X-Git-Url: https://www.hackdaworld.org/gitweb/?a=blobdiff_plain;f=moldyn.c;h=f09c93a27e10fb00dc7a4dc6087bb1cb3f921948;hb=0acbade9c8d1ed354c333955dc2c5575540a9236;hp=f504e6854302093297620c50eb9ed67e3f770cfa;hpb=000e702c884e337f27ae66b6506ff9f9b613f8a8;p=physik%2Fposic.git

diff --git a/moldyn.c b/moldyn.c
index f504e68..f09c93a 100644
--- a/moldyn.c
+++ b/moldyn.c
@@ -139,6 +139,14 @@ int set_potential2b(t_moldyn *moldyn,pf_func2b func,void *params) {
 	return 0;
 }
 
+int set_potential2b_post(t_moldyn *moldyn,pf_func2b_post func,void *params) {
+
+	moldyn->func2b_post=func;
+	moldyn->pot2b_params=params;
+
+	return 0;
+}
+
 int set_potential3b(t_moldyn *moldyn,pf_func3b func,void *params) {
 
 	moldyn->func3b=func;
@@ -568,9 +576,8 @@ int link_cell_neighbour_index(t_moldyn *moldyn,int i,int j,int k,t_list *cell) {
 	}
 
 	lc->dnlc=count1;
-	lc->countn=27;
 
-	return count2;
+	return count1;
 }
 
 int link_cell_shutdown(t_moldyn *moldyn) {
@@ -656,10 +663,11 @@ int moldyn_integrate(t_moldyn *moldyn) {
 	/* sqaure of some variables */
 	moldyn->tau_square=moldyn->tau*moldyn->tau;
 	moldyn->cutoff_square=moldyn->cutoff*moldyn->cutoff;
+
 	/* calculate initial forces */
 	potential_force_calc(moldyn);
 
-	/* do some checks before we actually start calculating bullshit */
+	/* some stupid checks before we actually start calculating bullshit */
 	if(moldyn->cutoff>0.5*moldyn->dim.x)
 		printf("[moldyn] warning: cutoff > 0.5 x dim.x\n");
 	if(moldyn->cutoff>0.5*moldyn->dim.y)
@@ -672,6 +680,11 @@ int moldyn_integrate(t_moldyn *moldyn) {
 
 	/* zero absolute time */
 	moldyn->time=0.0;
+
+	/* debugging, ignre */
+	moldyn->debug=0;
+
+	/* executing the schedule */
 	for(sched=0;sched<moldyn->schedule.content_count;sched++) {
 
 		/* setting amount of runs and finite time step size */
@@ -684,6 +697,7 @@ int moldyn_integrate(t_moldyn *moldyn) {
 	for(i=0;i<moldyn->time_steps;i++) {
 
 		/* integration step */
+printf("MOVE\n");
 		moldyn->integrate(moldyn);
 
 		/* p/t scaling */
@@ -728,7 +742,8 @@ int moldyn_integrate(t_moldyn *moldyn) {
 			if(!(i%v)) {
 				visual_atoms(&(moldyn->vis),moldyn->time,
 				             moldyn->atom,moldyn->count);
-				printf("\rsched: %d, steps: %d",sched,i);
+				printf("\rsched: %d, steps: %d, theta: %d",
+				       sched,i,moldyn->debug);
 				fflush(stdout);
 			}
 		}
@@ -739,6 +754,9 @@ int moldyn_integrate(t_moldyn *moldyn) {
 		if(schedule->hook)
 			schedule->hook(moldyn,schedule->hook_params);
 
+		/* get a new info line */
+		printf("\n");
+
 	}
 
 	return 0;
@@ -776,7 +794,6 @@ int velocity_verlet(t_moldyn *moldyn) {
 
 	/* forces depending on chosen potential */
 	potential_force_calc(moldyn);
-	//moldyn->potential_force_function(moldyn);
 
 	for(i=0;i<count;i++) {
 		/* again velocities */
@@ -805,8 +822,8 @@ int potential_force_calc(t_moldyn *moldyn) {
 	t_list neighbour_i2[27];
 	//t_list neighbour_j[27];
 	t_list *this,*that;
-	u8 bc_ij,bc_ijk;
-	int countn,dnlc;
+	u8 bc_ij,bc_ik;
+	int dnlc;
 
 	count=moldyn->count;
 	itom=moldyn->atom;
@@ -815,6 +832,7 @@ int potential_force_calc(t_moldyn *moldyn) {
 	/* reset energy */
 	moldyn->energy=0.0;
 
