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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.

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

#include "fix_wall_reflect_stochastic.h"

#include <cstring>

#include <cstdlib>

#include "atom.h"

#include "comm.h"

#include "update.h"

#include "modify.h"

#include "domain.h"

#include "lattice.h"

#include "input.h"

#include "variable.h"

#include "error.h"

#include "force.h"

#include "random_mars.h"

using namespace LAMMPS_NS;

using namespace FixConst;

enum{NONE=0,DIFFUSIVE=1,MAXWELL=2,CERCIGNANILAMPIS=3};

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

FixWallReflectStochastic::FixWallReflectStochastic(LAMMPS *lmp, int narg, char **arg) :

  FixWallReflect(lmp, narg, arg), random(NULL)

{

  int arginc,dir;

  if (narg < 8) error->all(FLERR,"Illegal fix wall/reflect/stochastic command");

  if (domain->triclinic != 0) error->all(FLERR, "This fix wall/reflect/stochastic is not incompatible with triclinic simulation box");

  dynamic_group_allow = 1;

  // parse args

  nwall = 0;

  int scaleflag = 1;

  reflectionstyle = NONE;

  if (strcmp(arg[3],"diffusive") == 0) {

    reflectionstyle = DIFFUSIVE;

    arginc = 6;

  } else if (strcmp(arg[3],"maxwell") == 0) {

    reflectionstyle = MAXWELL;

    arginc = 7;

  } else if (strcmp(arg[3],"cercignanilampis") == 0) {

    reflectionstyle = CERCIGNANILAMPIS;

    arginc = 9;

  } else error->all(FLERR,"Illegal fix wall/reflect/stochastic command");

    seedfix = force->inumeric(FLERR,arg[4]);

    if (seedfix <=0) error->all(FLERR,"Random seed must be a postive number");

    random = new RanMars(lmp,seedfix + comm->me);

    int iarg = 5;

    while (iarg < narg) {

      if ((strcmp(arg[iarg],"xlo") == 0) || (strcmp(arg[iarg],"xhi") == 0) ||

          (strcmp(arg[iarg],"ylo") == 0) || (strcmp(arg[iarg],"yhi") == 0) ||

          (strcmp(arg[iarg],"zlo") == 0) || (strcmp(arg[iarg],"zhi") == 0)) {

        if (iarg+2 > narg) error->all(FLERR,"Illegal fix wall/reflect/stochastic command");

        int newwall;

        if (strcmp(arg[iarg],"xlo") == 0) newwall = XLO;

        else if (strcmp(arg[iarg],"xhi") == 0) newwall = XHI;

        else if (strcmp(arg[iarg],"ylo") == 0) newwall = YLO;

        else if (strcmp(arg[iarg],"yhi") == 0) newwall = YHI;

        else if (strcmp(arg[iarg],"zlo") == 0) newwall = ZLO;

        else if (strcmp(arg[iarg],"zhi") == 0) newwall = ZHI;

        for (int m = 0; (m < nwall) && (m < 6); m++)

          if (newwall == wallwhich[m])

            error->all(FLERR,"Wall defined twice in fix wall/reflect/stochastic command");

        wallwhich[nwall] = newwall;

        if (strcmp(arg[iarg+1],"EDGE") == 0) {

          wallstyle[nwall] = EDGE;

          int dim = wallwhich[nwall] / 2;

          int side = wallwhich[nwall] % 2;

          if (side == 0) coord0[nwall] = domain->boxlo[dim];

          else coord0[nwall] = domain->boxhi[dim];

        } else {

          wallstyle[nwall] = CONSTANT;

          coord0[nwall] = force->numeric(FLERR,arg[iarg+1]);

        }

        walltemp[nwall]= force->numeric(FLERR,arg[iarg+2]);

        for (dir = 0; dir < 3; dir++) {

          wallvel[nwall][dir]= force->numeric(FLERR,arg[iarg+dir+3]);

          int dim = wallwhich[nwall] / 2;

          if ((wallvel[nwall][dir] !=0) & (dir == dim)) error->all(FLERR,"The wall velocity must be tangential");

          if (reflectionstyle == CERCIGNANILAMPIS) {

            wallaccom[nwall][dir]= force->numeric(FLERR,arg[iarg+dir+6]);

          } else if (reflectionstyle == MAXWELL) {

            wallaccom[nwall][dir]= force->numeric(FLERR,arg[iarg+6]);// One accommodation coefficient for all directions

          }

        }

        nwall++;

        iarg += arginc;

      } else if (strcmp(arg[iarg],"units") == 0) {

        if (iarg+2 > narg) error->all(FLERR,"Illegal wall/reflect/stochastic command");

        if (strcmp(arg[iarg+1],"box") == 0) scaleflag = 0;

        else if (strcmp(arg[iarg+1],"lattice") == 0) scaleflag = 1;

        else error->all(FLERR,"Illegal fix wall/reflect/stochastic command");

        iarg += 2;

      } else error->all(FLERR,"Illegal fix wall/reflect/stochastic command");

    }

    // error check

    if (nwall == 0) error->all(FLERR,"Illegal fix wall command");

    for (int m = 0; m < nwall; m++) {

      if ((wallwhich[m] == XLO || wallwhich[m] == XHI) && domain->xperiodic)

        error->all(FLERR,"Cannot use fix wall/reflect/stochastic in periodic dimension");

      if ((wallwhich[m] == YLO || wallwhich[m] == YHI) && domain->yperiodic)

        error->all(FLERR,"Cannot use fix wall/reflect/stochastic in periodic dimension");

      if ((wallwhich[m] == ZLO || wallwhich[m] == ZHI) && domain->zperiodic)

        error->all(FLERR,"Cannot use fix wall/reflect/stochastic in periodic dimension");

