP)
                        moldyn->func1b(moldyn,&(itom[i]));
@@ -1188,6 +1452,7 @@ int potential_force_calc(t_moldyn *moldyn) {
                }
 
        }
+
 #ifdef DEBUG
 printf("\n\n");
 #endif
@@ -1195,14 +1460,6 @@ printf("\n\n");
 printf("\n\n");
 #endif
 
-       moldyn->vt2=0.0;
-       for(i=0;i<count;i++)
-               moldyn->vt2-=v3_scalar_product(&(itom[i].r),&(itom[i].f));
-
-printf("compare: vt1: %f vt2: %f\n",moldyn->vt1,moldyn->vt2);
-
-pressure_calc(moldyn);
-
        return 0;
 }
 
@@ -1212,12 +1469,12 @@ pressure_calc(moldyn);
 
 inline int virial_calc(t_atom *a,t_3dvec *f,t_3dvec *d) {
 
-       a->virial.xx-=f->x*d->x;
-       a->virial.yy-=f->y*d->y;
-       a->virial.zz-=f->z*d->z;
-       a->virial.xy-=f->x*d->y;
-       a->virial.xz-=f->x*d->z;
-       a->virial.yz-=f->y*d->z;
+       a->virial.xx+=f->x*d->x;
+       a->virial.yy+=f->y*d->y;
+       a->virial.zz+=f->z*d->z;
+       a->virial.xy+=f->x*d->y;
+       a->virial.xz+=f->x*d->z;
+       a->virial.yz+=f->y*d->z;
 
        return 0;
 }
@@ -1325,11 +1582,10 @@ int lennard_jones(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
                d*=eps;
                v3_scale(&force,&distance,d);
                v3_add(&(aj->f),&(aj->f),&force);
-               v3_scale(&force,&distance,-1.0*d); /* f = - grad E */
+               v3_scale(&force,&force,-1.0); /* f = - grad E */
                v3_add(&(ai->f),&(ai->f),&force);
                virial_calc(ai,&force,&distance);
                virial_calc(aj,&force,&distance); /* f and d signe switched */
-               moldyn->vt1-=v3_scalar_product(&force,&distance);
        }
 
        return 0;