X-Git-Url: https://www.hackdaworld.org/gitweb/?a=blobdiff_plain;f=moldyn.c;h=505f4960a18037b6d043ddf0d7596625660b328a;hb=7aface2e184e527132819f17b0fa18a6e1ba4bc3;hp=e96cdd4bd66e32632087321d07d12173024bec24;hpb=b040d775deb32173e6536464a3e2ad95a6a5bd55;p=physik%2Fposic.git

diff --git a/moldyn.c b/moldyn.c
index e96cdd4..505f496 100644
--- a/moldyn.c
+++ b/moldyn.c
@@ -5,29 +5,195 @@
  *
  */
 
-#include "moldyn.h"
-
+#define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <math.h>
+
+#include "moldyn.h"
 
 #include "math/math.h"
 #include "init/init.h"
+#include "random/random.h"
+#include "visual/visual.h"
+#include "list/list.h"
+
+
+int moldyn_init(t_moldyn *moldyn,int argc,char **argv) {
+
+	//int ret;
+
+	//ret=moldyn_parse_argv(moldyn,argc,argv);
+	//if(ret<0) return ret;
+
+	memset(moldyn,0,sizeof(t_moldyn));
+
+	rand_init(&(moldyn->random),NULL,1);
+	moldyn->random.status|=RAND_STAT_VERBOSE;
+
+	return 0;
+}
+
+int moldyn_shutdown(t_moldyn *moldyn) {
+
+	link_cell_shutdown(moldyn);
+	moldyn_log_shutdown(moldyn);
+	rand_close(&(moldyn->random));
+	free(moldyn->atom);
+
+	return 0;
+}
+
+int set_int_alg(t_moldyn *moldyn,u8 algo) {
+
+	switch(algo) {
+		case MOLDYN_INTEGRATE_VERLET:
+			moldyn->integrate=velocity_verlet;
+			break;
+		default:
+			printf("unknown integration algorithm: %02x\n",algo);
+			return -1;
+	}
+
+	return 0;
+}
+
+int set_cutoff(t_moldyn *moldyn,double cutoff) {
+
+	moldyn->cutoff=cutoff;
+
+	return 0;
+}
+
+int set_temperature(t_moldyn *moldyn,double t) {
+	
+	moldyn->t=t;
+
+	return 0;
+}
+
+int set_dim(t_moldyn *moldyn,double x,double y,double z,u8 visualize) {
+
+	moldyn->dim.x=x;
+	moldyn->dim.y=y;
+	moldyn->dim.z=z;
+
+	if(visualize) {
+		moldyn->vis.dim.x=x;
+		moldyn->vis.dim.y=y;
+		moldyn->vis.dim.z=z;
+	}
+
+	return 0;
+}
+
+int set_pbc(t_moldyn *moldyn,u8 x,u8 y,u8 z) {
+
+	if(x)
+		moldyn->status|=MOLDYN_STAT_PBX;
+
+	if(y)
+		moldyn->status|=MOLDYN_STAT_PBY;
+
+	if(z)
+		moldyn->status|=MOLDYN_STAT_PBZ;
+
+	return 0;
+}
+
+int set_potential1b(t_moldyn *moldyn,pf_func1b func,void *params) {
 
+	moldyn->func1b=func;
+	moldyn->pot1b_params=params;
 
