"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)

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fix wall/ees command :h3
fix wall/region/ees command :h3

[Syntax:]

fix ID group-ID style args :pre

ID, group-ID are documented in "fix"_fix.html command :ulb,l
style = {wall/ees} or {wall/region/ees} :l
  args for style {wall/ees}: one or more {face parameters} groups may be appended
  face = {xlo} or {xhi} or {ylo} or {yhi} or {zlo} or {zhi}
  parameters = coord epsilon sigma 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
    epsilon = strength factor for wall-particle interaction (energy or energy/distance^2 units)
      epsilon can be a variable (see below)
    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 {wall/region/ees}: {region-ID} {epsilon} {sigma} {cutoff}
    region-ID = region whose boundary will act as wall
    epsilon = strength factor for wall-particle interaction (energy or energy/distance^2 units)
    sigma = size factor for wall-particle interaction (distance units)
    cutoff = distance from wall at which wall-particle interaction is cut off (distance units) :pre
  :ule

[Examples:]

fix wallhi all wall/ees xlo -1.0 1.0 1.0 2.5 units box
fix wallhi all wall/ees xhi EDGE 1.0 1.0 2.5
fix wallhi all wall/ees v_wiggle 23.2 1.0 1.0 2.5
fix zwalls all wall/ees zlo 0.0 1.0 1.0 0.858 zhi 40.0 1.0 1.0 0.858 :pre

fix ees_cube all wall/region/ees myCube 1.0 1.0 2.5 :pre


[Description:]

Fix {wall/ees} bounds the simulation domain on one or more of its
faces with a flat wall that interacts with the ellipsoidal atoms in the
group by generating a force on the atom in a direction perpendicular to
the wall and a torque parallel with the wall.  The energy of
wall-particle interactions E is given by:

:c,image(Eqs/fix_wall_ees.jpg)

Introduced by Babadi and Ejtehadi in "(Babadi)"_#BabadiEjtehadi. Here,
{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. Also, sigma_n is the distance between center of
ellipsoid and the nearest point of its surface to the wall. The energy
of the wall is:

:c,image(JPG/fix_wall_ees_image.jpg)

Details of using this command and specifications are the same as
fix/wall command. You can also find an example in USER/ees/ under
examples/ directory.

The prefactor {epsilon} can be thought of as an
effective Hamaker constant with energy units for the strength of the
ellipsoid-wall interaction.  More specifically, the {epsilon} pre-factor
= 8 * pi^2 * rho_wall * rho_ellipsoid * epsilon
* sigma_a * sigma_b * sigma_c, where epsilon is the LJ parameters for
the constituent LJ particles and sigma_a, sigma_b, and sigma_c are radii
of ellipsoidal particles. Rho_wall and rho_ellipsoid are the number
density of the constituent particles, in the wall and ellipsoid
respectively, in units of 1/volume.

NOTE: You must insure that r is always bigger than sigma_n for
all particles in the group, or LAMMPS will generate an error.  This
means you cannot start your simulation with particles touching the wall
position {coord} (r = sigma_n) or with particles penetrating the wall
(0 =< r < sigma_n) or with particles on the wrong side of the
wall (r < 0).


Fix {wall/region/ees} treats the surface of the geometric region defined
by the {region-ID} as a bounding wall which interacts with nearby
ellipsoidal particles according to the EES potential introduced above.

Other details of this command are the same as for the "fix
wall/region"_fix_wall_region.html command.  One may also find an example
of using this fix in the examples/USER/misc/ees/ directory.

[Restrictions:]

This fix is part of the USER-MISC package.  It is only enabled if
LAMMPS was built with that package.  See the "Build
package"_Build_package.html doc page for more info.

This fix requires that atoms be ellipsoids as defined by the
"atom_style ellipsoid"_atom_style.html command.

[Related commands:]

"fix wall"_fix_wall.html,
"pair resquared"_pair_resquared.html

[Default:]

none

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:link(BabadiEjtehadi)
[(Babadi)] Babadi and Ejtehadi, EPL, 77 (2007) 23002.
