X-Git-Url: https://www.hackdaworld.org/gitweb/?a=blobdiff_plain;f=moldyn.c;h=505f4960a18037b6d043ddf0d7596625660b328a;hb=7aface2e184e527132819f17b0fa18a6e1ba4bc3;hp=57f76c433ae7d431fc860dc51ddc21b6982a6d29;hpb=06912ca45b46de412570a4bd5b5484aa9e8d6e6b;p=physik%2Fposic.git

diff --git a/moldyn.c b/moldyn.c
index 57f76c4..505f496 100644
--- a/moldyn.c
+++ b/moldyn.c
@@ -23,229 +23,177 @@
 #include "visual/visual.h"
 #include "list/list.h"
 
-int moldyn_usage(char **argv) {
-
-	printf("\n%s usage:\n\n",argv[0]);
-	printf("--- general options ---\n");
-	printf("-E <steps> <file> (log total energy)\n");
-	printf("-M <steps> <file> (log total momentum)\n");
-	printf("-D <steps> <file> (dump total information)\n");
-	printf("-S <steps> <filebase> (single save file)\n");
-	printf("-V <steps> <filebase> (rasmol file)\n");
-	printf("--- physics options ---\n");
-	printf("-T <temperature> [K] (%f)\n",MOLDYN_TEMP);
-	printf("-t <timestep tau> [s] (%.15f)\n",MOLDYN_TAU);
-	printf("-C <cutoff radius> [m] (%.15f)\n",MOLDYN_CUTOFF);
-	printf("-R <runs> (%d)\n",MOLDYN_RUNS);
-	printf(" -- integration algo --\n");
-	printf("  -I <number> (%d)\n",MOLDYN_INTEGRATE_DEFAULT);
-	printf("     0: velocity verlet\n");
-	printf(" -- potential --\n");
-	printf("  -P <number> <param1 param2 ...>\n");
-	printf("     0: harmonic oscillator\n");
-	printf("        param1: spring constant\n");
-	printf("        param2: equilibrium distance\n");
-	printf("     1: lennard jones\n");
-	printf("        param1: epsilon\n");
-	printf("        param2: sigma\n");
-	printf("\n");
+
+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_parse_argv(t_moldyn *moldyn,int argc,char **argv) {
+int moldyn_shutdown(t_moldyn *moldyn) {
 
-	int i;
-	t_ho_params hop;
-	t_lj_params ljp;
-	t_tersoff_params tp;
-	double s,e;
+	link_cell_shutdown(moldyn);
+	moldyn_log_shutdown(moldyn);
+	rand_close(&(moldyn->random));
+	free(moldyn->atom);
 
-	memset(moldyn,0,sizeof(t_moldyn));
+	return 0;
+}
 
-	/* default values */
-	moldyn->t=MOLDYN_TEMP;
-	moldyn->tau=MOLDYN_TAU;
-	moldyn->time_steps=MOLDYN_RUNS;
-	moldyn->integrate=velocity_verlet;
-	moldyn->potential_force_function=lennard_jones;
-
-	/* parse argv */
-	for(i=1;i<argc;i++) {
-		if(argv[i][0]=='-') {
-			switch(argv[i][1]){
-				case 'E':
-					moldyn->ewrite=atoi(argv[++i]);
-					strncpy(moldyn->efb,argv[++i],64);
-					break;
-				case 'M':
-					moldyn->mwrite=atoi(argv[++i]);
-					strncpy(moldyn->mfb,argv[++i],64);
-					break;
-				case 'S':
-					moldyn->swrite=atoi(argv[++i]);
-					strncpy(moldyn->sfb,argv[++i],64);
-					break;
-				case 'V':
-					moldyn->vwrite=atoi(argv[++i]);
-					strncpy(moldyn->vfb,argv[++i],64);
-					break;
-				case 'T':
-					moldyn->t=atof(argv[++i]);
-					break;
-				case 't':
-					moldyn->tau=atof(argv[++i]);
-					break;
-				case 'C':
-					moldyn->cutoff=atof(argv[++i]);
-					break;
-				case 'R':
-					moldyn->time_steps=atoi(argv[++i]);
-					break;
-				case 'I':
-	/* integration algorithm */
-	switch(atoi(argv[++i])) {
+int set_int_alg(t_moldyn *moldyn,u8 algo) {
+
+	switch(algo) {
 		case MOLDYN_INTEGRATE_VERLET:
 			moldyn->integrate=velocity_verlet;
 			break;
 		default:
-			printf("unknown integration algo %s\n",argv[i]);
-			moldyn_usage(argv);
+			printf("unknown integration algorithm: %02x\n",algo);
 			return -1;
 	}
 