-int create_lattice(unsigned char type,int element,double mass,double lc,
-                   int a,int b,int c,t_atom **atom) {
+	return 0;
+}
+
+int set_potential2b(t_moldyn *moldyn,pf_func2b func,void *params) {
+
+	moldyn->func2b=func;
+	moldyn->pot2b_params=params;
+
+	return 0;
+}
+
+int set_potential3b(t_moldyn *moldyn,pf_func3b func,void *params) {
+
+	moldyn->func3b=func;
+	moldyn->pot3b_params=params;
+
+	return 0;
+}
+
+int moldyn_set_log(t_moldyn *moldyn,u8 type,char *fb,int timer) {
+
+	switch(type) {
+		case LOG_TOTAL_ENERGY:
+			moldyn->ewrite=timer;
+			moldyn->efd=open(fb,O_WRONLY|O_CREAT|O_TRUNC);
+			if(moldyn->efd<0) {
+				perror("[moldyn] efd open");
+				return moldyn->efd;
+			}
+			dprintf(moldyn->efd,"# total energy log file\n");
+			break;
+		case LOG_TOTAL_MOMENTUM:
+			moldyn->mwrite=timer;
+			moldyn->mfd=open(fb,O_WRONLY|O_CREAT|O_TRUNC);
+			if(moldyn->mfd<0) {
+				perror("[moldyn] mfd open");
+				return moldyn->mfd;
+			}
+			dprintf(moldyn->efd,"# total momentum log file\n");
+			break;
+		case SAVE_STEP:
+			moldyn->swrite=timer;
+			strncpy(moldyn->sfb,fb,63);
+			break;
+		case VISUAL_STEP:
+			moldyn->vwrite=timer;
+			strncpy(moldyn->vfb,fb,63);
+			visual_init(&(moldyn->vis),fb);
+			break;
+		default:
+			printf("unknown log mechanism: %02x\n",type);
+			return -1;
+	}
+
+	return 0;
+}
+
+int moldyn_log_shutdown(t_moldyn *moldyn) {
+
+	if(moldyn->efd) close(moldyn->efd);
+	if(moldyn->mfd) close(moldyn->mfd);
+	if(moldyn->visual) visual_tini(moldyn->visual);
+
+	return 0;
+}
+
+int create_lattice(t_moldyn *moldyn,u8 type,double lc,int element,double mass,
+                   u8 attr,u8 bnum,int a,int b,int c) {
 
 	int count;
 	int ret;
 	t_3dvec origin;
+	t_atom *atom;
 
 	count=a*b*c;
+	atom=moldyn->atom;
 
 	if(type==FCC) count*=4;
+
 	if(type==DIAMOND) count*=8;
 
-	*atom=malloc(count*sizeof(t_atom));
-	if(*atom==NULL) {
+	atom=malloc(count*sizeof(t_atom));
+	if(atom==NULL) {
 		perror("malloc (atoms)");
 		return -1;
 	}
@@ -36,10 +202,10 @@ int create_lattice(unsigned char type,int element,double mass,double lc,
 
 	switch(type) {
 		case FCC:
-			ret=fcc_init(a,b,c,lc,*atom,&origin);
+			ret=fcc_init(a,b,c,lc,atom,&origin);
 			break;
 		case DIAMOND:
-			ret=diamond_init(a,b,c,lc,*atom,&origin);
+			ret=diamond_init(a,b,c,lc,atom,&origin);
 			break;
 		default:
 			printf("unknown lattice type (%02x)\n",type);
@@ -54,47 +220,1019 @@ int create_lattice(unsigned char type,int element,double mass,double lc,
 		return -1;
 	}
 
+	moldyn->count=count;
+
 	while(count) {
-		(*atom)[count-1].element=element;
-		(*atom)[count-1].mass=mass;
+		atom[count-1].element=element;
+		atom[count-1].mass=mass;
+		atom[count-1].attr=attr;
+		atom[count-1].bnum=bnum;
 		count-=1;
 	}
 
 	return ret;
 }
 
-int thermal_init(t_atom *atom,int count,double t) {
+int add_atom(t_moldyn *moldyn,int element,double mass,u8 bnum,u8 attr,
+             t_3dvec *r,t_3dvec *v) {
+
+	t_atom *atom;
+	void *ptr;
+	int count;
+	
+	atom=moldyn->atom;
+	count=++(moldyn->count);
+
+	ptr=realloc(atom,count*sizeof(t_atom));
+	if(!ptr) {
+		perror("[moldyn] realloc (add atom)");
+		return -1;
+	}
+	moldyn->atom=ptr;
+
+	atom=moldyn->atom;
+	atom->r=*r;
+	atom->v=*v;
+	atom->element=element;
+	atom->bnum=bnum;
+	atom->attr=attr;
+
+	return 0;
+}
+
+int destroy_atoms(t_moldyn *moldyn) {
+
+	if(moldyn->atom) free(moldyn->atom);
+
+	return 0;
+}
+
+int thermal_init(t_moldyn *moldyn) {
 
