X-Git-Url: https://hackdaworld.org/gitweb/?a=blobdiff_plain;f=potentials%2Ftersoff.c;h=4ca7141d4252c0aade8386eb4bb3319e1712f594;hb=8524173a28f2c22a539ef1b0910a1136d9cb254b;hp=972075de6ec6d9fe7e07a1317304b82fc05034bf;hpb=296a35b943e922173ce648ec76a4472e287af108;p=physik%2Fposic.git

diff --git a/potentials/tersoff.c b/potentials/tersoff.c
index 972075d..4ca7141 100644
--- a/potentials/tersoff.c
+++ b/potentials/tersoff.c
@@ -20,20 +20,95 @@
 #include "tersoff.h"
 
 /* create mixed terms from parameters and set them */
-int tersoff_mult_complete_params(t_tersoff_mult_params *p) {
+int tersoff_mult_set_params(t_moldyn *moldyn,int element1,int element2) {
 
-	printf("[moldyn] tersoff parameter completion\n");
+	t_tersoff_mult_params *p;
+
+	// set cutoff before parameters (actually only necessary for some pots)
+	if(moldyn->cutoff==0.0) {
+		printf("[tersoff] WARNING: no cutoff!\n");
+		return -1;
+	}
+
+	/* alloc mem for potential parameters */
+	 moldyn->pot_params=malloc(sizeof(t_tersoff_mult_params));
+	 if(moldyn->pot_params==NULL) {
+	 	perror("[tersoff] pot params alloc");
+		return -1;
+	}
+
+	/* these are now tersoff parameters */
+	p=moldyn->pot_params;
+
+	// only 1 combination by now :p
+	switch(element1) {
+		case SI:
+			/* type: silicon */
+			p->S[0]=TM_S_SI;
+			p->R[0]=TM_R_SI;
+			p->A[0]=TM_A_SI;
+			p->B[0]=TM_B_SI;
+			p->lambda[0]=TM_LAMBDA_SI;
+			p->mu[0]=TM_MU_SI;
+			p->beta[0]=TM_BETA_SI;
+			p->n[0]=TM_N_SI;
+			p->c[0]=TM_C_SI;
+			p->d[0]=TM_D_SI;
+			p->h[0]=TM_H_SI;
+			switch(element2) {
+				case C:
+					p->chi=TM_CHI_SIC;
+					break;
+				default:
+					printf("[tersoff] WARNING: element2\n");
+					return -1;
+			}
+			break;
+		default:
+			printf("[tersoff] WARNING: element1\n");
+			return -1;
+	}
+
+	switch(element2) {
+		case C:
+			/* type carbon */
+			p->S[1]=TM_S_C;
+			p->R[1]=TM_R_C;
+			p->A[1]=TM_A_C;
+			p->B[1]=TM_B_C;
+			p->lambda[1]=TM_LAMBDA_C;
+			p->mu[1]=TM_MU_C;
+			p->beta[1]=TM_BETA_C;
+			p->n[1]=TM_N_C;
+			p->c[1]=TM_C_C;
+			p->d[1]=TM_D_C;
+			p->h[1]=TM_H_C;
+			break;
+		default:
+			printf("[tersoff] WARNING: element2\n");
+			return -1;
+	}
+
+	printf("[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->S2mixed=p->S[0]*p->S[1];
+	p->Smixed=sqrt(p->S2mixed);
 	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");
+	p->betaini[0]=pow(p->beta[0],p->n[0]);
+	p->betaini[1]=pow(p->beta[1],p->n[1]);
+	p->ci2[0]=p->c[0]*p->c[0];
+	p->ci2[1]=p->c[1]*p->c[1];
+	p->di2[0]=p->d[0]*p->d[0];
+	p->di2[1]=p->d[1]*p->d[1];
+	p->ci2di2[0]=p->ci2[0]/p->di2[0];
+	p->ci2di2[1]=p->ci2[1]/p->di2[1];
+
+	printf("[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);
@@ -51,147 +126,70 @@ int tersoff_mult_complete_params(t_tersoff_mult_params *p) {
 	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->pot_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 A,R,S,S2,lambda;
 	double f_r,df_r;
 	double f_c,df_c;
 	int brand;
 	double s_r;
 	double arg;
+	double energy;
 