-				case 'P':
-	/* potential + params */
-	switch(atoi(argv[++i])) {
-		case MOLDYN_POTENTIAL_HO:
-			hop.spring_constant=atof(argv[++i]);
-			hop.equilibrium_distance=atof(argv[++i]);
-			moldyn->pot_params=malloc(sizeof(t_ho_params));
-			memcpy(moldyn->pot_params,&hop,sizeof(t_ho_params));
-			moldyn->potential_force_function=harmonic_oscillator;
-			break;
-		case MOLDYN_POTENTIAL_LJ:
-			e=atof(argv[++i]);
-			s=atof(argv[++i]);
-			ljp.epsilon4=4*e;
-			ljp.sigma6=s*s*s*s*s*s;
-			ljp.sigma12=ljp.sigma6*ljp.sigma6;
-			moldyn->pot_params=malloc(sizeof(t_lj_params));
-			memcpy(moldyn->pot_params,&ljp,sizeof(t_lj_params));
-			moldyn->potential_force_function=lennard_jones;
-			break;
-		default:
-			printf("unknown potential %s\n",argv[i]);
-			moldyn_usage(argv);
-			return -1;
-	}
+	return 0;
+}
 
-				default:
-					printf("unknown option %s\n",argv[i]);
-					moldyn_usage(argv);
-					return -1;
-			}
-		} else {
-			moldyn_usage(argv);
-			return -1;
-		}
-	}
+int set_cutoff(t_moldyn *moldyn,double cutoff) {
+
+	moldyn->cutoff=cutoff;
 
 	return 0;
 }
 
-int moldyn_log_init(t_moldyn *moldyn) {
+int set_temperature(t_moldyn *moldyn,double t) {
+	
+	moldyn->t=t;
+
+	return 0;
+}
 
-	moldyn->lvstat=0;
-	t_visual *vis;
+int set_dim(t_moldyn *moldyn,double x,double y,double z,u8 visualize) {
 
-	vis=&(moldyn->vis);
+	moldyn->dim.x=x;
+	moldyn->dim.y=y;
+	moldyn->dim.z=z;
 
-	if(moldyn->ewrite) {
-		moldyn->efd=open(moldyn->efb,O_WRONLY|O_CREAT|O_TRUNC);
-		if(moldyn->efd<0) {
-			perror("[moldyn] efd open");
-			return moldyn->efd;
-		}
-		dprintf(moldyn->efd,"# moldyn total energy logfile\n");
-		moldyn->lvstat|=MOLDYN_LVSTAT_TOTAL_E;
+	if(visualize) {
+		moldyn->vis.dim.x=x;
+		moldyn->vis.dim.y=y;
+		moldyn->vis.dim.z=z;
 	}
 
-	if(moldyn->mwrite) {
-		moldyn->mfd=open(moldyn->mfb,O_WRONLY|O_CREAT|O_TRUNC);
-		if(moldyn->mfd<0) {
-			perror("[moldyn] mfd open");
-			return moldyn->mfd;
-		}
-		dprintf(moldyn->mfd,"# moldyn total momentum logfile\n");
-		moldyn->lvstat|=MOLDYN_LVSTAT_TOTAL_M;
-	}
+	return 0;
+}
 
-	if(moldyn->swrite)
-		moldyn->lvstat|=MOLDYN_LVSTAT_SAVE;
+int set_pbc(t_moldyn *moldyn,u8 x,u8 y,u8 z) {
 
-	if((moldyn->vwrite)&&(vis)) {
-		moldyn->visual=vis;
-		visual_init(vis,moldyn->vfb);
-		moldyn->lvstat|=MOLDYN_LVSTAT_VISUAL;
-	}
+	if(x)
+		moldyn->status|=MOLDYN_STAT_PBX;
+
+	if(y)
+		moldyn->status|=MOLDYN_STAT_PBY;
 
-	moldyn->lvstat|=MOLDYN_LVSTAT_INITIALIZED;
+	if(z)
+		moldyn->status|=MOLDYN_STAT_PBZ;
 
 	return 0;
 }
 
-int moldyn_log_shutdown(t_moldyn *moldyn) {
+int set_potential1b(t_moldyn *moldyn,pf_func1b func,void *params) {
 
-	if(moldyn->efd) close(moldyn->efd);
-	if(moldyn->mfd) close(moldyn->efd);
-	if(moldyn->dfd) close(moldyn->efd);
-	if(moldyn->visual) visual_tini(moldyn->visual);
+	moldyn->func1b=func;
+	moldyn->pot1b_params=params;
 
 	return 0;
 }
 
-int moldyn_init(t_moldyn *moldyn,int argc,char **argv) {
+int set_potential2b(t_moldyn *moldyn,pf_func2b func,void *params) {
 
-	int ret;
+	moldyn->func2b=func;
+	moldyn->pot2b_params=params;
 
-	ret=moldyn_parse_argv(moldyn,argc,argv);
-	if(ret<0) return ret;
+	return 0;
+}
 
-	ret=moldyn_log_init(moldyn);
-	if(ret<0) return ret;
+int set_potential3b(t_moldyn *moldyn,pf_func3b func,void *params) {
 
-	rand_init(&(moldyn->random),NULL,1);
-	moldyn->random.status|=RAND_STAT_VERBOSE;
+	moldyn->func3b=func;
+	moldyn->pot3b_params=params;
 
-	moldyn->status=0;
+	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_shutdown(t_moldyn *moldyn) {
+int moldyn_log_shutdown(t_moldyn *moldyn) {
 