 	/*
 	 * - gaussian distribution of velocities
+	 * - zero total momentum
 	 * - velocity scaling (E = 3/2 N k T), E: kinetic energy
 	 */
 
 	int i;
-	double e,c,v;
+	double v,sigma;
+	t_3dvec p_total,delta;
+	t_atom *atom;
+	t_random *random;
 
-	e=.0;
+	atom=moldyn->atom;
+	random=&(moldyn->random);
 
-	for(i=0;i<count;i++) {
+	/* gaussian distribution of velocities */
+	v3_zero(&p_total);
+	for(i=0;i<moldyn->count;i++) {
+		sigma=sqrt(2.0*K_BOLTZMANN*moldyn->t/atom[i].mass);
 		/* x direction */
-		v=gauss_rand();
-		atom[count].v.x=v;
-		e+=0.5*atom[count].mass*v*v;
+		v=sigma*rand_get_gauss(random);
+		atom[i].v.x=v;
+		p_total.x+=atom[i].mass*v;
 		/* y direction */
-		v=gauss_rand();
-		atom[count].v.y=v;
-		e+=0.5*atom[count].mass*v*v;
+		v=sigma*rand_get_gauss(random);
+		atom[i].v.y=v;
+		p_total.y+=atom[i].mass*v;
 		/* z direction */
-		v=gauss_rand();
-		atom[count].v.z=v;
-		e+=0.5*atom[count].mass*v*v;
+		v=sigma*rand_get_gauss(random);
+		atom[i].v.z=v;
+		p_total.z+=atom[i].mass*v;
+	}
+
+	/* zero total momentum */
+	v3_scale(&p_total,&p_total,1.0/moldyn->count);
+	for(i=0;i<moldyn->count;i++) {
+		v3_scale(&delta,&p_total,1.0/atom[i].mass);
+		v3_sub(&(atom[i].v),&(atom[i].v),&delta);
+	}
+
+	/* velocity scaling */
+	scale_velocity(moldyn);
+
+	return 0;
+}
+
+int scale_velocity(t_moldyn *moldyn) {
+
+	int i;
+	double e,c;
+	t_atom *atom;
+
+	atom=moldyn->atom;
+
+	/*
+	 * - velocity scaling (E = 3/2 N k T), E: kinetic energy
+	 */
+	e=0.0;
+	for(i=0;i<moldyn->count;i++)
+		e+=0.5*atom[i].mass*v3_absolute_square(&(atom[i].v));
+	c=sqrt((2.0*e)/(3.0*moldyn->count*K_BOLTZMANN*moldyn->t));
+	for(i=0;i<moldyn->count;i++)
+		v3_scale(&(atom[i].v),&(atom[i].v),(1.0/c));
+
+	return 0;
+}
+
+double get_e_kin(t_moldyn *moldyn) {
+
+	int i;
+	t_atom *atom;
+
+	atom=moldyn->atom;
+	moldyn->ekin=0.0;
+
+	for(i=0;i<moldyn->count;i++)
+		moldyn->ekin+=0.5*atom[i].mass*v3_absolute_square(&(atom[i].v));
+
+	return moldyn->ekin;
+}
+
+double get_e_pot(t_moldyn *moldyn) {
+
+	return moldyn->energy;
+}
+