-	params=moldyn->pot_params;
-	brand=aj->brand;
-	exchange=&(params->exchange);
+	printf("WARNING! - tersoff_mult_2bp is obsolete.\n");
+	printf("WARNING! - repulsive part handled in 3bp/j2 routine.\n");
 
-	/* clear 3bp and 2bp post run */
-	exchange->run3bp=0;
-	exchange->run2bp_post=0;
+	/* use newtons third law */
+	if(ai<aj) return 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
-	 *
-	 */
+	params=moldyn->pot_params;
+	brand=aj->brand;
 
-	/* constants */
-	if(brand==ai->brand) {
-		S=params->S[brand];
+	/* determine cutoff square */
+	if(brand==ai->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;
+	else
 		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 */
+	/* dist_ij, d_ij2 */
 	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)
+	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;
+		S=params->S[brand];
+		R=params->R[brand];
+		A=params->A[brand];
+		lambda=params->lambda[brand];
 	}
 	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;
+		S=params->Smixed;
+		R=params->Rmixed;
+		A=params->Amixed;
+		lambda=params->lambda_m;
 	}
 
-	/* f_r_ij = f_r_ji, df_r_ij = df_r_ji */
+	/* f_r_ij, df_r_ij */
 	f_r=A*exp(-lambda*d_ij);
 	df_r=lambda*f_r/d_ij;
 
-	/* f_a, df_a calc (again, same for ij and ji) | save for later use! */
-	exchange->f_a=-B*exp(-mu*d_ij);
-	exchange->df_a=mu*exchange->f_a/d_ij;
-
-	/* f_c, df_c calc (again, same for ij and ji) */
+	/* f_c, df_c */
 	if(d_ij<R) {
-		/* f_c = 1, df_c = 0 */
 		f_c=1.0;
 		df_c=0.0;
-		/* two body contribution (ij, ji) */
 		v3_scale(&force,&dist_ij,-df_r);
 	}
 	else {
@@ -199,509 +197,456 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 		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));
-		/* two body contribution (ij, ji) */
 		v3_scale(&force,&dist_ij,-df_c*f_r-df_r*f_c);
-		/* tell 3bp that S > r > R */
-		exchange->d_ij_between_rs=1;
 	}
 
-	/* add forces of 2bp (ij, ji) contribution
-	 * dVij = dVji and we sum up both: no 1/2) */
+	/* add forces */
 	v3_add(&(ai->f),&(ai->f),&force);
-
-	/* virial */
-	ai->virial.xx-=force.x*dist_ij.x;
-	ai->virial.yy-=force.y*dist_ij.y;
-	ai->virial.zz-=force.z*dist_ij.z;
-	ai->virial.xy-=force.x*dist_ij.y;
-	ai->virial.xz-=force.x*dist_ij.z;
-	ai->virial.yz-=force.y*dist_ij.z;
+	v3_scale(&force,&force,-1.0); // reason: dri rij = - drj rij
+	v3_add(&(aj->f),&(aj->f),&force);
 
 #ifdef DEBUG
-if(ai==&(moldyn->atom[0])) {
-	printf("dVij, dVji (2bp) contrib:\n");
-	printf("%f | %f\n",force.x,ai->f.x);
-	printf("%f | %f\n",force.y,ai->f.y);
-	printf("%f | %f\n",force.z,ai->f.z);
-}
-#endif
-#ifdef VDEBUG
-if(ai==&(moldyn->atom[0])) {
-	printf("dVij, dVji (2bp) contrib:\n");
-	printf("%f | %f\n",force.x*dist_ij.x,ai->virial.xx);
-	printf("%f | %f\n",force.y*dist_ij.y,ai->virial.yy);
-	printf("%f | %f\n",force.z*dist_ij.z,ai->virial.zz);
-}
+	if((ai==&(moldyn->atom[0]))|(aj==&(moldyn->atom[0]))) {
+		printf("force 2bp: [%d %d]\n",ai->tag,aj->tag);
+		printf("adding %f %f %f\n",force.x,force.y,force.z);
+		if(ai==&(moldyn->atom[0]))
+			printf("total i: %f %f %f\n",ai->f.x,ai->f.y,ai->f.z);
+		if(aj==&(moldyn->atom[0]))
+			printf("total j: %f %f %f\n",aj->f.x,aj->f.y,aj->f.z);
+	}
 #endif
 