+	/* get energy and force of every atom */
 	for(i=0;i<count;i++) {
 
 		/* reset force */
@@ -833,10 +851,9 @@ int potential_force_calc(t_moldyn *moldyn) {
 				(itom[i].r.z+moldyn->dim.z/2)/lc->z,
 				neighbour_i);
 
-			countn=lc->countn;
 			dnlc=lc->dnlc;
 
-			for(j=0;j<countn;j++) {
+			for(j=0;j<27;j++) {
 
 				this=&(neighbour_i[j]);
 				list_reset(this);
@@ -865,59 +882,12 @@ int potential_force_calc(t_moldyn *moldyn) {
 					   !(jtom->attr&ATOM_ATTR_3BP))
 						continue;
 
-			/*
-			 * according to mr. nordlund, we dont need to take the 
-			 * sum over all atoms now, as 'this is centered' around
-			 * atom i ...
-			 * i am not quite sure though! there is a not vanishing
-			 * part even if f_c_ik is zero ...
-			 * this analytical potentials suck!
-			 * switching from mc to md to dft soon!
-			 */
-
-			//		link_cell_neighbour_index(moldyn,
-			//		   (jtom->r.x+moldyn->dim.x/2)/lc->x,
-			//		   (jtom->r.y+moldyn->dim.y/2)/lc->y,
-			//		   (jtom->r.z+moldyn->dim.z/2)/lc->z,
-			//		   neighbour_j);
-
-//					/* neighbours of j */
-//					for(k=0;k<lc->countn;k++) {
-//
-//						that=&(neighbour_j[k]);
-//						list_reset(that);
-//					
-//						if(that->start==NULL)
-//							continue;
-//
-//						bc_ijk=(k<lc->dnlc)?0:1;
-//
-//						do {
-//
-//			ktom=that->current->data;
-//
-//			if(!(ktom->attr&ATOM_ATTR_3BP))
-//				continue;
-//
-//			if(ktom==jtom)
-//				continue;
-//
-//			if(ktom==&(itom[i]))
-//				continue;
-//
-//			moldyn->func3b(moldyn,&(itom[i]),jtom,ktom,bc_ijk);
-//
-/*						} while(list_next(that)!=\ */
-//						        L_NO_NEXT_ELEMENT);
-//
-//					}
-			
 					/* copy the neighbour lists */
 					memcpy(neighbour_i2,neighbour_i,
 					       27*sizeof(t_list));
 
 					/* get neighbours of i */
-					for(k=0;k<countn;k++) {
+					for(k=0;k<27;k++) {
 
 						that=&(neighbour_i2[k]);
 						list_reset(that);
@@ -925,7 +895,7 @@ int potential_force_calc(t_moldyn *moldyn) {
 						if(that->start==NULL)
 							continue;
 
-						bc_ijk=(k<dnlc)?0:1;
+						bc_ik=(k<dnlc)?0:1;
 
 						do {
 
@@ -940,9 +910,7 @@ int potential_force_calc(t_moldyn *moldyn) {
 			if(ktom==&(itom[i]))
 				continue;
 
-printf("Debug: atom %d before 3bp: %08x %08x %08x | %.15f %.15f %.15f\n",i,&itom[i],jtom,ktom,itom[i].r.x,itom[i].f.x,itom[i].v.x);
-			moldyn->func3b(moldyn,&(itom[i]),jtom,ktom,bc_ijk);
-printf("Debug: atom %d after 3bp: %08x %08x %08x | %.15f %.15f %.15f\n",i,&itom[i],jtom,ktom,itom[i].r.x,itom[i].f.x,itom[i].v.x);
+			moldyn->func3b(moldyn,&(itom[i]),jtom,ktom,bc_ik|bc_ij);
 