-	moldyn_log_shutdown(moldyn);
-	rand_close(&(moldyn->random));
-	free(moldyn->atom);
+	if(moldyn->efd) close(moldyn->efd);
+	if(moldyn->mfd) close(moldyn->mfd);
+	if(moldyn->visual) visual_tini(moldyn->visual);
 
 	return 0;
 }
 
-int create_lattice(unsigned char type,int element,double mass,double lc,
-                   int a,int b,int c,t_atom **atom) {
+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;
 	}
@@ -254,10 +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);
@@ -272,18 +220,49 @@ 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 destroy_lattice(t_atom *atom) {
+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(atom) free(atom);
+	if(moldyn->atom) free(moldyn->atom);
 
 	return 0;
 }
@@ -357,18 +336,18 @@ int scale_velocity(t_moldyn *moldyn) {
 	return 0;
 }
 
-double get_e_kin(t_atom *atom,int count) {
+double get_e_kin(t_moldyn *moldyn) {
 
 	int i;
-	double e;
+	t_atom *atom;
 
-	e=0.0;
+	atom=moldyn->atom;
+	moldyn->ekin=0.0;
 
-	for(i=0;i<count;i++) {
-		e+=0.5*atom[i].mass*v3_absolute_square(&(atom[i].v));
-	}
+	for(i=0;i<moldyn->count;i++)
+		moldyn->ekin+=0.5*atom[i].mass*v3_absolute_square(&(atom[i].v));
 
-	return e;
+	return moldyn->ekin;
 }
 
 double get_e_pot(t_moldyn *moldyn) {
@@ -376,23 +355,26 @@ double get_e_pot(t_moldyn *moldyn) {
 	return moldyn->energy;
 }
 
-double get_total_energy(t_moldyn *moldyn) {
+double update_e_kin(t_moldyn *moldyn) {
 
-	double e;
+	return(get_e_kin(moldyn));
+}
 
-	e=get_e_kin(moldyn->atom,moldyn->count);
-	e+=get_e_pot(moldyn);
+double get_total_energy(t_moldyn *moldyn) {
 
-	return e;
+	return(moldyn->ekin+moldyn->energy);
 }
 
-t_3dvec get_total_p(t_atom *atom, int count) {
+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<count;i++) {
+	for(i=0;i<moldyn->count;i++) {
 		v3_scale(&p,&(atom[i].v),atom[i].mass);
 		v3_add(&p_total,&p_total,&p);
 	}
@@ -423,11 +405,11 @@ int link_cell_init(t_moldyn *moldyn) {
 
 	t_linkcell *lc;
 	int i;
+	int fd;
 
-	lc=&(moldyn->lc);
+	fd=open("/dev/null",O_WRONLY);
 
-	/* list log fd */
-	lc->listfd=open("/dev/null",O_WRONLY);
+	lc=&(moldyn->lc);
 
 	/* partitioning the md cell */
 	lc->nx=moldyn->dim.x/moldyn->cutoff;
@@ -440,11 +422,11 @@ int link_cell_init(t_moldyn *moldyn) {
 	lc->cells=lc->nx*lc->ny*lc->nz;
 	lc->subcell=malloc(lc->cells*sizeof(t_list));
 
-	printf("initializing linked cells (%d)\n",lc->cells);
+	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]));
+		list_init(&(lc->subcell[i]),fd);
 
  	link_cell_update(moldyn);
 	
@@ -468,7 +450,7 @@ int link_cell_update(t_moldyn *moldyn) {
 	for(i=0;i<lc->cells;i++)
 		list_destroy(&(moldyn->lc.subcell[i]));
 	
-	for(count=0;count<moedyn->count;count++) {
+	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;
@@ -487,7 +469,7 @@ int link_cell_neighbour_index(t_moldyn *moldyn,int i,int j,int k,t_list *cell) {
 	int ci,cj,ck;
 	int nx,ny,nz;
 	int x,y,z;
-	unsigned char bx,by,bz;
+	u8 bx,by,bz;
 
 	lc=&(moldyn->lc);
 	nx=lc->nx;
@@ -547,8 +529,42 @@ int link_cell_shutdown(t_moldyn *moldyn) {
 	for(i=0;i<lc->nx*lc->ny*lc->nz;i++)
 		list_shutdown(&(moldyn->lc.subcell[i]));
 
-	if(lc->listfd) close(lc->listfd);
+	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;
 }
 
@@ -562,13 +578,16 @@ int link_cell_shutdown(t_moldyn *moldyn) {
 
 int moldyn_integrate(t_moldyn *moldyn) {
 
-	int i;
-	unsigned int e,m,s,d,v;
+	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);
 
@@ -576,38 +595,49 @@ int moldyn_integrate(t_moldyn *moldyn) {
 	e=moldyn->ewrite;
 	m=moldyn->mwrite;
 	s=moldyn->swrite;
-	d=moldyn->dwrite;
 	v=moldyn->vwrite;
 
