+ /* virial sum and mean virial */
+ moldyn->virial_sum+=v;
+ moldyn->mean_v=moldyn->virial_sum/moldyn->total_steps;
+
+ /* assume up to date kinetic energy */
+ moldyn->p=2.0*moldyn->ekin+moldyn->mean_v;
+ moldyn->p/=(3.0*moldyn->volume);
+ moldyn->p_sum+=moldyn->p;
+ moldyn->mean_p=moldyn->p_sum/moldyn->total_steps;
+
+ /* pressure from 'absolute coordinates' virial */
+ virial=&(moldyn->virial);
+ v=virial->xx+virial->yy+virial->zz;
+ moldyn->gp=2.0*moldyn->ekin+v;
+ moldyn->gp/=(3.0*moldyn->volume);
+ moldyn->gp_sum+=moldyn->gp;
+ moldyn->mean_gp=moldyn->gp_sum/moldyn->total_steps;
+
+ return moldyn->p;
+}
+
+double thermodynamic_pressure_calc(t_moldyn *moldyn) {
+
+ t_3dvec dim,*tp;
+ double u_up,u_down,dv;
+ double scale,p;
+ t_atom *store;
+
+ /*
+ * dU = - p dV
+ *
+ * => p = - dU/dV
+ *
+ */
+
+ scale=0.00001;
+ dv=8*scale*scale*scale*moldyn->volume;
+
+ store=malloc(moldyn->count*sizeof(t_atom));
+ if(store==NULL) {
+ printf("[moldyn] allocating store mem failed\n");
+ return -1;
+ }
+
+ /* save unscaled potential energy + atom/dim configuration */
+ memcpy(store,moldyn->atom,moldyn->count*sizeof(t_atom));
+ dim=moldyn->dim;
+
+ /* scale up dimension and atom positions */
+ scale_dim(moldyn,SCALE_UP,scale,TRUE,TRUE,TRUE);
+ scale_atoms(moldyn,SCALE_UP,scale,TRUE,TRUE,TRUE);
+ link_cell_shutdown(moldyn);
+ link_cell_init(moldyn,QUIET);
+ potential_force_calc(moldyn);
+ u_up=moldyn->energy;
+
+ /* restore atomic configuration + dim */
+ memcpy(moldyn->atom,store,moldyn->count*sizeof(t_atom));
+ moldyn->dim=dim;
+
+ /* scale down dimension and atom positions */
+ scale_dim(moldyn,SCALE_DOWN,scale,TRUE,TRUE,TRUE);
+ scale_atoms(moldyn,SCALE_DOWN,scale,TRUE,TRUE,TRUE);
+ link_cell_shutdown(moldyn);
+ link_cell_init(moldyn,QUIET);
+ potential_force_calc(moldyn);
+ u_down=moldyn->energy;
+
+ /* calculate pressure */
+ p=-(u_up-u_down)/dv;
+printf("-------> %.10f %.10f %f\n",u_up/EV/moldyn->count,u_down/EV/moldyn->count,p/BAR);
+
+ /* restore atomic configuration + dim */
+ memcpy(moldyn->atom,store,moldyn->count*sizeof(t_atom));
+ moldyn->dim=dim;
+
+ /* restore energy */
+ potential_force_calc(moldyn);
+
+ link_cell_shutdown(moldyn);
+ link_cell_init(moldyn,QUIET);
+
+ return p;
+}
+
+double get_pressure(t_moldyn *moldyn) {
+
+ return moldyn->p;
+
+}
+
+int scale_dim(t_moldyn *moldyn,u8 dir,double scale,u8 x,u8 y,u8 z) {
+
+ t_3dvec *dim;
+
+ dim=&(moldyn->dim);
+
+ if(dir==SCALE_UP)
+ scale=1.0+scale;
+
+ if(dir==SCALE_DOWN)
+ scale=1.0-scale;
+
+ if(x) dim->x*=scale;
+ if(y) dim->y*=scale;
+ if(z) dim->z*=scale;
+
+ return 0;
+}
+
+int scale_atoms(t_moldyn *moldyn,u8 dir,double scale,u8 x,u8 y,u8 z) {
+
+ int i;
+ t_3dvec *r;
+
+ if(dir==SCALE_UP)
+ scale=1.0+scale;
+
+ if(dir==SCALE_DOWN)
+ scale=1.0-scale;
+
+ 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;