+ 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;
+
+printf("DEBUG: count = %d\n",count);
+ 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)) {
+
+printf("DEBUG: processing atom %d\n",i);
+ 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;
+
+printf("DEBUG: countn = %d - dnslc = %d\n",countn,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))
+printf("DEBUG: calling func2b\n");
+ 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);