-	/* energy 2bp contribution (ij, ji) 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 and 2bp post processing */
-	exchange->run3bp=1;
-	exchange->run2bp_post=1;
+	/* virial */
+	virial_calc(ai,&force,&dist_ij);
 
-	/* reset 3bp sums */
-	exchange->zeta_ij=0.0;
-	exchange->zeta_ji=0.0;
-	v3_zero(&(exchange->dzeta_ij));
-	v3_zero(&(exchange->dzeta_ji));
+	/* energy 2bp contribution */
+	energy=f_r*f_c;
+	moldyn->energy+=energy;
+	ai->e+=0.5*energy;
+	aj->e+=0.5*energy;
 
 	return 0;
 }
 
-/* tersoff 2 body post part */
+/* tersoff 3 body potential function (first ij loop) */
+int tersoff_mult_3bp_j1(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 
-int tersoff_mult_post_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
+	t_tersoff_mult_params *params;
+	t_tersoff_exchange *exchange;
+	unsigned char brand;
+	double S2;
+	t_3dvec dist_ij;
+	double d_ij2,d_ij;
+
+	params=moldyn->pot_params;
+	exchange=&(params->exchange);
+
+	/* reset zeta sum */
+	exchange->zeta_ij=0.0;
 
 	/*
-	 * here we have to allow for the 3bp sums
-	 *
-	 * that is:
-	 * - zeta_ij, dzeta_ij
-	 * - zeta_ji, dzeta_ji
-	 *
-	 * to compute the 3bp contribution to:
-	 * - Vij, dVij
-	 * - dVji
-	 *
+	 * set ij depending values
 	 */
 
+	brand=ai->brand;
+	
+	if(brand==aj->brand)
+		S2=params->S2[brand];
+	else
+		S2=params->S2mixed;
+
+	/* dist_ij, d_ij2 */
+	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) {
+		moldyn->run3bp=0;
+		return 0;
+	}
+
+	/* d_ij */
+	d_ij=sqrt(d_ij2);
+
+	/* store values */
+	exchange->dist_ij=dist_ij;
+	exchange->d_ij2=d_ij2;
+	exchange->d_ij=d_ij;
+
+	/* reset k counter for first k loop */
+	exchange->kcount=0;
+		
+	return 0;
+}
+
+/* tersoff 3 body potential function (first k loop) */
+int tersoff_mult_3bp_k1(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 force,temp;
-	t_3dvec *dist_ij;
-	double b,db,tmp;
-	double f_c,df_c,f_a,df_a;
-	double chi,ni,betaini,nj,betajnj;
-	double zeta;
+	unsigned char brand;
+	double R,S,S2;
+	t_3dvec dist_ij,dist_ik;
+	double d_ik2,d_ik,d_ij;
+	double cos_theta,h_cos,d2_h_cos2,frac,g,dg,s_r,arg;
+	double f_c_ik,df_c_ik;
+	int kcount;
 
 	params=moldyn->pot_params;
 	exchange=&(params->exchange);
+	kcount=exchange->kcount;
 
-	/* we do not run if f_c_ij was detected to be 0! */
-	if(!(exchange->run2bp_post))
-		return 0;
+	if(kcount>TERSOFF_MAXN) {
+		printf("FATAL: neighbours = %d\n",kcount);
+		printf("  -> %d %d %d\n",ai->tag,aj->tag,ak->tag);
+	}
 
-	f_c=exchange->f_c;
-	df_c=exchange->df_c;
-	f_a=exchange->f_a;
-	df_a=exchange->df_a;
-	betaini=exchange->betaini;
-	betajnj=exchange->betajnj;
-	ni=*(exchange->n_i);
-	nj=*(exchange->n_j);
-	chi=exchange->chi;
-	dist_ij=&(exchange->dist_ij);
-	
-	/* Vij and dVij */
-	zeta=exchange->zeta_ij;
-	if(zeta==0.0) {
-		moldyn->debug++;		/* just for debugging ... */
-		b=chi;
-		v3_scale(&force,dist_ij,df_a*b*f_c);
+	/* ik constants */
+	brand=ai->brand;
+	if(brand==ak->brand) {
+		R=params->R[brand];
+		S=params->S[brand];
+		S2=params->S2[brand];
 	}
 	else {
-		tmp=betaini*pow(zeta,ni-1.0);		/* beta^n * zeta^n-1 */
-		b=(1+zeta*tmp);				/* 1 + beta^n zeta^n */
-		db=chi*pow(b,-1.0/(2*ni)-1);		/* x(...)^(-1/2n - 1) */
-		b=db*b;					/* b_ij */
-		db*=-0.5*tmp;				/* db_ij */
-		v3_scale(&force,&(exchange->dzeta_ij),f_a*db);
-		v3_scale(&temp,dist_ij,df_a*b);
-		v3_add(&force,&force,&temp);
-		v3_scale(&force,&force,f_c);
+		R=params->Rmixed;
+		S=params->Smixed;
+		S2=params->S2mixed;
 	}
-	v3_scale(&temp,dist_ij,df_c*b*f_a);
-	v3_add(&force,&force,&temp);
-	v3_scale(&force,&force,-0.5);
 