-	if(!(moldyn->lvstat&MOLDYN_LVSTAT_INITIALIZED)) {
-		printf("[moldyn] warning, lv system not initialized\n");
-		return -1;
-	}
-
 	/* sqaure of some variables */
 	moldyn->tau_square=moldyn->tau*moldyn->tau;
 	moldyn->cutoff_square=moldyn->cutoff*moldyn->cutoff;
 
 	/* calculate initial forces */
-	moldyn->potential_force_function(moldyn);
+	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\n",i*moldyn->tau,
+				        "%.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->atom,moldyn->count);
+				p=get_total_p(moldyn);
 				dprintf(moldyn->mfd,
-				        "%.15f %.45f\n",i*moldyn->tau,
+				        "%.15f %.45f\n",moldyn->time,
 				        v3_norm(&p));
 			}
 		}
@@ -627,12 +657,19 @@ int moldyn_integrate(t_moldyn *moldyn) {
 		}
 		if(v) {
 			if(!(i%v)) {
-				visual_atoms(moldyn->visual,i*moldyn->tau,
+				visual_atoms(&(moldyn->vis),moldyn->time,
 				             moldyn->atom,moldyn->count);
-				printf("\rsteps: %d",i);
+				printf("\rsched: %d, steps: %d",sched,i);
 				fflush(stdout);
 			}
 		}
+
+	}
+
+		/* check for hooks */
+		if(schedule->hook)
+			schedule->hook(moldyn,schedule->hook_params);
+
 	}
 
 	return 0;
@@ -666,15 +703,11 @@ int velocity_verlet(t_moldyn *moldyn) {
 	}
 
 	/* neighbour list update */
-printf("list update ...\n");
 	link_cell_update(moldyn);
-printf("done\n");
 
 	/* forces depending on chosen potential */
-printf("calc potential/force ...\n");
 	potential_force_calc(moldyn);
 	//moldyn->potential_force_function(moldyn);
-printf("done\n");
 
 	for(i=0;i<count;i++) {
 		/* again velocities */
@@ -694,29 +727,22 @@ printf("done\n");
 
 /* generic potential and force calculation */
 
-#define		CREATE_CELL_LIST(nb_list) \
-	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,\
-	                          nb_list);
-
-
 int potential_force_calc(t_moldyn *moldyn) {
 
-	int i,count;
-	t_atom *atom;
+	int i,j,k,count;
+	t_atom *atom,*btom,*ktom;
 	t_linkcell *lc;
 	t_list neighbour[27];
-	t_list *this;
-	double u;
+	t_list *this,*thisk,*neighbourk;
+	u8 bc,bck;
+	int countn,dnlc;
 
 	count=moldyn->count;
 	atom=moldyn->atom;
 	lc=&(moldyn->lc);
 
 	/* reset energy */
-	u=0.0;
+	moldyn->energy=0.0;
 
 	for(i=0;i<count;i++) {
 	
@@ -724,667 +750,489 @@ int potential_force_calc(t_moldyn *moldyn) {
 		v3_zero(&(atom[i].f));
 
 		/* single particle potential/force */
-		if(moldyn->status&MOLDYN_STAT_1BP)
-			moldyn->pf_func1b(moldyn,&(atom[i]));
+		if(atom[i].attr&ATOM_ATTR_1BP)
+			moldyn->func1b(moldyn,&(atom[i]));
 
 		/* 2 body pair potential/force */
-		if(moldyn->status&MOLDYN_STAT_2BP) {
+		if(atom[i].attr&(ATOM_ATTR_2BP|ATOM_ATTR_3BP)) {
 		
-			CREATE_CELL_LIST(neighbour);
-
-			/*
-			 * processing cell of atom i
-			 * => no need to check for empty list
-			 *    (1 element at minimum)
-			 */
-
-			this=&(neighbour[0]);
-			list_reset(this);
-			do {
-				btom=this->current->data;
-				if(btom!=&(atom[i]))
-					moldyn->pf_func2b(moldyn,
-					                  &(atom[i]),btom);
-			} while(list_next(this)!=L_NO_NEXT_ELEMENT);
-
-			/*
-			 * direct neighbour cells
-			 * => no boundary condition check necessary
-			 */
-			for(j=0;j<lc->dnlc;j++) {
-				this=&(neighbour[j]);
-				list_reset(this);
-				if(this->start!=NULL) {
-					do {
-						btom=this->current->data;
-						moldyn->pf_func2b(moldyn,
-						                  &(atom[i]),
-						                  btom);
-					} while(list_next(this)!=\
-					        L_NO_NEXT_ELEMENT);
-			}
+			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);
 
-			/*
-			 * neighbour cells due to periodic bc
-			 * => check boundary conditions
-			 */
-			for(j=lc->dnlc;j<lc->countn;j++) {
-				this=&(neighbour[j]);
-				list_reset(this);
-				if(this->start!=NULL) {
-					do {
-						btom=this->current->data;
-						moldyn->pf_func2b(moldyn,
-						                  &(atom[i]),
-						                  btom);
+			countn=lc->countn;
+			dnlc=lc->dnlc;
 