+double update_e_kin(t_moldyn *moldyn) {
+
+	return(get_e_kin(moldyn));
+}
+
+double get_total_energy(t_moldyn *moldyn) {
+
+	return(moldyn->ekin+moldyn->energy);
+}
+
+t_3dvec get_total_p(t_moldyn *moldyn) {
+
+	t_3dvec p,p_total;
+	int i;
+	t_atom *atom;
+
+	atom=moldyn->atom;
+
+	v3_zero(&p_total);
+	for(i=0;i<moldyn->count;i++) {
+		v3_scale(&p,&(atom[i].v),atom[i].mass);
+		v3_add(&p_total,&p_total,&p);
+	}
+
+	return p_total;
+}
+
+double estimate_time_step(t_moldyn *moldyn,double nn_dist,double t) {
+
+	double tau;
+
+	tau=0.05*nn_dist/(sqrt(3.0*K_BOLTZMANN*t/moldyn->atom[0].mass));
+	tau*=1.0E-9;
+	if(tau<moldyn->tau)
+		printf("[moldyn] warning: time step  (%f > %.15f)\n",
+		       moldyn->tau,tau);
+
+	return tau;	
+}
+
+/*
+ * numerical tricks
+ */
+
+/* linked list / cell method */
+
+int link_cell_init(t_moldyn *moldyn) {
+
+	t_linkcell *lc;
+	int i;
+	int fd;
+
+	fd=open("/dev/null",O_WRONLY);
+
+	lc=&(moldyn->lc);
+
+	/* partitioning the md cell */
+	lc->nx=moldyn->dim.x/moldyn->cutoff;
+	lc->x=moldyn->dim.x/lc->nx;
+	lc->ny=moldyn->dim.y/moldyn->cutoff;
+	lc->y=moldyn->dim.y/lc->ny;
+	lc->nz=moldyn->dim.z/moldyn->cutoff;
+	lc->z=moldyn->dim.z/lc->nz;
+
+	lc->cells=lc->nx*lc->ny*lc->nz;
+	lc->subcell=malloc(lc->cells*sizeof(t_list));
+
+	printf("[moldyn] initializing linked cells (%d)\n",lc->cells);
+
+	for(i=0;i<lc->cells;i++)
+		//list_init(&(lc->subcell[i]),1);
+		list_init(&(lc->subcell[i]),fd);
+
+ 	link_cell_update(moldyn);
+	
+	return 0;
+}
+
+int link_cell_update(t_moldyn *moldyn) {
+
+	int count,i,j,k;
+	int nx,ny,nz;
+	t_atom *atom;
+	t_linkcell *lc;
+
+	atom=moldyn->atom;
+	lc=&(moldyn->lc);
+
+	nx=lc->nx;
+	ny=lc->ny;
+	nz=lc->nz;
+
+	for(i=0;i<lc->cells;i++)
+		list_destroy(&(moldyn->lc.subcell[i]));
+	
+	for(count=0;count<moldyn->count;count++) {
+		i=(atom[count].r.x+(moldyn->dim.x/2))/lc->x;
+		j=(atom[count].r.y+(moldyn->dim.y/2))/lc->y;
+		k=(atom[count].r.z+(moldyn->dim.z/2))/lc->z;
+		list_add_immediate_ptr(&(moldyn->lc.subcell[i+j*nx+k*nx*ny]),
+		                       &(atom[count]));
 	}
 
