implement fix wall/morse based on fix wall/region and fix wall/harmonic

2019-08-20 13:29:09 -04:00
parent 82b3fad152
commit 6a584672e8
5 changed files with 172 additions and 6 deletions
--- a/src/fix_wall_morse.cpp
+++ b/src/fix_wall_morse.cpp
@ -0,0 +1,87 @@
+/* ----------------------------------------------------------------------
+   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.
+------------------------------------------------------------------------- */
+
+#include "fix_wall_morse.h"
+#include <cmath>
+#include "atom.h"
+#include "error.h"
+
+using namespace LAMMPS_NS;
+using namespace FixConst;
+
+/* ---------------------------------------------------------------------- */
+
+FixWallMorse::FixWallMorse(LAMMPS *lmp, int narg, char **arg) :
+  FixWall(lmp, narg, arg)
+{
+  dynamic_group_allow = 1;
+}
+
+/* ---------------------------------------------------------------------- */
+
+void FixWallMorse::precompute(int m)
+{
+  coeff1[m] = 2.0 * epsilon[m] * alpha[m];
+  const double alpha_dr = -alpha[m] * (cutoff[m] - sigma[m]);
+  offset[m] = epsilon[m] * (exp(2.0*alpha_dr) - 2.0*exp(alpha_dr));
+}
+
+/* ----------------------------------------------------------------------
+   interaction of all particles in group with a wall
+   m = index of wall coeffs
+   which = xlo,xhi,ylo,yhi,zlo,zhi
+   error if any particle is on or behind wall
+------------------------------------------------------------------------- */
+
+void FixWallMorse::wall_particle(int m, int which, double coord)
+{
+  double delta,fwall;
+  double vn;
+
+  double **x = atom->x;
+  double **f = atom->f;
+  int *mask = atom->mask;
+  int nlocal = atom->nlocal;
+
+  int dim = which / 2;
+  int side = which % 2;
+  if (side == 0) side = -1;
+
+  int onflag = 0;
+
+  for (int i = 0; i < nlocal; i++) {
+    if (mask[i] & groupbit) {
+      if (side < 0) delta = x[i][dim] - coord;
+      else delta = coord - x[i][dim];
+      if (delta >= cutoff[m]) continue;
+      if (delta <= 0.0) {
+        onflag = 1;
+        continue;
+      }
+      double dr = delta - sigma[m];
+      double dexp = exp(-alpha[m] * dr);
+      fwall = side * coeff1[m] * (dexp*dexp - dexp) / delta;
+      ewall[0] += epsilon[m] * (dexp*dexp - 2.0*dexp) - offset[m];
+      f[i][dim] -= fwall;
+      ewall[m+1] += fwall;
+
+      if (evflag) {
+        if (side < 0) vn = -fwall*delta;
+        else vn = fwall*delta;
+        v_tally(dim, i, vn);
+      }
+    }
+  }
+
+  if (onflag) error->one(FLERR,"Particle on or inside fix wall surface");
+}