-			}
+			for(j=0;j<countn;j++) {
 
-		}
-
-	return 0;
-}
-
-
-/* harmonic oscillator potential and force */
-
-int harmonic_oscillator(t_moldyn *moldyn) {
+				this=&(neighbour[j]);
+				list_reset(this);
 
-	t_ho_params *params;
-	t_atom *atom,*btom;
-	t_linkcell *lc;
-	t_list *this,neighbour[27];
-	int i,j,c;
-	int count;
-	t_3dvec force,distance;
-	double d,u;
-	double sc,equi_dist;
-	int ni,nj,nk;
+				if(this->start==NULL)
+					continue;
 
-	params=moldyn->pot_params;
-	atom=moldyn->atom;
-	lc=&(moldyn->lc);
-	sc=params->spring_constant;
-	equi_dist=params->equilibrium_distance;
-	count=moldyn->count;
+				bc=(j<dnlc)?0:1;
 
-	/* reset energy counter */
-	u=0.0;
+				do {
+					btom=this->current->data;
 
-	for(i=0;i<count;i++) {
-		/* reset force */
-		v3_zero(&(atom[i].f));
+					if(btom==&(atom[i]))
+						continue;
 
-		/* determine cell + neighbours */
-		ni=(atom[i].r.x+(moldyn->dim.x/2))/lc->x;
-		nj=(atom[i].r.y+(moldyn->dim.y/2))/lc->y;
-		nk=(atom[i].r.z+(moldyn->dim.z/2))/lc->z;
-		c=link_cell_neighbour_index(moldyn,ni,nj,nk,neighbour);
-
-		/*
-		 * processing cell of atom i
-		 * => no need to check for empty list (1 element at minimum)
-		 */
-		this=&(neighbour[0]);
-		list_reset(this);
-		do {
-			btom=this->current->data;
-			if(btom==&(atom[i]))
-				continue;
-			v3_sub(&distance,&(atom[i].r),&(btom->r));
-			d=v3_norm(&distance);
-			if(d<=moldyn->cutoff) {
-				u+=(0.5*sc*(d-equi_dist)*(d-equi_dist));
-				v3_scale(&force,&distance,
-				         -sc*(1.0-(equi_dist/d)));
-				v3_add(&(atom[i].f),&(atom[i].f),&force);
-			}
-		} while(list_next(this)!=L_NO_NEXT_ELEMENT);
-
-		/*
-		 * direct neighbour cells
-		 * => no boundary condition check necessary
-		 */
-		for(j=1;j<c;j++) {
-			this=&(neighbour[j]);
-			list_reset(this); /* there might not be a single atom */
-			if(this->start!=NULL) {
-
-			do {
-				btom=this->current->data;
-				v3_sub(&distance,&(atom[i].r),&(btom->r));
-				d=v3_norm(&distance);
-				if(d<=moldyn->cutoff) {
-					u+=(0.5*sc*(d-equi_dist)*(d-equi_dist));
-					v3_scale(&force,&distance,
-					         -sc*(1.0-(equi_dist/d)));
-					v3_add(&(atom[i].f),&(atom[i].f),
-					       &force);
-				}
-			} while(list_next(this)!=L_NO_NEXT_ELEMENT);
+					if((btom->attr&ATOM_ATTR_2BP)&
+					   (atom[i].attr&ATOM_ATTR_2BP))
+						moldyn->func2b(moldyn,
+						               &(atom[i]),
+						               btom,
+						               bc);
 
-			}
-		}
+					/* 3 body potential/force */
 
-		/*
-		 * indirect neighbour cells
-		 * => check boundary conditions
-		 */
-		for(j=c;j<27;j++) {
-			this=&(neighbour[j]);
-			list_reset(this); /* check boundary conditions */
-			if(this->start!=NULL) {
-
-			do {
-				btom=this->current->data;
-				v3_sub(&distance,&(atom[i].r),&(btom->r));
-				v3_per_bound(&distance,&(moldyn->dim));
-				d=v3_norm(&distance);
-				if(d<=moldyn->cutoff) {
-					u+=(0.5*sc*(d-equi_dist)*(d-equi_dist));
-					v3_scale(&force,&distance,
-					         -sc*(1.0-(equi_dist/d)));
-					v3_add(&(atom[i].f),&(atom[i].f),
-					       &force);
-				}
-			} while(list_next(this)!=L_NO_NEXT_ELEMENT);
+					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);
 
-	moldyn->energy=0.5*u;
+					for(k=0;k<lc->countn;k++) {
 
-	return 0;
-}
+						thisk=&(neighbourk[k]);
+						list_reset(thisk);
+					
+						if(thisk->start==NULL)
+							continue;
 
-/* lennard jones potential & force for one sort of atoms */
- 
-int lennard_jones(t_moldyn *moldyn) {
+						bck=(k<lc->dnlc)?0:1;
 
-	t_lj_params *params;
-	t_atom *atom,*btom;
-	t_linkcell *lc;
-	t_list *this,neighbour[27];
-	int i,j,c;
-	int count;
-	t_3dvec force,distance;
-	double d,h1,h2,u;
-	double eps,sig6,sig12;
-	int ni,nj,nk;
+						do {
 