-	/* add force */
-	v3_add(&(ai->f),&(ai->f),&force);
+	/* dist_ik, d_ik2 */
+	v3_sub(&dist_ik,&(ak->r),&(ai->r));
+	if(bc) check_per_bound(moldyn,&dist_ik);
+	d_ik2=v3_absolute_square(&dist_ik);
 
-	/* virial */
-	ai->virial.xx-=force.x*dist_ij->x;
-	ai->virial.yy-=force.y*dist_ij->y;
-	ai->virial.zz-=force.z*dist_ij->z;
-	ai->virial.xy-=force.x*dist_ij->y;
-	ai->virial.xz-=force.x*dist_ij->z;
-	ai->virial.yz-=force.y*dist_ij->z;
+	/* store data for second k loop */
+	exchange->dist_ik[kcount]=dist_ik;
+	exchange->d_ik2[kcount]=d_ik2;
+
+	/* return if not within cutoff */
+	if(d_ik2>S2) {
+		exchange->kcount++;
+		return 0;
+	}
+
+	/* d_ik */
+	d_ik=sqrt(d_ik2);
+
+	/* dist_ij, d_ij */
+	dist_ij=exchange->dist_ij;
+	d_ij=exchange->d_ij;
+
+	/* cos theta */
+	cos_theta=v3_scalar_product(&dist_ij,&dist_ik)/(d_ij*d_ik);
+
+	/* g_ijk */
+	h_cos=params->h[brand]-cos_theta;
+	d2_h_cos2=params->di2[brand]+(h_cos*h_cos);
+	frac=params->ci2[brand]/d2_h_cos2;
+	g=1.0+params->ci2di2[brand]-frac;
+	dg=-2.0*frac*h_cos/d2_h_cos2;
+
+	/* zeta sum += f_c_ik * g_ijk */
+	if(d_ik<=R) {
+		exchange->zeta_ij+=g;
+		f_c_ik=1.0;
+		df_c_ik=0.0;
+	}
+	else {
+		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));
+		exchange->zeta_ij+=f_c_ik*g;
+	}
 
 #ifdef DEBUG
-if(ai==&(moldyn->atom[0])) {
-	printf("dVij (3bp) contrib:\n");
-	printf("%f | %f\n",force.x,ai->f.x);
-	printf("%f | %f\n",force.y,ai->f.y);
-	printf("%f | %f\n",force.z,ai->f.z);
-}
+	if(ai==&(moldyn->atom[DATOM]))
+		printf("zeta_ij: %f %f %f %f\n",f_c_ik*g,f_c_ik,g,d_ik);
 #endif
-#ifdef VDEBUG
-if(ai==&(moldyn->atom[0])) {
-	printf("dVij (3bp) contrib:\n");
-	printf("%f | %f\n",force.x*dist_ij->x,ai->virial.xx);
-	printf("%f | %f\n",force.y*dist_ij->y,ai->virial.yy);
-	printf("%f | %f\n",force.z*dist_ij->z,ai->virial.zz);
+
+	/* store even more data for second k loop */
+	exchange->g[kcount]=g;
+	exchange->dg[kcount]=dg;
+	exchange->d_ik[kcount]=d_ik;
+	exchange->cos_theta[kcount]=cos_theta;
+	exchange->f_c_ik[kcount]=f_c_ik;
+	exchange->df_c_ik[kcount]=df_c_ik;
+
+	/* increase k counter */
+	exchange->kcount++;
+
+	return 0;
 }
-#endif
 