    }

    for (int m = 0; m < nwall; m++)

      if ((wallwhich[m] == ZLO || wallwhich[m] == ZHI) && domain->dimension == 2)

        error->all(FLERR,

                   "Cannot use fix wall/reflect/stochastic zlo/zhi for a 2d simulation");

    // scale factors for CONSTANT walls, VARIABLE wall is not allowed

    int flag = 0;

    for (int m = 0; m < nwall; m++)

      if (wallstyle[m] != EDGE) flag = 1;

    if (flag) {

      if (scaleflag) {

        xscale = domain->lattice->xlattice;

        yscale = domain->lattice->ylattice;

        zscale = domain->lattice->zlattice;

      }

      else xscale = yscale = zscale = 1.0;

      for (int m = 0; m < nwall; m++) {

        if (wallstyle[m] != CONSTANT) continue;

        if (wallwhich[m] < YLO) coord0[m] *= xscale;

        else if (wallwhich[m] < ZLO) coord0[m] *= yscale;

        else coord0[m] *= zscale;

      }

    }

  }

FixWallReflectStochastic::~FixWallReflectStochastic()

{

delete random ;

}

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

void FixWallReflectStochastic::wall_particle(int m, int which, double coord)

{

  int i, dir, dim, side, sign;

  double vsave,factor,timecol,difftest,theta;

  double *rmass;

  double *mass = atom->mass;

  // coord = current position of wall

  // evaluate variable if necessary, wrap with clear/add

  double **x = atom->x;

  double **v = atom->v;

  int *mask = atom->mask;

  int *type = atom->type;

  int nlocal = atom->nlocal;

  dim = which / 2;

  side = which % 2;

  for (i = 0; i < nlocal; i++) {

    if (mask[i] & groupbit) {

      sign = 0;

      if ((side == 0) & (x[i][dim] < coord)){

        sign = 1;

      } else if ((side == 1) & (x[i][dim] > coord)){

        sign = -1;

      }

      if (sign != 0) {

        if (rmass) theta = force->boltz*walltemp[m]/(rmass[i]*force->mvv2e);// theta = kT/m

        else theta = force->boltz*walltemp[m]/(mass[type[i]]*force->mvv2e);

        factor = sqrt(theta);

        timecol= (x[i][dim] - coord)/v[i][dim]; // time travelling after collision

        if (reflectionstyle  == MAXWELL) {difftest = random->uniform(); }// for Maxwell model only

        for (dir = 0; dir < 3; dir++) {

          x[i][dir] -= v[i][dir]*timecol; // pushing back atoms to the wall position and assign new reflected velocity

          // Diffusive reflection

          if (reflectionstyle  == DIFFUSIVE){

            if (dir != dim) {

              v[i][dir] = wallvel[m][dir] + random->gaussian(0,factor);

            } else { v[i][dir] =  sign*random->rayleigh(factor) ; }

          }

          // Maxwell reflection

          if (reflectionstyle  == MAXWELL){

            if (difftest < wallaccom[m][dir]) {

              if (dir != dim) {

                v[i][dir] = wallvel[m][dir] + random->gaussian(0,factor);

              } else { v[i][dir] =  sign*random->rayleigh(factor) ; }

            } else {

              if (dir == dim) {v[i][dir] = -v[i][dir];

              }

            }

          }

          // Cercignani Lampis reflection

          if (reflectionstyle  == CERCIGNANILAMPIS){

            if (dir != dim) {

              v[i][dir] = wallvel[m][dir] + random->gaussian((1-wallaccom[m][dir])*(v[i][dir]-wallvel[m][dir]),sqrt((2-wallaccom[m][dir])*wallaccom[m][dir]*theta)) ;

            } else { v[i][dir] = random->besselexp(theta, wallaccom[m][dir], v[i][dir]) ; }

          }

          // update new position due to the new velocity

          if (dir != dim) {

            x[i][dir] += v[i][dir]*timecol; }

          else {x[i][dir] = coord + v[i][dir]*timecol;}

        }// for loop

      }// if sign

    }// if mask

  }

}

 No newline at end of file

/* -*- c++ -*- ----------------------------------------------------------

   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.

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

#ifdef FIX_CLASS

FixStyle(wall/reflect/stochastic,FixWallReflectStochastic)

#else

#ifndef LMP_FIX_WALL_REFLECT_STOCHASTIC_H

#define LMP_FIX_WALL_REFLECT_STOCHASTIC_H

#include "random_mars.h"

#include "fix_wall_reflect.h"

namespace LAMMPS_NS {

class FixWallReflectStochastic : public FixWallReflect {

 public:

  FixWallReflectStochastic(class LAMMPS *, int, char **);

  void wall_particle(int m,int which, double coord);

  virtual ~FixWallReflectStochastic();

 protected:

    class RanMars *random;

    int seedfix;

    double walltemp[6],wallvel[6][3],wallaccom[6][3];

    int reflectionstyle;

};

}

#endif

#endif

/* ERROR/WARNING messages:

E: Illegal ... command

Self-explanatory.  Check the input script syntax and compare to the

documentation for the command.  You can use -echo screen as a

command-line option when running LAMMPS to see the offending line.

E: Wall defined twice in fix wall/stochastic command

Self-explanatory.

E: Cannot use fix wall/stochastic in periodic dimension

Self-explanatory.

E: Cannot use fix wall/stochastic zlo/zhi for a 2d simulation

Self-explanatory.

E: Variable name for fix wall/stochastic does not exist

Self-explanatory.

E: Variable for fix wall/stochastic is invalid style

Only equal-style variables can be used.

W: Should not allow rigid bodies to bounce off relecting walls

LAMMPS allows this, but their dynamics are not computed correctly.

*/