-	params=moldyn->pot_params;
-	atom=moldyn->atom;
-	lc=&(moldyn->lc);
-	count=moldyn->count;
-	eps=params->epsilon4;
-	sig6=params->sigma6;
-	sig12=params->sigma12;
+			ktom=thisk->current->data;
 
-	/* reset energy counter */
-	u=0.0;
+			if(!(ktom->attr&ATOM_ATTR_3BP))
+				continue;
 
-	for(i=0;i<count;i++) {
-		/* reset force */
-		v3_zero(&(atom[i].f));
+			if(ktom==btom)
+				continue;
 
-		/* determine cell + neighbours */
-		ni=(atom[i].r.x+(moldyn->dim.x/2))/lc->x;
-		nj=(atom[i].r.y+(moldyn->dim.y/2))/lc->y;
-		nk=(atom[i].r.z+(moldyn->dim.z/2))/lc->z;
-		c=link_cell_neighbour_index(moldyn,ni,nj,nk,neighbour);
-
-		/* processing cell of atom i */
-		this=&(neighbour[0]);
-		list_reset(this); /* list has 1 element at minimum */
-		do {
-			btom=this->current->data;
-			if(btom==&(atom[i]))
+			if(ktom==&(atom[i]))
 				continue;
-			v3_sub(&distance,&(atom[i].r),&(btom->r));
-			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 */
-				u+=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(&(atom[i].f),&(atom[i].f),&force);
-			}
-		} while(list_next(this)!=L_NO_NEXT_ELEMENT);
-
-		/* neighbours not doing boundary condition overflow */
-		for(j=1;j<c;j++) {
-			this=&(neighbour[j]);
-			list_reset(this); /* there might not be a single atom */
-			if(this->start!=NULL) {
-
-			do {
-				btom=this->current->data;
-				v3_sub(&distance,&(atom[i].r),&(btom->r));
-				d=v3_absolute_square(&distance); /* 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 */
-					u+=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(&(atom[i].f),&(atom[i].f),
-					       &force);
-				}
-			} while(list_next(this)!=L_NO_NEXT_ELEMENT);
-				
-			}
-		}
 
-		/* neighbours due to boundary conditions */
-		for(j=c;j<27;j++) {
-			this=&(neighbour[j]);
-			list_reset(this); /* check boundary conditions */
-			if(this->start!=NULL) {
-
-			do {
-				btom=this->current->data;
-				v3_sub(&distance,&(atom[i].r),&(btom->r));
-				v3_per_bound(&distance,&(moldyn->dim));
-				d=v3_absolute_square(&distance); /* 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 */
-					u+=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(&(atom[i].f),&(atom[i].f),
-					       &force);
-				}
-			} while(list_next(this)!=L_NO_NEXT_ELEMENT);
+			moldyn->func3b(moldyn,&(atom[i]),btom,ktom,bck);
 
+						} while(list_next(thisk)!=\
+						        L_NO_NEXT_ELEMENT);
+
+					}
+					
+				} while(list_next(this)!=L_NO_NEXT_ELEMENT);
 			}
 		}
 	}
 
-	moldyn->energy=0.5*u;
-	
 	return 0;
 }
 
-/* tersoff potential & force for 2 sorts of atoms */
-
-int tersoff(t_moldyn *moldyn) {
-
-	t_tersoff_params *params;
-	t_atom *atom,*btom,*ktom;
-	t_linkcell *lc;
-	t_list *this,*thisk,neighbour[27],neighbourk[27];
-	int i,j,k,c,ck;
-	int count;
-	double u;
-	int ni,nj,nk;
-	int ki,kj,kk;
-	
+/*
+ * periodic boundayr checking
+ */
 
-	params=moldyn->pot_params;
-	atom=moldyn->atom;
-	lc=&(moldyn->lc);
-	count=moldyn->count;
+int check_per_bound(t_moldyn *moldyn,t_3dvec *a) {
 	
-	/* reset energy counter */
-	u=0.0;
+	double x,y,z;
+	t_3dvec *dim;
 
-	for(i=0;i<count;i++) {
-		/* reset force */
-		v3_zero(&(atom[i].f));
+	dim=&(moldyn->dim);
 
-		/* determin cell neighbours */
-		ni=(atom[i].r.x+(moldyn->dim.x/2))/lc->x;
-		nj=(atom[i].r.y+(moldyn->dim.y/2))/lc->y;
-		nk=(atom[i].r.z+(moldyn->dim.z/2))/lc->z;
-		c=link_cell_neighbour_index(moldyn,ni,nj,nk,neighbour);
-
-		/*
-		 * processing cell of atom i
-		 * => no need to check for empty list (1 element at minimum)
-		 */
-		this=&(neighbour[0]);
-		list_reset(this);
-		do {
-			btom=this->current->data;
-			if(btom==&(atom[i]))
-				continue;
+	x=0.5*dim->x;
+	y=0.5*dim->y;
+	z=0.5*dim->z;
 