-	/* add energy of 3bp sum */
-	moldyn->energy+=(0.5*f_c*b*f_a);
+int tersoff_mult_3bp_j2(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
+
+	t_tersoff_mult_params *params;
+	t_tersoff_exchange *exchange;
+	t_3dvec force;
+	double f_a,df_a,b,db,f_c,df_c;
+	double f_r,df_r;
+	double scale;
+	double mu,B,chi;
+	double lambda,A;
+	double d_ij;
+	unsigned char brand;
+	double ni,tmp;
+	double S,R,s_r,arg;
+	double energy;
 
-	/* dVji */
-	zeta=exchange->zeta_ji;
-	if(zeta==0.0) {
-		moldyn->debug++;
+	params=moldyn->pot_params;
+	exchange=&(params->exchange);
+
+	brand=ai->brand;
+	if(brand==aj->brand) {
+		S=params->S[brand];
+		R=params->R[brand];
+		B=params->B[brand];
+		A=params->A[brand];
+		mu=params->mu[brand];
+		lambda=params->lambda[brand];
+		chi=1.0;
+	}
+	else {
+		S=params->Smixed;
+		R=params->Rmixed;
+		B=params->Bmixed;
+		A=params->Amixed;
+		mu=params->mu_m;
+		lambda=params->lambda_m;
+		chi=params->chi;
+	}
+
+	d_ij=exchange->d_ij;
+
+	/* f_c, df_c */
+	if(d_ij<R) {
+		f_c=1.0;
+		df_c=0.0;
+	}
+	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));
+	}
+
+	/* f_a, df_a */
+	f_a=-B*exp(-mu*d_ij);
+	df_a=mu*f_a/d_ij;
+
+	/* f_r, df_r */
+	f_r=A*exp(-lambda*d_ij);
+	df_r=lambda*f_r/d_ij;
+
+	/* b, db */
+	if(exchange->zeta_ij==0.0) {
 		b=chi;
-		v3_scale(&force,dist_ij,df_a*b*f_c);
+		db=0.0;
 	}
 	else {
-		tmp=betajnj*pow(zeta,nj-1.0);		/* beta^n * zeta^n-1 */
-		b=(1+zeta*tmp);				/* 1 + beta^n zeta^n */
-		db=chi*pow(b,-1.0/(2*nj)-1);		/* x(...)^(-1/2n - 1) */
-		b=db*b;					/* b_ij */
-		db*=-0.5*tmp;				/* db_ij */
-		v3_scale(&force,&(exchange->dzeta_ji),f_a*db);
-		v3_scale(&temp,dist_ij,df_a*b);
-		v3_add(&force,&force,&temp);
-		v3_scale(&force,&force,f_c);
+		ni=params->n[brand];
+		tmp=params->betaini[brand]*pow(exchange->zeta_ij,ni-1.0);
+		b=(1.0+exchange->zeta_ij*tmp);
+		db=chi*pow(b,-1.0/(2.0*ni)-1.0);
+		b=db*b;
+		db*=-0.5*tmp;
 	}
-	v3_scale(&temp,dist_ij,df_c*b*f_a);
-	v3_add(&force,&force,&temp);
-	v3_scale(&force,&force,-0.5);
 
-	/* add force */
+	/* force contribution */
+	scale=-0.5*(f_c*(df_r+b*df_a)+df_c*(f_r+b*df_a));
+	v3_scale(&force,&(exchange->dist_ij),scale);
 	v3_add(&(ai->f),&(ai->f),&force);
-
-	/* virial - plus sign, as dist_ij = - dist_ji - (really??) */
-// TEST ... with a minus instead
-	ai->virial.xx-=force.x*dist_ij->x;
-	ai->virial.yy-=force.y*dist_ij->y;
-	ai->virial.zz-=force.z*dist_ij->z;
-	ai->virial.xy-=force.x*dist_ij->y;
-	ai->virial.xz-=force.x*dist_ij->z;
-	ai->virial.yz-=force.y*dist_ij->z;
+	v3_scale(&force,&force,-1.0); // dri rij = - drj rij
+	v3_add(&(aj->f),&(aj->f),&force);
 