 						} while(list_next(that)!=\
 						        L_NO_NEXT_ELEMENT);
@@ -950,8 +918,17 @@ printf("Debug: atom %d after 3bp: %08x %08x %08x | %.15f %.15f %.15f\n",i,&itom[
 					}
 					
 				} while(list_next(this)!=L_NO_NEXT_ELEMENT);
+		
+				/* 2bp post function */
+				if(moldyn->func2b_post) {
+					moldyn->func2b_post(moldyn,
+					                    &(itom[i]),
+					                    jtom,bc_ij);
+				}
+
 			}
 		}
+printf("debug atom %d: %.15f %.15f %.15f\n",i,itom[i].r.x,itom[i].v.x,itom[i].f.x);
 	}
 
 	return 0;
@@ -1072,6 +1049,21 @@ int tersoff_mult_complete_params(t_tersoff_mult_params *p) {
 	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;
 }
 
@@ -1098,6 +1090,7 @@ int tersoff_mult_1bp(t_moldyn *moldyn,t_atom *ai) {
 	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;
@@ -1125,6 +1118,7 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 	exchange=&(params->exchange);
 
 	exchange->run3bp=0;
+	exchange->run2bp_post=0;
 	
 	/*
 	 * we need: f_c, df_c, f_r, df_r
@@ -1141,7 +1135,6 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 	/* 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) {
@@ -1162,14 +1155,13 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 		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 */
+	/* f_a, df_a calc + save for later use */
 	exchange->f_a=-B*exp(-mu*d_ij);
 	exchange->df_a=-mu*exchange->f_a/d_ij;
 
@@ -1197,8 +1189,78 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 	exchange->f_c=f_c;
 	exchange->df_c=df_c;
 
-	/* enable the run of 3bp function */
+	/* enable the run of 3bp function and 2bp post processing */
 	exchange->run3bp=1;
+	exchange->run2bp_post=1;
+
+	/* reset 3bp sums */
+	exchange->zeta=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,n,n_betan;
+	double zeta;
+
+	params=moldyn->pot2b_params;
+	exchange=&(params->exchange);
+
+	/* we do not run if f_c_ij was detected to be 0! */
+	if(!(exchange->run2bp_post))
+		return 0;
+
+	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;
+	n_betan=exchange->n_betan;
+	n=*(exchange->n);
+	chi=exchange->chi;
+	dist_ij=&(exchange->dist_ij);
+	zeta=exchange->zeta;
+
+	db_ij_scale2=pow(zeta,n-1.0);
+printf("DEBUG: %.15f %.15f\n",zeta,db_ij_scale2);
+	db_ij_scale1=db_ij_scale2*zeta;
+	db_ij_scale2*=n_betan;
+	db_ij_scale1=pow((1.0+n_betan*db_ij_scale1),-1.0/(2*n)-1);
+	b_ij=chi*db_ij_scale1*(1.0+n_betan*db_ij_scale1);
+	db_ij_scale1*=(-1.0*chi/(2*n));
+
+	/* db_ij part */
+	v3_scale(db_ij,db_ij,(db_ij_scale1*db_ij_scale2));
+	v3_scale(db_ij,db_ij,f_a);
+
+	/* df_a part */
+	v3_scale(&temp,dist_ij,b_ij*df_a);
+
+	/* db_ij + df_a part */
+	v3_add(&force,&temp,db_ij);
+	v3_scale(&force,&force,f_c);
+
+	/* df_c part */
+	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 (all three parts) */
+	v3_add(&(ai->f),&temp,&force);
 
