Merge pull request #1640 from akohlmey/fix-wall-morse

"wall/lj1043"_fix_wall.html,

"wall/lj126"_fix_wall.html,

"wall/lj93 (k)"_fix_wall.html,

"wall/morse"_fix_wall.html,

"wall/piston"_fix_wall_piston.html,

"wall/reflect (k)"_fix_wall_reflect.html,

"wall/region"_fix_wall_region.html,

"fix wall/lj126"_fix_wall.html - flat walls, with Lennard-Jones 12/6 potential

"fix wall/colloid"_fix_wall.html - flat walls, with "pair_style colloid"_pair_colloid.html potential

"fix wall/harmonic"_fix_wall.html - flat walls, with repulsive harmonic spring potential

"fix wall/morse"_fix_wall.html - flat walls, with Morse potential

"fix wall/region"_fix_wall_region.html - use region surface as wall

"fix wall/gran"_fix_wall_gran.html - flat or curved walls with "pair_style granular"_pair_gran.html potential :ul

The {lj93}, {lj126}, {colloid}, and {harmonic} styles all allow the

flat walls to move with a constant velocity, or oscillate in time.

The "fix wall/region"_fix_wall_region.html command offers the most

generality, since the region surface is treated as a wall, and the

geometry of the region can be a simple primitive volume (e.g. a

The {lj93}, {lj126}, {colloid}, {harmonic}, and {morse} styles all

allow the flat walls to move with a constant velocity, or oscillate in

time.  The "fix wall/region"_fix_wall_region.html command offers the

most generality, since the region surface is treated as a wall, and

the geometry of the region can be a simple primitive volume (e.g. a

sphere, or cube, or plane), or a complex volume made from the union

and intersection of primitive volumes.  "Regions"_region.html can also

specify a volume "interior" or "exterior" to the specified primitive

"wall/lj1043"_fix_wall.html - Lennard-Jones 10-4-3 wall

"wall/lj126"_fix_wall.html - Lennard-Jones 12-6 wall

"wall/lj93"_fix_wall.html - Lennard-Jones 9-3 wall

"wall/morse"_fix_wall.html - Morse potential wall

"wall/piston"_fix_wall_piston.html - moving reflective piston wall

"wall/reflect"_fix_wall_reflect.html - reflecting wall(s)

"wall/region"_fix_wall_region.html - use region surface as wall

fix wall/lj1043 command :h3

fix wall/colloid command :h3

fix wall/harmonic command :h3

fix wall/morse command :h3

[Syntax:]

fix ID group-ID style face args ... keyword value ... :pre

ID, group-ID are documented in "fix"_fix.html command :ulb,l

style = {wall/lj93} or {wall/lj126} or {wall/lj1043} or {wall/colloid} or {wall/harmonic} :l

style = {wall/lj93} or {wall/lj126} or {wall/lj1043} or {wall/colloid} or {wall/harmonic} or {wall/morse} :l

one or more face/arg pairs may be appended :l

face = {xlo} or {xhi} or {ylo} or {yhi} or {zlo} or {zhi} :l

  args for styles {lj93} or {lj126} or {lj1043} or {colloid} or {harmonic} :l

    args = coord epsilon sigma cutoff

    coord = position of wall = EDGE or constant or variable

      EDGE = current lo or hi edge of simulation box

    sigma = size factor for wall-particle interaction (distance units)

      sigma can be a variable (see below)

    cutoff = distance from wall at which wall-particle interaction is cut off (distance units) :pre

  args for style {morse} :l

    args = coord D_0 alpha r_0 cutoff

    coord = position of wall = EDGE or constant or variable

      EDGE = current lo or hi edge of simulation box

      constant = number like 0.0 or -30.0 (distance units)

      variable = "equal-style variable"_variable.html like v_x or v_wiggle

    D_0 = depth of the potential (energy units)

      D_0 can be a variable (see below)

    alpha = width factor for wall-particle interaction (1/distance units)

      alpha can be a variable (see below)

    r_0 = distance of the potential minimum from the face of region (distance units)

      r_0 can be a variable (see below)

    cutoff = distance from wall at which wall-particle interaction is cut off (distance units) :pre

zero or more keyword/value pairs may be appended :l

keyword = {units} or {fld} :l

  {units} value = {lattice} or {box}

fix wallhi all wall/lj93 xlo -1.0 1.0 1.0 2.5 units box

fix wallhi all wall/lj93 xhi EDGE 1.0 1.0 2.5

fix wallhi all wall/morse xhi EDGE 1.0 1.0 1.0 2.5 units box

fix wallhi all wall/lj126 v_wiggle 23.2 1.0 1.0 2.5

fix zwalls all wall/colloid zlo 0.0 1.0 1.0 0.858 zhi 40.0 1.0 1.0 0.858 :pre

:c,image(Eqs/fix_wall_harmonic.jpg)

For style {wall/morse}, the energy E is given by a Morse potential:

:c,image(Eqs/pair_morse.jpg)

In all cases, {r} is the distance from the particle to the wall at

position {coord}, and Rc is the {cutoff} distance at which the

particle and wall no longer interact.  The energy of the wall

spring is at the {cutoff}.  This is a repulsive-only spring since the

interaction is truncated at the {cutoff}

For any wall, the {epsilon} and/or {sigma} parameter can be specified

For the {wall/morse} style, the three parameters are in this order:

{D_0} the depth of the potential, {alpha} the width parameter, and

{r_0} the location of the minimum.  {D_0} has energy units, {alpha}

inverse distance units, and {r_0} distance units.

For any wall, the {epsilon} and/or {sigma} and/or {alpha} parameter can

be specified

as an "equal-style variable"_variable.html, in which case it should be

specified as v_name, where name is the variable name.  As with a

variable wall position, the variable is evaluated each timestep and

#include "respa.h"

#include "error.h"

#include "force.h"

#include "utils.h"

using namespace LAMMPS_NS;

using namespace FixConst;

        estyle[nwall] = CONSTANT;

      }

      if (utils::strmatch(style,"^wall/morse")) {

        if (strstr(arg[iarg+3],"v_") == arg[iarg+3]) {

          int n = strlen(&arg[iarg+3][2]) + 1;

          astr[nwall] = new char[n];

          strcpy(astr[nwall],&arg[iarg+3][2]);

          astyle[nwall] = VARIABLE;

        } else {

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

          astyle[nwall] = CONSTANT;

        }

        ++iarg;

      }

      if (strstr(arg[iarg+3],"v_") == arg[iarg+3]) {

        int n = strlen(&arg[iarg+3][2]) + 1;

        sstr[nwall] = new char[n];