-	c=sqrt((2.0*e)/(3.0*count*K_BOLTZMANN));
+	return 0;
+}
+
+int link_cell_neighbour_index(t_moldyn *moldyn,int i,int j,int k,t_list *cell) {
+
+	t_linkcell *lc;
+	int a;
+	int count1,count2;
+	int ci,cj,ck;
+	int nx,ny,nz;
+	int x,y,z;
+	u8 bx,by,bz;
+
+	lc=&(moldyn->lc);
+	nx=lc->nx;
+	ny=lc->ny;
+	nz=lc->nz;
+	count1=1;
+	count2=27;
+	a=nx*ny;
+
+
+	cell[0]=lc->subcell[i+j*nx+k*a];
+	for(ci=-1;ci<=1;ci++) {
+		bx=0;
+		x=i+ci;
+		if((x<0)||(x>=nx)) {
+			x=(x+nx)%nx;
+			bx=1;
+		}
+		for(cj=-1;cj<=1;cj++) {
+			by=0;
+			y=j+cj;
+			if((y<0)||(y>=ny)) {
+				y=(y+ny)%ny;
+				by=1;
+			}
+			for(ck=-1;ck<=1;ck++) {
+				bz=0;
+				z=k+ck;
+				if((z<0)||(z>=nz)) {
+					z=(z+nz)%nz;
+					bz=1;
+				}
+				if(!(ci|cj|ck)) continue;
+				if(bx|by|bz) {
+					cell[--count2]=lc->subcell[x+y*nx+z*a];
+				}
+				else {
+					cell[count1++]=lc->subcell[x+y*nx+z*a];
+				}
+			}
+		}
+	}
+
+	lc->dnlc=count2;
+	lc->countn=27;
+
+	return count2;
+}
+
+int link_cell_shutdown(t_moldyn *moldyn) {
+
+	int i;
+	t_linkcell *lc;
+
+	lc=&(moldyn->lc);
+
+	for(i=0;i<lc->nx*lc->ny*lc->nz;i++)
+		list_shutdown(&(moldyn->lc.subcell[i]));
+
+	return 0;
+}
+
+int moldyn_add_schedule(t_moldyn *moldyn,int runs,double tau) {
+
+	int count;
+	void *ptr;
+	t_moldyn_schedule *schedule;
+
+	schedule=&(moldyn->schedule);
+	count=++(schedule->content_count);
+
+	ptr=realloc(moldyn->schedule.runs,count*sizeof(int));
+	if(!ptr) {
+		perror("[moldyn] realloc (runs)");
+		return -1;
+	}
+	moldyn->schedule.runs=ptr;
+	moldyn->schedule.runs[count-1]=runs;
+
+	ptr=realloc(schedule->tau,count*sizeof(double));
+	if(!ptr) {
+		perror("[moldyn] realloc (tau)");
+		return -1;
+	}
+	moldyn->schedule.tau=ptr;
+	moldyn->schedule.tau[count-1]=tau;
+
+	return 0;
+}
+
+int moldyn_set_schedule_hook(t_moldyn *moldyn,void *hook,void *hook_params) {
+
+	moldyn->schedule.hook=hook;
+	moldyn->schedule.hook_params=hook_params;
+	
+	return 0;
+}
+
+/*
+ *
+ * 'integration of newtons equation' - algorithms
+ *
+ */
+
+/* start the integration */
+
+int moldyn_integrate(t_moldyn *moldyn) {
+
+	int i,sched;
+	unsigned int e,m,s,v;
+	t_3dvec p;
+	t_moldyn_schedule *schedule;
+
+	int fd;
+	char fb[128];
+
+	schedule=&(moldyn->schedule);
+
+	/* initialize linked cell method */
+	link_cell_init(moldyn);
+
+	/* logging & visualization */
+	e=moldyn->ewrite;
+	m=moldyn->mwrite;
+	s=moldyn->swrite;
+	v=moldyn->vwrite;
+
+	/* 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);
+
+	/* zero absolute time */
+	moldyn->time=0.0;
+
+	for(sched=0;sched<moldyn->schedule.content_count;sched++) {
+
+		/* setting amount of runs and finite time step size */
+		moldyn->tau=schedule->tau[sched];
+		moldyn->tau_square=moldyn->tau*moldyn->tau;
+		moldyn->time_steps=schedule->runs[sched];
+
+	/* integration according to schedule */
+
+	for(i=0;i<moldyn->time_steps;i++) {
+
+		/* integration step */
+		moldyn->integrate(moldyn);
+
+		/* increase absolute time */
+		moldyn->time+=moldyn->tau;
+
+		/* check for log & visualization */
+		if(e) {
+			if(!(i%e))
+				dprintf(moldyn->efd,