 	return 0;
 }
@@ -1209,22 +1271,19 @@ 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 dist_ij,dist_ik;
 	t_3dvec temp,force;
 	double R,S,s_r;
-	double d_ij,d_ij2,d_ik,d_jk;
-	double f_c,df_c,b_ij,f_a,df_a;
+	double d_ij,d_ik;
+	double rijrik,dijdik;
+	double f_c,df_c,f_a,df_a;
 	double f_c_ik,df_c_ik,arg;
-	double scale;
-	double chi;
-	double n,c,d,h,beta,betan;
+	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,h_cos2,d2_h_cos2;
-	double frac1,bracket1,bracket2,bracket2_n_1,bracket2_n;
-	double bracket3,bracket3_pow_1,bracket3_pow;
+	double cos_theta,d_costheta1,d_costheta2;
+	double h_cos,d2_h_cos2;
+	double frac;
+	double g;
 	int num;
 
 	params=moldyn->pot3b_params;
@@ -1241,10 +1300,13 @@ int tersoff_mult_3bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,t_atom *ak,u8 bc) {
 	 */
 
 	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! */
 
@@ -1253,8 +1315,7 @@ int tersoff_mult_3bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,t_atom *ak,u8 bc) {
 	 *
 	 * - 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,
+	 * - for db_ij: d_costheta, cos_theta, f_c_ik, df_c_ik, w_ik
 	 *
 	 */
 
@@ -1262,7 +1323,7 @@ int tersoff_mult_3bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,t_atom *ak,u8 bc) {
 	if(bc) check_per_bound(moldyn,&dist_ik);
 	d_ik=v3_norm(&dist_ik);
 
-	/* constants for f_c_ik calc */
+	/* constants */
 	if(num==ak->bnum) {
 		R=params->R[num];
 		S=params->S[num];
@@ -1272,105 +1333,83 @@ int tersoff_mult_3bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,t_atom *ak,u8 bc) {
 		S=params->Smixed;
 	}
 
-	/* calc of f_c_ik */
-	if(d_ik>S) {
-		f_c_ik=0.0;
-		df_c_ik=0.0;
-	}
-	else if(d_ik<R) {
-		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));
-	}
-	
-	v3_sub(&dist_jk,&(aj->r),&(ak->r));
-	if(bc) check_per_bound(moldyn,&dist_jk);
-	d_jk=v3_norm(&dist_jk);
+	/* there is no contribution if f_c_ik = 0 */
+	if(d_ik>S)
+		return 0;
 
-	beta=*(exchange->beta);
-	betan=exchange->betan;
+	/* get exchange data */
 	n=*(exchange->n);
 	c=*(exchange->c);
 	d=*(exchange->d);
 	h=*(exchange->h);
-	chi=exchange->chi;
 	c2=exchange->c2;
 	d2=exchange->d2;
 	c2d2=exchange->c2d2;
 
-	numer=d_ij2+d_ik*d_ik-d_jk*d_jk;
-	denom=2*d_ij*d_ik;
-	//cos_theta=numer/denom;
-	cos_theta=v3_scalar_product(&dist_ij,&dist_ik)/(d_ij*d_ik);
-	sin_theta=sqrt(1.0-(cos_theta*cos_theta));
-	theta=acos(cos_theta);
-	d_theta=(-1.0/sqrt(1.0-cos_theta*cos_theta))/(denom*denom);
-	d_theta1=2*denom-numer*2*d_ik/d_ij;
-	d_theta2=2*denom-numer*2*d_ij/d_ik;
-	d_theta1*=d_theta;
-	d_theta2*=d_theta;
+	/* cosine of theta by scalaproduct */
+	rijrik=v3_scalar_product(&dist_ij,&dist_ik);
+	dijdik=d_ij*d_ik;
+	cos_theta=rijrik/dijdik;
+
+	/* hack - cos theta machine accuracy problems! */
+	if(cos_theta>1.0||cos_theta<-1.0) {
+		printf("THETA CORRECTION\n");
+		moldyn->debug++;
+		if(fabs(cos_theta)>1.0+ACCEPTABLE_ERROR)
+			printf("[moldyn] WARNING: cos theta failure!\n");
+		if(cos_theta<0) {
+			cos_theta=-1.0;
+		}
+		else {
+			cos_theta=1.0;
+		}
+	}
+
+	d_costheta1=dijdik-rijrik*d_ik/d_ij;
+	d_costheta2=dijdik-rijrik*d_ij/d_ik;
 