-			/* 2 body stuff */
-
-			/* we need: f_c, df_c, f_r, df_r */
-
-			v3_sub(&dist_ij,btom,&(atom[i]));
-			d_ij=v3_norm(&dist_ij);
-			if(d_ij<=S) {
-
-				/* determine the tersoff parameters */
-				if(atom[i].element!=btom->element) {
-				S=sqrt(TERSOFF_S[e1]*TERSOFF_S[e2]);
-				R=R_m;
-				A=;
-				lambda=;
-				B=;
-				mu=;
-				chi=;
-				beta=;
-				betaN=;
-
-				if(d_ij<=R) {
-					df_r=-lambda*A*exp(-lambda*d_ij)/d_ij;
-					v3_scale(&force,&dist_ij,df_r);
-					v3_add(&(atom[i].f),&(atom[i].f),
-						&force);
-				}
-				else {
-					s_r=S-R;
-					arg1=PI*(d_ij-R)/s_r;
-					f_c=0.5+0.5*cos(arg1);
-					df_c=-0.5*sin(arg1)*(PI/(s_r*d_ij));
-					f_r=A*exp(-lambda*d_ij);
-					df_r=-lambda*f_r/d_ij;
-					scale=df_c*f_r+df_r*f_c;
-					v3_scale(&force,&dist_ij,scale);
-					v3_add(&(atom[i].f),&(atom[i].f),
-					       &force);
-				}
-			}
-			else 
-				continue;		
-
-			
-			/* end 2 body stuff */ 
-
-			/* determine cell neighbours of btom */
-			ki=(btom->r.x+(moldyn->dim.x/2))/lc->x;
-			kj=(btom->r.y+(moldyn->dim.y/2))/lc->y;
-			kk=(btom->r.z+(moldyn->dim.z/2))/lc->z;
-			ck=link_cell_neighbour_index(moldyn,ki,kj,kk,
-			                             neighbourk);
-
-			/* go for zeta - 3 body stuff! */
-			zeta=0.0;
-			d_ij2=d_ij*d_ij;
-
-			/* cell of btom */
-			thisk=&(neighbourk[0]);
-			list_reset(thisk);
-			do {
-				ktom=thisk->current->data;
-				if(ktom==btom)
-					continue;
-				if(ktom==&(atom[i]))
-					continue;
-				
-				/* 3 body stuff (1) */
-				
-				v3_sub(&dist_ik,ktom,&(atom[i]));
-				d_ik=v3_norm(&dist_ik);
-				if(d_ik<=Sik) {
-
-				Rik=;
-				Sik=;
-				Aik=;
-				lambda_ik=;
-				Bik=;
-				mu_ik=;
-				omega_ik=;
-				c_i=;
-				d_i=;
-				h_i=;
-			
-
-					if(d_ik<=Rik) {
-						f_cik=1.0;
-						df_cik=0.0;
-					}
-					else {
-						sik_rik=Sik-Rik;
-						arg1ik=PI*(d_ik-Rik)/sik_rik;
-						f_cik=0.5+0.5*cos(arg1ik);
-						df_cik=-0.5*sin(arg1ik)* \
-						       (PI/(sik_rik*d_ik));
-						f_rik=Aik*exp(-lambda_ik*d_ik);
-						f_aik=-Bik*exp(-mu_ik*d_ik);
-					}
-			
-					v3_sub(&distance_jk,ktom,btom);
-					cos_theta=(d_ij2+d_ik*d_ik-d_jk*d_jk)/\
-					          (2*d_ij*d_ik);
-					sin_theta=sqrt(1.0/\
-					          (cos_theta*cos_theta));
-					theta=arccos(cos_theta);
-
-					
-				}
-				else
-					continue;
-
-				/* end 3 body stuff (1) */
-
-
-			} while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
-
-			/* direct neighbours of btom cell */
-			for(k=1;k<ck;k++) {
-				thisk=&(neighbourk[k]);
-				list_reset(thisk);
-				if(thisk->start!=NULL) {
-
-				do {
-					ktom=thisk->current->data;
-					if(ktom==&(atom[i]))
-						continue;
-
-				/* 3 body stuff (2) */
-
-				} while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
-
-				}
-			}
-
-			/* indirect neighbours of btom cell */
-			for(k=ck;k<27;k++) {
-				thisk=&(neighbourk[k]);
-				list_reset(thisk);
-				if(thisk->start!=NULL) {
-
-				do {
-					ktom=thisk->current->data;
-					if(ktom==&(atom[i]))
-						continue;
+	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;
+	}
 
-				/* 3 body stuff */
+	return 0;
+}
+        
 
-				} while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+/*
+ * example potentials
+ */
 
-				}
-			}
+/* harmonic oscillator potential and force */
 
+int harmonic_oscillator(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 
-		} while(list_next(this)!=L_NO_NEXT_ELEMENT);
+	t_ho_params *params;
+	t_3dvec force,distance;
+	double d;
+	double sc,equi_dist;
 
-		/*
-		 * direct neighbour cells of atom i
-		 */
-		for(j=1;j<c;j++) {
-			this=&(neighbour[j]);
-			list_reset(this);
-			if(this->start!=NULL) {
+	params=moldyn->pot2b_params;
+	sc=params->spring_constant;
+	equi_dist=params->equilibrium_distance;
 