+				        "%.15f %.45f %.45f %.45f\n",
+				        moldyn->time,update_e_kin(moldyn),
+				        moldyn->energy,
+				        get_total_energy(moldyn));
+		}
+		if(m) {
+			if(!(i%m)) {
+				p=get_total_p(moldyn);
+				dprintf(moldyn->mfd,
+				        "%.15f %.45f\n",moldyn->time,
+				        v3_norm(&p));
+			}
+		}
+		if(s) {
+			if(!(i%s)) {
+				snprintf(fb,128,"%s-%f-%.15f.save",moldyn->sfb,
+				         moldyn->t,i*moldyn->tau);
+				fd=open(fb,O_WRONLY|O_TRUNC|O_CREAT);
+				if(fd<0) perror("[moldyn] save fd open");
+				else {
+					write(fd,moldyn,sizeof(t_moldyn));
+					write(fd,moldyn->atom,
+					      moldyn->count*sizeof(t_atom));
+				}
+				close(fd);
+			}	
+		}
+		if(v) {
+			if(!(i%v)) {
+				visual_atoms(&(moldyn->vis),moldyn->time,
+				             moldyn->atom,moldyn->count);
+				printf("\rsched: %d, steps: %d",sched,i);
+				fflush(stdout);
+			}
+		}
+
+	}
+
+		/* check for hooks */
+		if(schedule->hook)
+			schedule->hook(moldyn,schedule->hook_params);
+
+	}
+
+	return 0;
+}
+
+/* velocity verlet */
+
+int velocity_verlet(t_moldyn *moldyn) {
+
+	int i,count;
+	double tau,tau_square;
+	t_3dvec delta;
+	t_atom *atom;
+
+	atom=moldyn->atom;
+	count=moldyn->count;
+	tau=moldyn->tau;
+	tau_square=moldyn->tau_square;
+
+	for(i=0;i<count;i++) {
+		/* new positions */
+		v3_scale(&delta,&(atom[i].v),tau);
+		v3_add(&(atom[i].r),&(atom[i].r),&delta);
+		v3_scale(&delta,&(atom[i].f),0.5*tau_square/atom[i].mass);
+		v3_add(&(atom[i].r),&(atom[i].r),&delta);
+		v3_per_bound(&(atom[i].r),&(moldyn->dim));
+
+		/* velocities */
+		v3_scale(&delta,&(atom[i].f),0.5*tau/atom[i].mass);
+		v3_add(&(atom[i].v),&(atom[i].v),&delta);
+	}
+
+	/* neighbour list update */
+	link_cell_update(moldyn);
+
+	/* forces depending on chosen potential */
+	potential_force_calc(moldyn);
+	//moldyn->potential_force_function(moldyn);
+
+	for(i=0;i<count;i++) {
+		/* again velocities */
+		v3_scale(&delta,&(atom[i].f),0.5*tau/atom[i].mass);
+		v3_add(&(atom[i].v),&(atom[i].v),&delta);
+	}
+
+	return 0;
+}
+
+
+/*
+ *
+ * potentials & corresponding forces
+ * 
+ */
+
+/* generic potential and force calculation */
+
+int potential_force_calc(t_moldyn *moldyn) {
+
+	int i,j,k,count;
+	t_atom *atom,*btom,*ktom;
+	t_linkcell *lc;
+	t_list neighbour[27];
+	t_list *this,*thisk,*neighbourk;
+	u8 bc,bck;
+	int countn,dnlc;
+
+	count=moldyn->count;
+	atom=moldyn->atom;
+	lc=&(moldyn->lc);
+
+	/* reset energy */
+	moldyn->energy=0.0;
+
+	for(i=0;i<count;i++) {
+	
+		/* reset force */
+		v3_zero(&(atom[i].f));
+
+		/* single particle potential/force */
+		if(atom[i].attr&ATOM_ATTR_1BP)
+			moldyn->func1b(moldyn,&(atom[i]));
+
+		/* 2 body pair potential/force */
+		if(atom[i].attr&(ATOM_ATTR_2BP|ATOM_ATTR_3BP)) {
+		
+			link_cell_neighbour_index(moldyn,
+				(atom[i].r.x+moldyn->dim.x/2)/lc->x,
+				(atom[i].r.y+moldyn->dim.y/2)/lc->y,
+				(atom[i].r.z+moldyn->dim.z/2)/lc->z,
+				neighbour);
+
+			countn=lc->countn;
+			dnlc=lc->dnlc;
+
+			for(j=0;j<countn;j++) {
+
+				this=&(neighbour[j]);
+				list_reset(this);
+
