+ /* f_c_ij, df_c_ij (same for ji) */
+ f_c=exchange->f_c;
+ df_c=exchange->df_c;
+
+ /*
+ * calculate unknown values now ...
+ */
+
+ /* V_ij and dV_ij stuff (in b_ij there is f_c_ik) */
+
+ /* dist_ik, d_ik */
+ v3_sub(&dist_ik,&(ak->r),&(ai->r));
+ if(bc) check_per_bound(moldyn,&dist_ik);
+ d_ik=v3_norm(&dist_ik);
+
+ /* ik constants */
+ num=ai->bnum;
+ if(num==ak->bnum) {
+ R=params->R[num];
+ S=params->S[num];
+ }
+ else {
+ R=params->Rmixed;
+ S=params->Smixed;
+ }
+
+ /* zeta_ij/dzeta_ij contribution only for d_ik < S */
+ if(d_ik<S) {
+
+ /* get constants_i from exchange data */
+ n=*(exchange->n_i);
+ c=*(exchange->c_i);
+ d=*(exchange->d_i);
+ h=*(exchange->h_i);
+ c2=exchange->ci2;
+ d2=exchange->di2;
+ c2d2=exchange->ci2di2;
+
+ /* cosine of theta_ijk by scalaproduct */
+ rr=v3_scalar_product(&dist_ij,&dist_ik);
+ dd=d_ij*d_ik;
+ cos_theta=rr/dd;
+
+ /* d_costheta */
+ tmp=1.0/dd;
+ d_costheta1=cos_theta/(d_ij*d_ij)-tmp;
+ d_costheta2=cos_theta/(d_ik*d_ik)-tmp;
+
+ /* some usefull values */
+ h_cos=(h-cos_theta);
+ d2_h_cos2=d2+(h_cos*h_cos);
+ frac=c2/(d2_h_cos2);
+
+ /* g(cos_theta) */
+ g=1.0+c2d2-frac;
+
+ /* d_costheta_ij and dg(cos_theta) - needed in any case! */
+ v3_scale(&temp1,&dist_ij,d_costheta1);
+ v3_scale(&temp2,&dist_ik,d_costheta2);
+ v3_add(&temp1,&temp1,&temp2);
+ v3_scale(&temp1,&temp1,-2.0*frac*h_cos/d2_h_cos2); /* dg */
+
+ /* f_c_ik & df_c_ik + {d,}zeta contribution */
+ dzeta=&(exchange->dzeta_ij);
+ if(d_ik<R) {
+ /* {d,}f_c_ik */
+ // => f_c_ik=1.0;
+ // => df_c_ik=0.0; of course we do not set this!
+
+ /* zeta_ij */
+ exchange->zeta_ij+=g;
+
+ /* dzeta_ij */
+ v3_add(dzeta,dzeta,&temp1);
+ }
+ else {
+ /* {d,}f_c_ik */
+ s_r=S-R;
+ arg=M_PI*(d_ik-R)/s_r;
+ f_c_ik=0.5+0.5*cos(arg);
+ //df_c_ik=-0.5*sin(arg)*(M_PI/(s_r*d_ik)); /* MARK */
+ df_c_ik=0.5*sin(arg)*(M_PI/(s_r*d_ik));
+
+ /* zeta_ij */
+ exchange->zeta_ij+=f_c_ik*g;
+
+ /* dzeta_ij */
+ v3_scale(&temp1,&temp1,f_c_ik);
+ v3_scale(&temp2,&dist_ik,g*df_c_ik);
+ v3_add(&temp1,&temp1,&temp2);
+ v3_add(dzeta,dzeta,&temp1);
+ }
+ }
+
+ /* dV_ji stuff (in b_ji there is f_c_jk) + dV_jk stuff! */
+
+ /* dist_jk, d_jk */
+ v3_sub(&dist_jk,&(ak->r),&(aj->r));
+ if(bc) check_per_bound(moldyn,&dist_jk);
+ d_jk=v3_norm(&dist_jk);
+
+ /* jk constants */
+ num=aj->bnum;
+ if(num==ak->bnum) {
+ R=params->R[num];
+ S=params->S[num];
+ B=params->B[num];
+ mu=params->mu[num];
+ chi=1.0;
+ }
+ else {
+ R=params->Rmixed;
+ S=params->Smixed;
+ B=params->Bmixed;
+ mu=params->mu_m;
+ chi=params->chi;
+ }
+
+ /* zeta_ji/dzeta_ji contribution only for d_jk < S_jk */
+ if(d_jk<S) {
+
+ /* constants_j from exchange data */
+ n=*(exchange->n_j);
+ c=*(exchange->c_j);