 #ifdef DEBUG
-if(ai==&(moldyn->atom[0])) {
-	printf("dVji (3bp) contrib:\n");
-	printf("%f | %f\n",force.x,ai->f.x);
-	printf("%f | %f\n",force.y,ai->f.y);
-	printf("%f | %f\n",force.z,ai->f.z);
-}
-#endif
-#ifdef VDEBUG
-if(ai==&(moldyn->atom[0])) {
-	printf("dVji (3bp) contrib:\n");
-	printf("%f | %f\n",force.x*dist_ij->x,ai->virial.xx);
-	printf("%f | %f\n",force.y*dist_ij->y,ai->virial.yy);
-	printf("%f | %f\n",force.z*dist_ij->z,ai->virial.zz);
-}
+	if((ai==&(moldyn->atom[DATOM]))|(aj==&(moldyn->atom[DATOM]))) {
+		printf("force 3bp (j2): [%d %d sum]\n",ai->tag,aj->tag);
+		printf("adding %f %f %f\n",force.x,force.y,force.z);
+		if(ai==&(moldyn->atom[DATOM]))
+			printf("total i: %f %f %f\n",ai->f.x,ai->f.y,ai->f.z);
+		if(aj==&(moldyn->atom[DATOM]))
+			printf("total j: %f %f %f\n",aj->f.x,aj->f.y,aj->f.z);
+		printf("energy: %f = %f %f %f %f\n",0.5*f_c*(b*f_a+f_r),
+		                                    f_c,b,f_a,f_r);
+		printf("        %f %f %f\n",exchange->zeta_ij,.0,.0);
+	}
 #endif
 
+	/* virial */
+	virial_calc(ai,&force,&(exchange->dist_ij));
+
+	/* dzeta prefactor = - 0.5 f_c f_a db */
+	exchange->pre_dzeta=-0.5*f_a*f_c*db;
+
+	/* energy contribution */
+	energy=0.5*f_c*(b*f_a+f_r);
+	moldyn->energy+=energy;
+	ai->e+=energy;
+
+	/* reset k counter for second k loop */
+	exchange->kcount=0;
+		
 	return 0;
 }
 
-/* tersoff 3 body part */
-
-int tersoff_mult_3bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,t_atom *ak,u8 bc) {
+/* tersoff 3 body potential function (second k loop) */
+int tersoff_mult_3bp_k2(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 temp1,temp2;
-	t_3dvec *dzeta;
-	double R,S,S2,s_r;
-	double B,mu;
-	double d_ij,d_ik,d_jk,d_ij2,d_ik2,d_jk2;
-	double rr,dd;
-	double f_c,df_c;
-	double f_c_ik,df_c_ik,arg;
-	double f_c_jk;
-	double n,c,d,h;
-	double c2,d2,c2d2;
-	double cos_theta,d_costheta1,d_costheta2;
-	double h_cos,d2_h_cos2;
-	double frac,g,zeta,chi;
-	double tmp;
-	int brand;
+	int kcount;
+	t_3dvec dist_ik,dist_ij;
+	double d_ik2,d_ik,d_ij2,d_ij;
+	unsigned char brand;
+	double S2;
+	double g,dg,cos_theta;
+	double pre_dzeta;
+	double f_c_ik,df_c_ik;
+	double dijdik_inv,fcdg,dfcg;
+	t_3dvec dcosdrj,dcosdrk;
+	t_3dvec force,tmp;
 
 	params=moldyn->pot_params;
 	exchange=&(params->exchange);
+	kcount=exchange->kcount;
+
+	if(kcount>TERSOFF_MAXN)
+		printf("FATAL: neighbours!\n");
+
+	/* d_ik2 */
+	d_ik2=exchange->d_ik2[kcount];
 
-	if(!(exchange->run3bp))
+	brand=ak->brand;
+	if(brand==ai->brand)
+		S2=params->S2[brand];
+	else
+		S2=params->S2mixed;
+
+	/* return if d_ik > S */
+	if(d_ik2>S2) {
+		exchange->kcount++;
 		return 0;
+	}
 
-	/*
-	 * calc of 3bp contribution of V_ij and dV_ij/ji/jk &
-	 * 2bp contribution of dV_jk
-	 *
-	 * for Vij and dV_ij we still need:
-	 * - b_ij, db_ij (zeta_ij)
-	 *   - f_c_ik, df_c_ik, constants_i, cos_theta_ijk, d_costheta_ijk
-	 *
-	 * for dV_ji we still need:
-	 * - b_ji, db_ji (zeta_ji)
-	 *   - f_c_jk, d_c_jk, constants_j, cos_theta_jik, d_costheta_jik
-	 *
-	 * for dV_jk we need:
-	 * - f_c_jk
-	 * - f_a_jk
-	 * - db_jk (zeta_jk)
-	 *   - f_c_ji, df_c_ji, constants_j, cos_theta_jki, d_costheta_jki
-	 *
-	 */
+	/* prefactor dzeta */
+	pre_dzeta=exchange->pre_dzeta;
 
