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lammps/src/KSPACE/pppm_tip4p.cpp
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pppm_tip4p.cpp
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/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
http://lammps.sandia.gov, Sandia National Laboratories
Steve Plimpton, sjplimp@sandia.gov
Copyright (2003) Sandia Corporation. Under the terms of Contract
DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
certain rights in this software. This software is distributed under
the GNU General Public License.
See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */
/* ----------------------------------------------------------------------
Contributing authors: Amalie Frischknecht and Ahmed Ismail (SNL)
------------------------------------------------------------------------- */
#include "math.h"
#include "pppm_tip4p.h"
#include "atom.h"
#include "domain.h"
#include "force.h"
#include "memory.h"
#include "error.h"
using namespace LAMMPS_NS;
#define OFFSET 16384
#ifdef FFT_SINGLE
#define ZEROF 0.0f
#define ONEF 1.0f
#else
#define ZEROF 0.0
#define ONEF 1.0
#endif
/* ---------------------------------------------------------------------- */
PPPMTIP4P::PPPMTIP4P(LAMMPS *lmp, int narg, char **arg) :
PPPM(lmp, narg, arg) {}
/* ---------------------------------------------------------------------- */
void PPPMTIP4P::init()
{
// TIP4P PPPM requires newton on, b/c it computes forces on ghost atoms
if (force->newton == 0)
error->all(FLERR,"Kspace style pppm/tip4p requires newton on");
PPPM::init();
}
/* ----------------------------------------------------------------------
find center grid pt for each of my particles
check that full stencil for the particle will fit in my 3d brick
store central grid pt indices in part2grid array
------------------------------------------------------------------------- */
void PPPMTIP4P::particle_map()
{
int nx,ny,nz,iH1,iH2;
double *xi,xM[3];
int *type = atom->type;
double **x = atom->x;
int nlocal = atom->nlocal;
int flag = 0;
for (int i = 0; i < nlocal; i++) {
if (type[i] == typeO) {
find_M(i,iH1,iH2,xM);
xi = xM;
} else xi = x[i];
// (nx,ny,nz) = global coords of grid pt to "lower left" of charge
// current particle coord can be outside global and local box
// add/subtract OFFSET to avoid int(-0.75) = 0 when want it to be -1
nx = static_cast<int> ((xi[0]-boxlo[0])*delxinv+shift) - OFFSET;
ny = static_cast<int> ((xi[1]-boxlo[1])*delyinv+shift) - OFFSET;
nz = static_cast<int> ((xi[2]-boxlo[2])*delzinv+shift) - OFFSET;
part2grid[i][0] = nx;
part2grid[i][1] = ny;
part2grid[i][2] = nz;
// check that entire stencil around nx,ny,nz will fit in my 3d brick
if (nx+nlower < nxlo_out || nx+nupper > nxhi_out ||
ny+nlower < nylo_out || ny+nupper > nyhi_out ||
nz+nlower < nzlo_out || nz+nupper > nzhi_out) flag++;
}
int flag_all;
MPI_Allreduce(&flag,&flag_all,1,MPI_INT,MPI_SUM,world);
if (flag_all) error->all(FLERR,"Out of range atoms - cannot compute PPPM");
}
/* ----------------------------------------------------------------------
create discretized "density" on section of global grid due to my particles
density(x,y,z) = charge "density" at grid points of my 3d brick
(nxlo:nxhi,nylo:nyhi,nzlo:nzhi) is extent of my brick (including ghosts)
in global grid
------------------------------------------------------------------------- */
void PPPMTIP4P::make_rho()
{
int i,l,m,n,nx,ny,nz,mx,my,mz,iH1,iH2;
FFT_SCALAR dx,dy,dz,x0,y0,z0;
double *xi,xM[3];
// clear 3d density array
FFT_SCALAR *vec = &density_brick[nzlo_out][nylo_out][nxlo_out];
for (i = 0; i < ngrid; i++) vec[i] = ZEROF;
// loop over my charges, add their contribution to nearby grid points
// (nx,ny,nz) = global coords of grid pt to "lower left" of charge
// (dx,dy,dz) = distance to "lower left" grid pt
// (mx,my,mz) = global coords of moving stencil pt
int *type = atom->type;
double *q = atom->q;
double **x = atom->x;
int nlocal = atom->nlocal;
for (int i = 0; i < nlocal; i++) {