+ d=*(exchange->d_j);
+ h=*(exchange->h_j);
+ c2=exchange->cj2;
+ d2=exchange->dj2;
+ c2d2=exchange->cj2dj2;
+
+ /* cosine of theta_jik by scalaproduct */
+ rr=-v3_scalar_product(&dist_ij,&dist_jk); /* -1, as ij -> ji */
+ dd=d_ij*d_jk;
+ cos_theta=rr/dd;
+
+ /* d_costheta */
+ d_costheta1=1.0/dd;
+ d_costheta2=cos_theta/(d_ij*d_ij);
+
+ /* some usefull values */
+ h_cos=(h-cos_theta);
+ d2_h_cos2=d2+(h_cos*h_cos);
+ frac=c2/(d2_h_cos2);
+
+ /* g(cos_theta) */
+ g=1.0+c2d2-frac;
+
+ /* d_costheta_ij and dg(cos_theta) - needed in any case! */
+ v3_scale(&temp1,&dist_jk,d_costheta1);
+ v3_scale(&temp2,&dist_ij,-d_costheta2); /* ji -> ij => -1 */
+ v3_add(&temp1,&temp1,&temp2);
+ v3_scale(&temp1,&temp1,-2.0*frac*h_cos/d2_h_cos2); /* dg */
+
+ /* store dg in temp2 and use it for dVjk later */
+ v3_copy(&temp2,&temp1);
+
+ /* f_c_jk + {d,}zeta contribution (df_c_jk = 0) */
+ dzeta=&(exchange->dzeta_ji);
+ if(d_jk<R) {
+ /* f_c_jk */
+ f_c_jk=1.0;
+
+ /* zeta_ji */
+ exchange->zeta_ji+=g;
+
+ /* dzeta_ji */
+ v3_add(dzeta,dzeta,&temp1);
+ }
+ else {
+ /* f_c_jk */
+ s_r=S-R;
+ arg=M_PI*(d_jk-R)/s_r;
+ f_c_jk=0.5+0.5*cos(arg);
+
+ /* zeta_ji */
+ exchange->zeta_ji+=f_c_jk*g;
+
+ /* dzeta_ji */
+ v3_scale(&temp1,&temp1,f_c_jk);
+ v3_add(dzeta,dzeta,&temp1);
+ }
+
+ /* dV_jk stuff | add force contribution on atom i immediately */
+ if(exchange->d_ij_between_rs) {
+ zeta=f_c*g;
+ v3_scale(&temp1,&temp2,f_c);
+ v3_scale(&temp2,&dist_ij,df_c*g);
+ v3_add(&temp2,&temp2,&temp1); /* -> dzeta_jk in temp2 */
+ }
+ else {
+ zeta=g;
+ // dzeta_jk is simply dg, which is stored in temp2
+ }
+ /* betajnj * zeta_jk ^ nj-1 */
+ tmp=exchange->betajnj*pow(zeta,(n-1.0));
+ tmp=-chi/2.0*pow((1+tmp*zeta),(-1.0/(2.0*n)-1))*tmp;
+ v3_scale(&temp2,&temp2,tmp*B*exp(-mu*d_jk)*f_c_jk*0.5);
+ v3_add(&(ai->f),&(ai->f),&temp2); /* -1 skipped in f_a calc ^ */
+ /* scaled with 0.5 ^ */
+
+ }
+
+ return 0;
+}
+
+
+/*
+ * debugging / critical check functions
+ */
+
+int moldyn_bc_check(t_moldyn *moldyn) {
+
+ t_atom *atom;
+ t_3dvec *dim;
+ int i;
+double x;
+u8 byte;
+int j,k;
+
+ atom=moldyn->atom;
+ dim=&(moldyn->dim);
+x=dim->x/2;
+
+ for(i=0;i<moldyn->count;i++) {
+ if(atom[i].r.x>=dim->x/2||-atom[i].r.x>dim->x/2) {
+ printf("FATAL: atom %d: x: %.20f (%.20f)\n",
+ i,atom[i].r.x,dim->x/2);
+ printf("diagnostic:\n");
+ printf("-----------\natom.r.x:\n");
+ for(j=0;j<8;j++) {
+ memcpy(&byte,(u8 *)(&(atom[i].r.x))+j,1);
+ for(k=0;k<8;k++)
+ printf("%d%c",
+ ((byte)&(1<<k))?1:0,
+ (k==7)?'\n':'|');
+ }
+ printf("---------------\nx=dim.x/2:\n");
+ for(j=0;j<8;j++) {
+ memcpy(&byte,(u8 *)(&x)+j,1);
+ for(k=0;k<8;k++)
+ printf("%d%c",
+ ((byte)&(1<<k))?1:0,
+ (k==7)?'\n':'|');