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### fix wall/lj93 command

Syntax:

    fix ID group-ID wall/lj93 style coord epsilon sigma cutoff

- ID, group-ID are documented in fix command
- wall/lj93 = style name of this fix command
- style = xlo or xhi or ylo or yhi or zlo or zhi
- coord = position of wall
- epsilon = Lennard-Jones epsilon for wall-particle interaction
- sigma = Lennard-Jones sigma for wall-particle interaction
- cutoff = distance from wall at which wall-particle interaction is cut off

Examples:

    fix wallhi all wall/lj93 xhi 10.0 1.0 1.0 2.5

Description:

Bound the simulation domain with a Lennard-Jones wall that encloses the atoms. The energy E of a wall-particle interactions is given by the 9-3 potential

where r is the distance from the particle to the wall coord, and epsilon and sigma are the usual LJ parameters. Rc is the cutoff value specified in the command. This interaction is derived by integrating over a 3d half-lattice of Lennard-Jones 12-6 particles. A harder, more repulsive wall interaction can be computed by using the fix wall/lj126 command.

The wall potential is shifted so that the energy of a wall-particle interaction is 0.0 at the cutoff distance.

Restart, fix_modify, output, run start/stop, minimize info:

No information about this fix is written to binary restart files.

The fix_modify energy option is supported by this fix to add the energy of interaction between atoms and the wall to the system's potential energy as part of thermodynamic output.

This fix computes a scalar energy and a 3-vector of forces (on the wall), which can be accessed by various output commands.

No parameter of this fix can be used with the start/stop keywords of the run command.

The forces due to this fix are imposed during an energy minimization, invoked by the minimize command.

IMPORTANT NOTE: If you want the atom/wall interaction energy to be included in the total potential energy of the system (the quantity being minimized), you MUST enable the fix_modify energy option for this fix.

Restrictions:

Any dimension (xyz) that has a LJ 9/3 wall must be non-periodic.

Related commands:

fix wall/reflect, fix wall/lj126

Default: none