+ v3_sub(&distance,&(aj->r),&(ai->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,-1.0*d); /* f = - grad E */
+ v3_add(&(ai->f),&(ai->f),&force);
+ }
+
+ return 0;
+}
+
+/*
+ * tersoff potential & force for 2 sorts of atoms
+ */
+
+/* create mixed terms from parameters and set them */
+int tersoff_mult_complete_params(t_tersoff_mult_params *p) {
+
+ printf("[moldyn] tersoff parameter completion\n");
+ p->Smixed=sqrt(p->S[0]*p->S[1]);
+ p->Rmixed=sqrt(p->R[0]*p->R[1]);
+ p->Amixed=sqrt(p->A[0]*p->A[1]);
+ p->Bmixed=sqrt(p->B[0]*p->B[1]);
+ p->lambda_m=0.5*(p->lambda[0]+p->lambda[1]);
+ p->mu_m=0.5*(p->mu[0]+p->mu[1]);
+
+ printf("[moldyn] tersoff mult parameter info:\n");
+ printf(" S (A) | %f | %f | %f\n",p->S[0],p->S[1],p->Smixed);
+ printf(" R (A) | %f | %f | %f\n",p->R[0],p->R[1],p->Rmixed);
+ printf(" A (eV) | %f | %f | %f\n",p->A[0]/EV,p->A[1]/EV,p->Amixed/EV);
+ printf(" B (eV) | %f | %f | %f\n",p->B[0]/EV,p->B[1]/EV,p->Bmixed/EV);
+ printf(" lambda | %f | %f | %f\n",p->lambda[0],p->lambda[1],
+ p->lambda_m);
+ printf(" mu | %f | %f | %f\n",p->mu[0],p->mu[1],p->mu_m);
+ printf(" beta | %.10f | %.10f\n",p->beta[0],p->beta[1]);
+ printf(" n | %f | %f\n",p->n[0],p->n[1]);
+ printf(" c | %f | %f\n",p->c[0],p->c[1]);
+ printf(" d | %f | %f\n",p->d[0],p->d[1]);
+ printf(" h | %f | %f\n",p->h[0],p->h[1]);
+ printf(" chi | %f \n",p->chi);
+
+ return 0;
+}
+
+/* tersoff 1 body part */
+int tersoff_mult_1bp(t_moldyn *moldyn,t_atom *ai) {
+
+ int num;
+ t_tersoff_mult_params *params;
+ t_tersoff_exchange *exchange;
+
+ num=ai->bnum;
+ params=moldyn->pot1b_params;
+ exchange=&(params->exchange);
+
+ /*
+ * simple: point constant parameters only depending on atom i to
+ * their right values
+ */
+
+ exchange->beta_i=&(params->beta[num]);
+ exchange->n_i=&(params->n[num]);
+ exchange->c_i=&(params->c[num]);
+ exchange->d_i=&(params->d[num]);
+ exchange->h_i=&(params->h[num]);
+
+ exchange->betaini=pow(*(exchange->beta_i),*(exchange->n_i));
+ exchange->ci2=params->c[num]*params->c[num];
+ exchange->di2=params->d[num]*params->d[num];
+ exchange->ci2di2=exchange->ci2/exchange->di2;
+
+ return 0;
+}
+
+/* tersoff 2 body part */
+int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
+
+ t_tersoff_mult_params *params;
+ t_tersoff_exchange *exchange;
+ t_3dvec dist_ij,force;
+ double d_ij;
+ double A,B,R,S,lambda,mu;
+ double f_r,df_r;
+ double f_c,df_c;
+ int num;
+ double s_r;
+ double arg;
+
+ params=moldyn->pot2b_params;
+ num=aj->bnum;
+ exchange=&(params->exchange);
+
+ /* clear 3bp and 2bp post run */
+ exchange->run3bp=0;
+ exchange->run2bp_post=0;
+
+ /* reset S > r > R mark */
+ exchange->d_ij_between_rs=0;
+
+ /*
+ * calc of 2bp contribution of V_ij and dV_ij/ji
+ *
+ * for Vij and dV_ij we need:
+ * - f_c_ij, df_c_ij
+ * - f_r_ij, df_r_ij
+ *
+ * for dV_ji we need:
+ * - f_c_ji = f_c_ij, df_c_ji = df_c_ij
+ * - f_r_ji = f_r_ij; df_r_ji = df_r_ij
+ *
+ */
+
+ /* dist_ij, d_ij */
+ v3_sub(&dist_ij,&(aj->r),&(ai->r));
+ if(bc) check_per_bound(moldyn,&dist_ij);
+ d_ij=v3_norm(&dist_ij);
+
+ /* save for use in 3bp */
+ exchange->d_ij=d_ij;
+ exchange->dist_ij=dist_ij;
+
+ /* constants */
+ if(num==ai->bnum) {
+ S=params->S[num];
+ R=params->R[num];
+ A=params->A[num];
+ B=params->B[num];
+ lambda=params->lambda[num];
+ mu=params->mu[num];
+ exchange->chi=1.0;
+ }
+ else {
+ S=params->Smixed;
+ R=params->Rmixed;
+ A=params->Amixed;
+ B=params->Bmixed;
+ lambda=params->lambda_m;
+ mu=params->mu_m;
+ params->exchange.chi=params->chi;
+ }
+
+ /* if d_ij > S => no force & potential energy contribution */
+ if(d_ij>S)
+ return 0;
+
+ /* more constants */
+ exchange->beta_j=&(params->beta[num]);
+ exchange->n_j=&(params->n[num]);
+ exchange->c_j=&(params->c[num]);
+ exchange->d_j=&(params->d[num]);
+ exchange->h_j=&(params->h[num]);
+ if(num==ai->bnum) {
+ exchange->betajnj=exchange->betaini;
+ exchange->cj2=exchange->ci2;
+ exchange->dj2=exchange->di2;
+ exchange->cj2dj2=exchange->ci2di2;