+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;
+ 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;
+ }
+
+ /* save unscaled potential energy + atom/dim configuration */
+ u=moldyn->energy;
+ memcpy(store,moldyn->atom,moldyn->count*sizeof(t_atom));
+ dim=moldyn->dim;
+
+ /* 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;
+
+ /* restore atomic configuration + dim */
+ memcpy(moldyn->atom,store,moldyn->count*sizeof(t_atom));
+ moldyn->dim=dim;
+
+ /* 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) {
+
+ return moldyn->p;
+
+}
+
+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;
+ t_3dvec *dim,*vdim;
+ double scale,v;
+ t_virial virial;
+ t_linkcell *lc;
+ int i;
+
+ atom=moldyn->atom;
+ dim=&(moldyn->dim);
+ vdim=&(moldyn->vis.dim);
+ lc=&(moldyn->lc);
+
+ memset(&virial,0,sizeof(t_virial));
+
+ for(i=0;i<moldyn->count;i++) {
+ virial.xx+=atom[i].virial.xx;
+ virial.yy+=atom[i].virial.yy;
+ virial.zz+=atom[i].virial.zz;
+ virial.xy+=atom[i].virial.xy;
+ virial.xz+=atom[i].virial.xz;
+ virial.yz+=atom[i].virial.yz;
+ }
+
+ /* just a guess so far ... */
+ v=virial.xx+virial.yy+virial.zz;
+
+printf("%f\n",v);
+ /* get pressure from virial */
+ moldyn->p=moldyn->count*K_BOLTZMANN*moldyn->t+ONE_THIRD*v;
+ moldyn->p/=moldyn->volume;
+printf("%f | %f\n",moldyn->p/(ATM),moldyn->p_ref/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;
+
+}
+