-	/*
-	 * get exchange data 
-	 */
+	/* dist_ik, d_ik */
+	dist_ik=exchange->dist_ik[kcount];
+	d_ik=exchange->d_ik[kcount];
 
-	/* dist_ij, d_ij - this is < S_ij ! */
+	/* f_c_ik, df_c_ik */
+	f_c_ik=exchange->f_c_ik[kcount];
+	df_c_ik=exchange->df_c_ik[kcount];
+
+	/* dist_ij, d_ij2, d_ij */
 	dist_ij=exchange->dist_ij;
-	d_ij=exchange->d_ij;
 	d_ij2=exchange->d_ij2;
+	d_ij=exchange->d_ij;
 
-	/* f_c_ij, df_c_ij (same for ji) */
-	f_c=exchange->f_c;
-	df_c=exchange->df_c;
+	/* g, dg, cos_theta */
+	g=exchange->g[kcount];
+	dg=exchange->dg[kcount];
+	cos_theta=exchange->cos_theta[kcount];
 
-	/*
-	 * calculate unknown values now ...
-	 */
+	/* cos_theta derivatives wrt i,j,k */
+	dijdik_inv=1.0/(d_ij*d_ik);
+	v3_scale(&dcosdrj,&dist_ik,dijdik_inv);
+	v3_scale(&tmp,&dist_ij,-cos_theta/d_ij2);
+	v3_add(&dcosdrj,&dcosdrj,&tmp);
+	v3_scale(&dcosdrk,&dist_ij,dijdik_inv);
+	v3_scale(&tmp,&dist_ik,-cos_theta/d_ik2);
+	v3_add(&dcosdrk,&dcosdrk,&tmp);
 
-	/* V_ij and dV_ij stuff (in b_ij there is f_c_ik) */
+	/* f_c_ik * dg, df_c_ik * g */
+	fcdg=f_c_ik*dg;
+	dfcg=df_c_ik*g;
 
-	/* dist_ik, d_ik */
-	v3_sub(&dist_ik,&(ak->r),&(ai->r));
-	if(bc) check_per_bound(moldyn,&dist_ik);
-	d_ik2=v3_absolute_square(&dist_ik);
+	/* derivative wrt j */
+	v3_scale(&force,&dcosdrj,fcdg*pre_dzeta);
 
-	/* ik constants */
-	brand=ai->brand;
-	if(brand==ak->brand) {
-		R=params->R[brand];
-		S=params->S[brand];
-		S2=params->S2[brand];
-	}
-	else {
-		R=params->Rmixed;
-		S=params->Smixed;
-		S2=params->S2mixed;
-	}
+	/* force contribution */
+	v3_add(&(aj->f),&(aj->f),&force);
 
-	/* zeta_ij/dzeta_ij contribution only for d_ik < S */
-	if(d_ik2<S2) {
-
-		/* now we need d_ik */
-		d_ik=sqrt(d_ik2);
-
-		/* 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_ij2-tmp;
-		d_costheta2=cos_theta/d_ik2-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));
-
-			/* 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);
-		}
+#ifdef DEBUG
+	if(aj==&(moldyn->atom[DATOM])) {
+		printf("force 3bp (k2): [%d %d %d]\n",ai->tag,aj->tag,ak->tag);
+		printf("  adding %f %f %f\n",force.x,force.y,force.z);
+		printf("  total j: %f %f %f\n",aj->f.x,aj->f.y,aj->f.z);
+		printf("  angle: %f\n",acos(cos_theta)*360.0/(2*M_PI));
+		printf("    d ij ik = %f %f\n",d_ij,d_ik);
 	}
+#endif
 
-	/* dV_ji stuff (in b_ji there is f_c_jk) + dV_jk stuff! */
+	/* virial */
+	virial_calc(ai,&force,&dist_ij);
 