 	h_cos=(h-cos_theta);
-	h_cos2=h_cos*h_cos;
-	d2_h_cos2=d2-h_cos2;
-
-	/* some usefull expressions */
-	frac1=c2/(d2-h_cos2);
-	bracket1=1+c2d2-frac1;
-	if(f_c_ik==0.0) {
-		bracket2=0.0;
-		bracket2_n_1=0.0;
-		bracket2_n=0.0;
-		bracket3=1.0;
-		printf("Foo -> 0: ");
-	}
-	else {
-		bracket2=f_c_ik*bracket1;
-		bracket2_n_1=pow(bracket2,n-1.0);
-		bracket2_n=bracket2_n_1*bracket2;
-		bracket3=1.0+betan*bracket2_n;
-		printf("Foo -> 1: ");
-	}
-	bracket3_pow_1=pow(bracket3,(-1.0/(2.0*n))-1.0);
-printf("THETA: %.15f %.15f\n",cos_theta,theta*180/(2*M_PI));
-	bracket3_pow=bracket3_pow_1*bracket3;
+	d2_h_cos2=d2+(h_cos*h_cos);
 
-	/* now go on with calc of b_ij and derivation of b_ij */
-	b_ij=chi*bracket3_pow;
+	frac=c2/(d2_h_cos2);
+	g=1.0+c2d2-frac;
 
-	/* derivation of theta */
-	v3_scale(&force,&dist_ij,d_theta1);
-	v3_scale(&temp,&dist_ik,d_theta2);
+	/* d_costheta contrib to db_ij (needed in all remaining cases) */
+	v3_scale(&temp,&dist_ij,d_costheta1);
+	v3_scale(&force,&dist_ik,d_costheta2);
 	v3_add(&force,&force,&temp);
+	v3_scale(&force,&force,-2.0*frac*h_cos/d2_h_cos2); /* f_c_ik missing */
 
-	/* part 1 of derivation of b_ij */
-	v3_scale(&force,&force,sin_theta*2*h_cos*f_c_ik*frac1);
+	if(d_ik<R) {
+		/* f_c_ik = 1, df_c_ik = 0 */	
+		/* => only d_costheta contrib to db_ij */
+		// => do nothing ...
 
-	/* part 2 of derivation of b_ij */
-	v3_scale(&temp,&dist_ik,df_c_ik*bracket1);
+		/* zeta, f_c_ik = 1 */
+		exchange->zeta+=g;
+	}
+	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));
 
-	/* sum up and scale ... */
-	v3_add(&temp,&temp,&force);
-	scale=bracket2_n_1*n*betan*(1+betan*bracket3_pow_1)*chi*(1.0/(2.0*n));
-	v3_scale(&temp,&temp,scale);
+		/* scale d_costheta contrib with f_c_ik */
+		v3_scale(&force,&force,f_c_ik);
 
-	/* now construct an energy and a force out of that */
-	v3_scale(&temp,&temp,f_a);
-	v3_scale(&force,&dist_ij,df_a*b_ij);
-	v3_add(&temp,&temp,&force);
-	v3_scale(&temp,&temp,f_c);
-	v3_scale(&force,&dist_ij,df_c*b_ij*f_a);
-	v3_add(&force,&force,&temp);
+		/* df_c_ik contrib to db_ij */
+		v3_scale(&temp,&dist_ik,df_c_ik*g);
 
-	/* add forces */
-	v3_add(&(ai->f),&(ai->f),&force);
-	/* energy is 0.5 f_r f_c */
-	moldyn->energy+=(0.5*f_a*b_ij*f_c);
+		/* sum up both parts */
+		v3_add(&force,&force,&temp);
+		
+		/* zeta */
+		exchange->zeta+=f_c_ik*g;
+	}
+printf("%.30f\n",exchange->zeta);
+	
+	/* add to db_ij */
+	v3_add(&(exchange->db_ij),&(exchange->db_ij),&force);
 				
 	return 0;
 }