+				if(this->start==NULL)
+					continue;
+
+				bc=(j<dnlc)?0:1;
+
+				do {
+					btom=this->current->data;
+
+					if(btom==&(atom[i]))
+						continue;
+
+					if((btom->attr&ATOM_ATTR_2BP)&
+					   (atom[i].attr&ATOM_ATTR_2BP))
+						moldyn->func2b(moldyn,
+						               &(atom[i]),
+						               btom,
+						               bc);
+
+					/* 3 body potential/force */
+
+					if(!(atom[i].attr&ATOM_ATTR_3BP)||
+					   !(btom->attr&ATOM_ATTR_3BP))
+						continue;
+
+					link_cell_neighbour_index(moldyn,
+					   (btom->r.x+moldyn->dim.x/2)/lc->x,
+					   (btom->r.y+moldyn->dim.y/2)/lc->y,
+					   (btom->r.z+moldyn->dim.z/2)/lc->z,
+					   neighbourk);
+
+					for(k=0;k<lc->countn;k++) {
+
+						thisk=&(neighbourk[k]);
+						list_reset(thisk);
+					
+						if(thisk->start==NULL)
+							continue;
+
+						bck=(k<lc->dnlc)?0:1;
+
+						do {
+
+			ktom=thisk->current->data;
+
+			if(!(ktom->attr&ATOM_ATTR_3BP))
+				continue;
+
+			if(ktom==btom)
+				continue;
+
+			if(ktom==&(atom[i]))
+				continue;
+
+			moldyn->func3b(moldyn,&(atom[i]),btom,ktom,bck);
+
+						} while(list_next(thisk)!=\
+						        L_NO_NEXT_ELEMENT);
+
+					}
+					
+				} while(list_next(this)!=L_NO_NEXT_ELEMENT);
+			}
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * periodic boundayr checking
+ */
+
+int check_per_bound(t_moldyn *moldyn,t_3dvec *a) {
+	
+	double x,y,z;
+	t_3dvec *dim;
+
+	dim=&(moldyn->dim);
+
+	x=0.5*dim->x;
+	y=0.5*dim->y;
+	z=0.5*dim->z;
+
+	if(moldyn->status&MOLDYN_STAT_PBX) {
+		if(a->x>=x) a->x-=dim->x;
+		else if(-a->x>x) a->x+=dim->x;
+	}
+	if(moldyn->status&MOLDYN_STAT_PBY) {
+		if(a->y>=y) a->y-=dim->y;
+		else if(-a->y>y) a->y+=dim->y;
+	}
+	if(moldyn->status&MOLDYN_STAT_PBZ) {
+		if(a->z>=z) a->z-=dim->z;
+		else if(-a->z>z) a->z+=dim->z;
+	}
+
+	return 0;
+}
+        
+
+/*
+ * example potentials
+ */
+
+/* harmonic oscillator potential and force */
+
+int harmonic_oscillator(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
+
+	t_ho_params *params;
+	t_3dvec force,distance;
+	double d;
+	double sc,equi_dist;
+
+	params=moldyn->pot2b_params;
+	sc=params->spring_constant;
+	equi_dist=params->equilibrium_distance;
+
+	v3_sub(&distance,&(ai->r),&(aj->r));
+	
+	v3_per_bound(&distance,&(moldyn->dim));
+	if(bc) check_per_bound(moldyn,&distance);
+	d=v3_norm(&distance);
+	if(d<=moldyn->cutoff) {
+		/* energy is 1/2 (d-d0)^2, but we will add this twice ... */
+		moldyn->energy+=(0.25*sc*(d-equi_dist)*(d-equi_dist));
+		v3_scale(&force,&distance,-sc*(1.0-(equi_dist/d)));
+		v3_add(&(ai->f),&(ai->f),&force);
+	}
+
+	return 0;
+}
+
+/* lennard jones potential & force for one sort of atoms */
+ 
+int lennard_jones(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
+
+	t_lj_params *params;
+	t_3dvec force,distance;
+	double d,h1,h2;
+	double eps,sig6,sig12;
+
+	params=moldyn->pot2b_params;
+	eps=params->epsilon4;
+	sig6=params->sigma6;
+	sig12=params->sigma12;
+
+	v3_sub(&distance,&(ai->r),&(aj->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,d);
+		v3_add(&(ai->f),&(aj->f),&force);
