+/* 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 (m) | %.12f | %.12f | %.12f\n",p->S[0],p->S[1],p->Smixed);
+ printf(" R (m) | %.12f | %.12f | %.12f\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=&(params->beta[num]);
+ exchange->n=&(params->n[num]);
+ exchange->c=&(params->c[num]);
+ exchange->d=&(params->d[num]);
+ exchange->h=&(params->h[num]);
+
+ exchange->betan=pow(*(exchange->beta),*(exchange->n));
+ exchange->n_betan=*(exchange->n)*exchange->betan;
+ exchange->c2=params->c[num]*params->c[num];
+ exchange->d2=params->d[num]*params->d[num];
+ exchange->c2d2=exchange->c2/exchange->d2;
+
+ 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;
+ double scale;
+
+ params=moldyn->pot2b_params;
+ num=ai->bnum;
+ exchange=&(params->exchange);
+
+ exchange->run3bp=0;
+
+ /*
+ * we need: f_c, df_c, f_r, df_r
+ *
+ * therefore we need: R, S, A, lambda
+ */
+
+ v3_sub(&dist_ij,&(ai->r),&(aj->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;
+ exchange->d_ij2=d_ij*d_ij;
+
+ /* constants */
+ if(num==aj->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];
+ params->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)
+ return 0;
+
+ f_r=A*exp(-lambda*d_ij);
+ df_r=-lambda*f_r/d_ij;
+
+ /* f_a, df_a calc + save for 3bp use */
+ exchange->f_a=-B*exp(-mu*d_ij);
+ exchange->df_a=-mu*exchange->f_a/d_ij;
+
+ if(d_ij<R) {
+ /* f_c = 1, df_c = 0 */
+ f_c=1.0;
+ df_c=0.0;
+ v3_scale(&force,&dist_ij,df_r);
+ }
+ else {
+ s_r=S-R;
+ arg=M_PI*(d_ij-R)/s_r;
+ f_c=0.5+0.5*cos(arg);
+ df_c=-0.5*sin(arg)*(M_PI/(s_r*d_ij));
+ scale=df_c*f_r+df_r*f_c;
+ v3_scale(&force,&dist_ij,scale);
+ }
+
+ /* add forces */
+ v3_add(&(ai->f),&(ai->f),&force);
+ /* energy is 0.5 f_r f_c ... */
+ moldyn->energy+=(0.5*f_r*f_c);
+
+ /* save for use in 3bp */
+ exchange->f_c=f_c;
+ exchange->df_c=df_c;
+
+ /* enable the run of 3bp function */
+ exchange->run3bp=1;
+
+ /* reset 3bp sums */
+ exchange->sum1_3bp=0.0;
+ exchange->sum2_3bp=0.0;
+ v3_zero(&(exchange->db_ij));
+
+ return 0;
+}
+
+/* tersoff 2 body post part */
+
+int tersoff_mult_post_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
+
+ /* here we have to allow for the 3bp sums */
+
+ t_tersoff_mult_params *params;
+ t_tersoff_exchange *exchange;
+
+ t_3dvec force,temp,*db_ij,*dist_ij;
+ double db_ij_scale1,db_ij_scale2;
+ double b_ij;
+ double f_c,df_c,f_a,df_a;
+ double chi,betan;
+ double help;
+ double n;
+
+ params=moldyn->pot2b_params;
+ exchange=&(params->exchange);
+
+ db_ij=&(exchange->db_ij);
+ f_c=exchange->f_c;
+ df_c=exchange->df_c;
+ f_a=exchange->f_a;
+ df_a=exchange->df_a;
+ betan=exchange->betan;
+ n=*(exchange->n);
+ dist_ij=&(exchange->dist_ij);
+
+ db_ij_scale1=(1+betan*exchange->sum1_3bp);
+ db_ij_scale2=(exchange->n_betan*exchange->sum2_3bp);
+ help=pow(db_ij_scale1,-1.0/(2*n)-1);
+ b_ij=chi*db_ij_scale1*help;
+ db_ij_scale1=-chi/(2*n)*help;
+
+ v3_scale(db_ij,db_ij,(db_ij_scale1*db_ij_scale2));
+ v3_scale(db_ij,db_ij,f_a);
+
+ v3_scale(&temp,dist_ij,b_ij*df_a);
+
+ v3_add(&force,&temp,db_ij);
+ v3_scale(&force,&force,f_c);
+
+ v3_scale(&temp,dist_ij,f_a*b_ij*df_c);
+
+ /* add energy of 3bp sum */
+ moldyn->energy+=(0.5*f_c*b_ij*f_a);
+ /* add force of 3bp calculation */
+ v3_add(&(ai->f),&temp,&force);
+
+ return 0;
+}
+
+/* tersoff 3 body part */
+
+int tersoff_mult_3bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,t_atom *ak,u8 bc) {
+
+ t_tersoff_mult_params *params;
+ t_tersoff_exchange *exchange;
+ t_3dvec dist_ij,dist_ik,dist_jk;
+ t_3dvec temp,force;
+ double R,S,s_r;
+ double d_ij,d_ij2,d_ik,d_jk;
+ double f_c,df_c,f_a,df_a;
+ double f_c_ik,df_c_ik,arg;
+ double n,c,d,h;
+ double c2,d2,c2d2;
+ double numer,denom;
+ double theta,cos_theta,sin_theta;
+ double d_theta,d_theta1,d_theta2;
+ double h_cos,d2_h_cos2;
+ double frac,bracket,bracket_n_1,bracket_n;
+ double g;
+ int num;
+
+ params=moldyn->pot3b_params;
+ num=ai->bnum;
+ exchange=&(params->exchange);
+
+ if(!(exchange->run3bp))
+ return 0;
+
+ /*
+ * we need: f_c, d_fc, b_ij, db_ij, f_a, df_a
+ *
+ * we got f_c, df_c, f_a, df_a from 2bp calculation
+ */
+
+ d_ij=exchange->d_ij;
+ d_ij2=exchange->d_ij2;
+ dist_ij=exchange->dist_ij;
+
+ f_a=params->exchange.f_a;
+ df_a=params->exchange.df_a;
+
+ f_c=exchange->f_c;
+ df_c=exchange->df_c;
+
+ /* d_ij is <= S, as we didn't return so far! */
+
+ /*
+ * calc of b_ij (scalar) and db_ij (vector)
+ *
+ * - for b_ij: chi, beta, f_c_ik, w(=1), c, d, h, n, cos_theta
+ *
+ * - for db_ij: d_theta, sin_theta, cos_theta, f_c_ik, df_c_ik,
+ * w_ik,
+ *
+ */
+
+ v3_sub(&dist_ik,&(ai->r),&(ak->r));
+ if(bc) check_per_bound(moldyn,&dist_ik);
+ d_ik=v3_norm(&dist_ik);
+
+ /* constants for f_c_ik calc */
+ if(num==ak->bnum) {
+ R=params->R[num];
+ S=params->S[num];
+ }
+ else {
+ R=params->Rmixed;
+ S=params->Smixed;