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fix wall/ees command

fix wall/region/ees command

Syntax:

fix ID group-ID style args 

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

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:

Introduced by Babadi and Ejtehadi in (Babadi). 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:

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 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 doc page for more info.

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

Related commands:

fix wall, pair resquared

Default:

none


(Babadi) Babadi and Ejtehadi, EPL, 77 (2007) 23002.