+	}
+
+	return 0;
+}
+
+/*
+ * tersoff potential & force for 2 sorts of atoms
+ */
+
+/* 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->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);
+
+	/* save for use in 3bp */ /* REALLY ?!?!?! */
+	exchange->dist_ij=dist_ij;
+
+	/* constants */
+	if(num==aj->bnum) {
+		S=params->S[num];
+		R=params->R[num];
+		A=params->A[num];
+		lambda=params->lambda[num];
+		/* more constants depending of atoms i and j, needed in 3bp */
+		params->exchange.B=&(params->B[num]);
+		params->exchange.mu=&(params->mu[num]);
+		mu=params->mu[num];
+		params->exchange.chi=1.0;
+	}
+	else {
+		S=params->Smixed;
+		R=params->Rmixed;
+		A=params->Amixed;
+		lambda=params->lambda_m;
+		/* more constants depending of atoms i and j, needed in 3bp */
+		params->exchange.B=&(params->Bmixed);
+		params->exchange.mu=&(params->mu_m);
+		mu=params->mu_m;
+		params->exchange.chi=params->chi;
+	}
+
+	d_ij=v3_norm(&dist_ij);
+
+	/* save for use in 3bp */
+	exchange->d_ij=d_ij;
+
+	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, but we will sum it up twice ... */
+	moldyn->energy+=(0.25*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;
+
+	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,b_ij,f_a,df_a;
+	double f_c_ik,df_c_ik,arg;
+	double scale;
+	double chi;
+	double n,c,d,h,beta,betan;
+	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;
+	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;
+
+	f_a=params->exchange.f_a;
+	df_a=params->exchange.df_a;
+	
+	/* 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;
+	}
+
+	/* calc of f_c_ik */
+	if(d_ik>S)
+		return 0;
+
+	if(d_ik<R) {
+		/* f_c_ik = 1, df_c_ik = 0 */
+		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);
+
+	beta=*(exchange->beta);
+	betan=exchange->betan;
+	n=*(exchange->n);
+	c=*(exchange->c);
+	d=*(exchange->d);
+	h=*(exchange->h);
+	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;
+	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;
+
+	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;
+	bracket2=f_c_ik*bracket1;
+	bracket2_n_1=pow(bracket2,n-1.0);
+	bracket2_n=bracket2_n_1*bracket2;
+	bracket3=1+betan*bracket2_n;
+	bracket3_pow_1=pow(bracket3,(-1.0/(2.0*n))-1.0);
+	bracket3_pow=bracket3_pow_1*bracket3;
+
+	/* now go on with calc of b_ij and derivation of b_ij */
+	b_ij=chi*bracket3_pow;
+
+	/* derivation of theta */
+	v3_scale(&force,&dist_ij,d_theta1);
+	v3_scale(&temp,&dist_ik,d_theta2);
+	v3_add(&force,&force,&temp);
+
+	/* part 1 of derivation of b_ij */
+	v3_scale(&force,&force,sin_theta*2*h_cos*f_c_ik*frac1);
+
+	/* part 2 of derivation of b_ij */
+	v3_scale(&temp,&dist_ik,df_c_ik*bracket1);
+
+	/* 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);
 
-	for(i=0;i<count;i++)
-		v3_scale(&(atom[count].v),&(atom[count].v),(1.0/c));
+	/* 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);
 
+	/* add forces */
+	v3_add(&(ai->f),&(ai->f),&force);
+	/* energy is 0.5 f_r f_c, but we will sum it up twice ... */
+	moldyn->energy+=(0.25*f_a*b_ij*f_c);
+				
 	return 0;
 }