-	/* dist_jk, d_jk */
-	v3_sub(&dist_jk,&(ak->r),&(aj->r));
-	if(bc) check_per_bound(moldyn,&dist_jk);
-	d_jk2=v3_absolute_square(&dist_jk);
+	/* force contribution to atom i */
+	v3_scale(&force,&force,-1.0);
+	v3_add(&(ai->f),&(ai->f),&force);
 
-	/* jk constants */
-	brand=aj->brand;
-	if(brand==ak->brand) {
-		R=params->R[brand];
-		S=params->S[brand];
-		S2=params->S2[brand];
-		B=params->B[brand];
-		mu=params->mu[brand];
-		chi=1.0;
-	}
-	else {
-		R=params->Rmixed;
-		S=params->Smixed;
-		S2=params->S2mixed;
-		B=params->Bmixed;
-		mu=params->mu_m;
-		chi=params->chi;
-	}
+	/* derivative wrt k */
+	v3_scale(&force,&dist_ik,-1.0*dfcg); // dri rik = - drk rik
+	v3_scale(&tmp,&dcosdrk,fcdg);
+	v3_add(&force,&force,&tmp);
+	v3_scale(&force,&force,pre_dzeta);
 
-	/* zeta_ji/dzeta_ji contribution only for d_jk < S_jk */
-	if(d_jk2<S2) {
-
-		/* now we need d_ik */
-		d_jk=sqrt(d_jk2);
-
-		/* 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_ij2;
-
-		/* 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_jik 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_sub(&temp1,&temp1,&temp2); /* there is a minus! */
-		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 ^ */
-
-		/* virial */
-		ai->virial.xx-=temp2.x*dist_jk.x;
-		ai->virial.yy-=temp2.y*dist_jk.y;
-		ai->virial.zz-=temp2.z*dist_jk.z;
-		ai->virial.xy-=temp2.x*dist_jk.y;
-		ai->virial.xz-=temp2.x*dist_jk.z;
-		ai->virial.yz-=temp2.y*dist_jk.z;
+	/* force contribution */
+	v3_add(&(ak->f),&(ak->f),&force);
 
 #ifdef DEBUG
-if(ai==&(moldyn->atom[0])) {
-	printf("dVjk (3bp) contrib:\n");
-	printf("%f | %f\n",temp2.x,ai->f.x);
-	printf("%f | %f\n",temp2.y,ai->f.y);
-	printf("%f | %f\n",temp2.z,ai->f.z);
-}
+	if(ak==&(moldyn->atom[DATOM])) {
+		printf("force 3bp (k2): [%d %d %d]\n",ai->tag,aj->tag,ak->tag);
+		printf("  adding %f %f %f\n",force.x,force.y,force.z);
+		printf("  total k: %f %f %f\n",ak->f.x,ak->f.y,ak->f.z);
+		printf("  angle: %f\n",acos(cos_theta)*360.0/(2*M_PI));
+		printf("    d ij ik = %f %f\n",d_ij,d_ik);
+	}
 #endif
-#ifdef VDEBUG
-if(ai==&(moldyn->atom[0])) {
-	printf("dVjk (3bp) contrib:\n");
-	printf("%f | %f\n",temp2.x*dist_jk.x,ai->virial.xx);
-	printf("%f | %f\n",temp2.y*dist_jk.y,ai->virial.yy);
-	printf("%f | %f\n",temp2.z*dist_jk.z,ai->virial.zz);
+
+	/* virial */
+	virial_calc(ai,&force,&dist_ik);
+
+	/* force contribution to atom i */
+	v3_scale(&force,&force,-1.0);
+	v3_add(&(ai->f),&(ai->f),&force);
+	
+	/* increase k counter */
+	exchange->kcount++;
+
+	return 0;
+
 }
-#endif
 
+int tersoff_mult_check_2b_bond(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
+
+	t_tersoff_mult_params *params;
+	t_3dvec dist;
+	double d;
+	u8 brand;
+
+	v3_sub(&dist,&(aj->r),&(ai->r));
+	if(bc) check_per_bound(moldyn,&dist);
+	d=v3_absolute_square(&dist);
+
+	params=moldyn->pot_params;
+	brand=ai->brand;
+
+	if(brand==aj->brand) {
+		if(d<=params->S2[brand])
+			return TRUE;
+	}
+	else {
+		if(d<=params->S2mixed)
+			return TRUE;
 	}
 
-	return 0;
+	return FALSE;
 }