-			do {
-				btom=this->current->data;
+	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);
+	}
 
-				/* 2 body stuff */
+	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) {
 
-			/* determine cell neighbours of btom */
-			ki=(btom->r.x+(moldyn->dim.x/2))/lc->x;
-			kj=(btom->r.y+(moldyn->dim.y/2))/lc->y;
-			kk=(btom->r.z+(moldyn->dim.z/2))/lc->z;
-			ck=link_cell_neighbour_index(moldyn,ki,kj,kk,
-			                             neighbourk);
+	t_lj_params *params;
+	t_3dvec force,distance;
+	double d,h1,h2;
+	double eps,sig6,sig12;
 
-			/* cell of btom */
-			thisk=&(neighbourk[0]);
-			list_reset(thisk);
-			do {
-				ktom=thisk->current->data;
-				if(ktom==btom)
-					continue;
-				if(ktom==&(atom[i]))
-					continue;
-				
-				/* 3 body stuff (1) */
+	params=moldyn->pot2b_params;
+	eps=params->epsilon4;
+	sig6=params->sigma6;
+	sig12=params->sigma12;
 
-			} while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+	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);
+	}
 
-			/* direct neighbours of btom cell */
-			for(k=1;k<ck;k++) {
-				thisk=&(neighbourk[k]);
-				list_reset(thisk);
-				if(thisk->start!=NULL) {
+	return 0;
+}
 
-				do {
-					ktom=thisk->current->data;
-					if(ktom==&(atom[i]))
-						continue;
+/*
+ * tersoff potential & force for 2 sorts of atoms
+ */
 
-				/* 3 body stuff (2) */
+/* tersoff 1 body part */
+int tersoff_mult_1bp(t_moldyn *moldyn,t_atom *ai) {
 
-				} while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+	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
+	 */
 
-			/* indirect neighbours of btom cell */
-			for(k=ck;k<27;k++) {
-				thisk=&(neighbourk[k]);
-				list_reset(thisk);
-				if(thisk->start!=NULL) {
+	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]);
 
-				do {
-					ktom=thisk->current->data;
-					if(ktom==&(atom[i]))
-						continue;
+	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;
 
-				/* 3 body stuff (3) */
+	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
+	 */
 
-				} while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+	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;
 
-			} while(list_next(this)!=L_NO_NEXT_ELEMENT);
+	/* 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);
 
-		/*
-		 * indirect neighbour cells of atom i
-		 */
-		for(j=c;j<27;j++) {
-			this=&(neighbour[j]);
-			list_reset(this);
-			if(this->start!=NULL) {
-
-			do {
-				btom=this->current->data;
-
-				/* 2 body stuff */
-
-
-			/* determine cell neighbours of btom */
-			ki=(btom->r.x+(moldyn->dim.x/2))/lc->x;
-			kj=(btom->r.y+(moldyn->dim.y/2))/lc->y;
-			kk=(btom->r.z+(moldyn->dim.z/2))/lc->z;
-			ck=link_cell_neighbour_index(moldyn,ki,kj,kk,
-			                             neighbourk);
-
-			/* cell of btom */
-			thisk=&(neighbourk[0]);
-			list_reset(thisk);
-			do {
-				ktom=thisk->current->data;
-				if(ktom==btom)
-					continue;
-				if(ktom==&(atom[i]))
-					continue;
-				
-				/* 3 body stuff (1) */
+	/* save for use in 3bp */
+	exchange->d_ij=d_ij;
 
-			} while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+	if(d_ij>S)
+		return 0;
 
-			/* direct neighbours of btom cell */
-			for(k=1;k<ck;k++) {
-				thisk=&(neighbourk[k]);
-				list_reset(thisk);
-				if(thisk->start!=NULL) {
+	f_r=A*exp(-lambda*d_ij);
+	df_r=-lambda*f_r/d_ij;
 
-				do {
-					ktom=thisk->current->data;
-					if(ktom==&(atom[i]))
-						continue;
+	/* 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;
 
-				/* 3 body stuff (2) */
+	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);
+	}
 
-				} while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+	/* 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;
 
-			/* indirect neighbours of btom cell */
-			for(k=ck;k<27;k++) {
-				thisk=&(neighbourk[k]);
-				list_reset(thisk);
-				if(thisk->start!=NULL) {
+	/* enable the run of 3bp function */
+	exchange->run3bp=1;
 
-				do {
-					ktom=thisk->current->data;
-					if(ktom==&(atom[i]))
-						continue;
+	return 0;
+}
 
-				/* 3 body stuff (3) */
+/* 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;
 
-				} while(list_next(thisk)!=L_NO_NEXT_ELEMENT);
+	/*
+	 * 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! */
 
-			} while(list_next(this)!=L_NO_NEXT_ELEMENT);
+	/*
+	 * 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;
 	}
 
-	moldyn->energy=0.5*u;
+	/* 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);
+
+	/* 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;
 }