/* ----------------------------------------------------------------------
   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
   https://www.lammps.org/, Sandia National Laboratories
   LAMMPS development team: developers@lammps.org

   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 author: Jonathan Lee (Sandia)
------------------------------------------------------------------------- */

#include "fix_wall_lj1043.h"

#include "atom.h"
#include "math_const.h"
#include "math_special.h"

#include <cmath>

using namespace LAMMPS_NS;
using MathConst::MY_2PI;
using MathSpecial::powint;

/* ---------------------------------------------------------------------- */

FixWallLJ1043::FixWallLJ1043(LAMMPS *lmp, int narg, char **arg) : FixWall(lmp, narg, arg)
{
  dynamic_group_allow = 1;
}

/* ---------------------------------------------------------------------- */

void FixWallLJ1043::precompute(int m)
{
  coeff1[m] = MY_2PI * 2.0 / 5.0 * epsilon[m] * powint(sigma[m], 10);
  coeff2[m] = MY_2PI * epsilon[m] * powint(sigma[m], 4);
  coeff3[m] = MY_2PI * pow(2.0, 1 / 2.0) / 3 * epsilon[m] * powint(sigma[m], 3);
  coeff4[m] = 0.61 / pow(2.0, 1 / 2.0) * sigma[m];
  coeff5[m] = coeff1[m] * 10.0;
  coeff6[m] = coeff2[m] * 4.0;
  coeff7[m] = coeff3[m] * 3.0;

  double rinv = 1.0 / cutoff[m];
  double r2inv = rinv * rinv;
  double r4inv = r2inv * r2inv;
  offset[m] = coeff1[m] * r4inv * r4inv * r2inv - coeff2[m] * r4inv -
      coeff3[m] * powint(cutoff[m] + coeff4[m], -3);
}

/* ---------------------------------------------------------------------- */

void FixWallLJ1043::wall_particle(int m, int which, double coord)
{
  double delta, rinv, r2inv, r4inv, r10inv, 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;

  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 <= 0.0) continue;
      if (delta > cutoff[m]) continue;
      rinv = 1.0 / delta;
      r2inv = rinv * rinv;
      r4inv = r2inv * r2inv;
      r10inv = r4inv * r4inv * r2inv;

      fwall = side *
          (coeff5[m] * r10inv * rinv - coeff6[m] * r4inv * rinv -
           coeff7[m] * powint(delta + coeff4[m], -4));
      f[i][dim] -= fwall;
      ewall[0] += coeff1[m] * r10inv - coeff2[m] * r4inv -
          coeff3[m] * powint(delta + coeff4[m], -3) - offset[m];
      ewall[m + 1] += fwall;

      if (evflag) {
        if (side < 0)
          vn = -fwall * delta;
        else
          vn = fwall * delta;
        v_tally(dim, i, vn);
      }
    }
}