if (type[i] == typeO) {
find_M(i,iH1,iH2,xM);
xi = xM;
} else xi = x[i];
nx = part2grid[i][0];
ny = part2grid[i][1];
nz = part2grid[i][2];
dx = nx+shiftone - (xi[0]-boxlo[0])*delxinv;
dy = ny+shiftone - (xi[1]-boxlo[1])*delyinv;
dz = nz+shiftone - (xi[2]-boxlo[2])*delzinv;
compute_rho1d(dx,dy,dz);
z0 = delvolinv * q[i];
for (n = nlower; n <= nupper; n++) {
mz = n+nz;
y0 = z0*rho1d[2][n];
for (m = nlower; m <= nupper; m++) {
my = m+ny;
x0 = y0*rho1d[1][m];
for (l = nlower; l <= nupper; l++) {
mx = l+nx;
density_brick[mz][my][mx] += x0*rho1d[0][l];
}
}
}
}
}
/* ----------------------------------------------------------------------
interpolate from grid to get electric field & force on my particles
------------------------------------------------------------------------- */
void PPPMTIP4P::fieldforce()
{
int i,l,m,n,nx,ny,nz,mx,my,mz;
FFT_SCALAR dx,dy,dz,x0,y0,z0;
FFT_SCALAR ekx,eky,ekz;
double *xi;
int iH1,iH2;
double xM[3];
double fx,fy,fz;
double ddotf, rOMx, rOMy, rOMz, f1x, f1y, f1z;
// loop over my charges, interpolate electric field from nearby grid points
// (nx,ny,nz) = global coords of grid pt to "lower left" of charge
// (dx,dy,dz) = distance to "lower left" grid pt
// (mx,my,mz) = global coords of moving stencil pt
// ek = 3 components of E-field on particle
double *q = atom->q;
double **x = atom->x;
double **f = atom->f;
int *type = atom->type;
int nlocal = atom->nlocal;
for (i = 0; i < nlocal; i++) {
if (type[i] == typeO) {
find_M(i,iH1,iH2,xM);
xi = xM;
} else xi = x[i];
nx = part2grid[i][0];
ny = part2grid[i][1];
nz = part2grid[i][2];
dx = nx+shiftone - (xi[0]-boxlo[0])*delxinv;
dy = ny+shiftone - (xi[1]-boxlo[1])*delyinv;
dz = nz+shiftone - (xi[2]-boxlo[2])*delzinv;
compute_rho1d(dx,dy,dz);
ekx = eky = ekz = ZEROF;
for (n = nlower; n <= nupper; n++) {
mz = n+nz;
z0 = rho1d[2][n];
for (m = nlower; m <= nupper; m++) {
my = m+ny;
y0 = z0*rho1d[1][m];
for (l = nlower; l <= nupper; l++) {
mx = l+nx;
x0 = y0*rho1d[0][l];
ekx -= x0*vdx_brick[mz][my][mx];
eky -= x0*vdy_brick[mz][my][mx];
ekz -= x0*vdz_brick[mz][my][mx];
}
}
}
// convert E-field to force
const double qfactor = force->qqrd2e * scale * q[i];
if (type[i] != typeO) {
f[i][0] += qfactor*ekx;
f[i][1] += qfactor*eky;
f[i][2] += qfactor*ekz;
} else {
fx = qfactor * ekx;
fy = qfactor * eky;
fz = qfactor * ekz;
find_M(i,iH1,iH2,xM);
rOMx = xM[0] - x[i][0];
rOMy = xM[1] - x[i][1];
rOMz = xM[2] - x[i][2];
ddotf = (rOMx * fx + rOMy * fy + rOMz * fz) / (qdist * qdist);
f1x = ddotf * rOMx;
f1y = ddotf * rOMy;
f1z = ddotf * rOMz;
f[i][0] += fx - alpha * (fx - f1x);
f[i][1] += fy - alpha * (fy - f1y);
f[i][2] += fz - alpha * (fz - f1z);
f[iH1][0] += 0.5*alpha*(fx - f1x);
f[iH1][1] += 0.5*alpha*(fy - f1y);
f[iH1][2] += 0.5*alpha*(fz - f1z);
f[iH2][0] += 0.5*alpha*(fx - f1x);
f[iH2][1] += 0.5*alpha*(fy - f1y);
f[iH2][2] += 0.5*alpha*(fz - f1z);
}
}
}
/* ----------------------------------------------------------------------
find 2 H atoms bonded to O atom i
compute position xM of fictitious charge site for O atom
also return local indices iH1,iH2 of H atoms
------------------------------------------------------------------------- */
void PPPMTIP4P::find_M(int i, int &iH1, int &iH2, double *xM)
{
iH1 = atom->map(atom->tag[i] + 1);
iH2 = atom->map(atom->tag[i] + 2);
if (iH1 == -1 || iH2 == -1) error->one(FLERR,"TIP4P hydrogen is missing");
if (atom->type[iH1] != typeH || atom->type[iH2] != typeH)
error->one(FLERR,"TIP4P hydrogen has incorrect atom type");
double **x = atom->x;
double delx1 = x[iH1][0] - x[i][0];
double dely1 = x[iH1][1] - x[i][1];
double delz1 = x[iH1][2] - x[i][2];
domain->minimum_image(delx1,dely1,delz1);
double delx2 = x[iH2][0] - x[i][0];
double dely2 = x[iH2][1] - x[i][1];
double delz2 = x[iH2][2] - x[i][2];
domain->minimum_image(delx2,dely2,delz2);
xM[0] = x[i][0] + alpha * 0.5 * (delx1 + delx2);
xM[1] = x[i][1] + alpha * 0.5 * (dely1 + dely2);
xM[2] = x[i][2] + alpha * 0.5 * (delz1 + delz2);
}
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