+ if(ai<aj) return 0;
+
+ 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 */
+ moldyn->energy+=(eps*(sig12*h1-sig6*h2)-params->uc);
+ 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,d);
+ v3_add(&(aj->f),&(aj->f),&force);
+ 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 */
+ }
+
+ 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->S2[0]=p->S[0]*p->S[0];
+ p->S2[1]=p->S[1]*p->S[1];
+ p->Smixed=sqrt(p->S[0]*p->S[1]);
+ p->S2mixed=p->Smixed*p->Smixed;
+ 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 brand;
+ t_tersoff_mult_params *params;
+ t_tersoff_exchange *exchange;
+
+ brand=ai->brand;
+ 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[brand]);
+ exchange->n_i=&(params->n[brand]);
+ exchange->c_i=&(params->c[brand]);
+ exchange->d_i=&(params->d[brand]);
+ exchange->h_i=&(params->h[brand]);
+
+ exchange->betaini=pow(*(exchange->beta_i),*(exchange->n_i));
+ exchange->ci2=params->c[brand]*params->c[brand];
+ exchange->di2=params->d[brand]*params->d[brand];
+ 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,d_ij2;
+ double A,B,R,S,S2,lambda,mu;
+ double f_r,df_r;
+ double f_c,df_c;
+ int brand;
+ double s_r;
+ double arg;
+
+ params=moldyn->pot2b_params;
+ brand=aj->brand;
+ 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
+ *
+ */
+
+ /* constants */
+ if(brand==ai->brand) {
+ S=params->S[brand];
+ S2=params->S2[brand];
+ R=params->R[brand];
+ A=params->A[brand];
+ B=params->B[brand];
+ lambda=params->lambda[brand];
+ mu=params->mu[brand];
+ exchange->chi=1.0;
+ }
+ else {
+ S=params->Smixed;
+ S2=params->S2mixed;
+ R=params->Rmixed;
+ A=params->Amixed;
+ B=params->Bmixed;
+ lambda=params->lambda_m;
+ mu=params->mu_m;
+ params->exchange.chi=params->chi;
+ }
+
+ /* dist_ij, d_ij */
+ v3_sub(&dist_ij,&(aj->r),&(ai->r));
+ if(bc) check_per_bound(moldyn,&dist_ij);
+ d_ij2=v3_absolute_square(&dist_ij);
+
+ /* if d_ij2 > S2 => no force & potential energy contribution */
+ if(d_ij2>S2)
+ return 0;
+
+ /* now we will need the distance */
+ //d_ij=v3_norm(&dist_ij);
+ d_ij=sqrt(d_ij2);
+
+ /* save for use in 3bp */
+ exchange->d_ij=d_ij;
+ exchange->d_ij2=d_ij2;
+ exchange->dist_ij=dist_ij;
+
+ /* more constants */
+ exchange->beta_j=&(params->beta[brand]);
+ exchange->n_j=&(params->n[brand]);
+ exchange->c_j=&(params->c[brand]);
+ exchange->d_j=&(params->d[brand]);
+ exchange->h_j=&(params->h[brand]);
+ if(brand==ai->brand) {
+ exchange->betajnj=exchange->betaini;
+ exchange->cj2=exchange->ci2;
+ exchange->dj2=exchange->di2;
+ exchange->cj2dj2=exchange->ci2di2;
+ }
+ else {
+ exchange->betajnj=pow(*(exchange->beta_j),*(exchange->n_j));
+ exchange->cj2=params->c[brand]*params->c[brand];
+ exchange->dj2=params->d[brand]*params->d[brand];
+ exchange->cj2dj2=exchange->cj2/exchange->dj2;