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fix wall/lj126 command

Syntax:

fix ID group-ID wall/lj126 style coord epsilon sigma cutoff keyword values ... 

Examples:

fix wallhi all wall/lj126 xhi 10.0 1.0 1.0 1.12
fix leftwall all wall/lj126 zlo 0.0  1.0 1.0 0.858 vel 1.0 

Description:

Bound the simulation domain on one of its faces with a Lennard-Jones wall that interacts with the atoms in the group. The energy E of wall-particle interactions is given by the 12-6 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 provides a harder, more repulsive interaction with the wall than the softer 9-3 potential provided by the fix wall/lj93 command.

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

If the vel keyword is specified, the position of wall will move during the simulation, based on its initial position (coord), the specified velocity (vel), and the time elapsed since the beginning of the simulation. Xlo or xhi walls move in the x direction with whatever sign you give the v argument. Ditto for y and z walls. See the note below about making the wall move continuously across multiple runs.

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. The scalar and vector values calculated by this fix are "extensive", meaning they scale with the number of atoms in the simulation.

This fix can change the position of the wall, due to the vel keyword, continuously over multiple runs, using the start and stop keywords of the run command. If you do not do this, the wall position will be reset to coord at the beginning of each run.

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 12/6 wall must be non-periodic.

Related commands:

fix wall/reflect, fix wall/lj93

Default:

The option defaults are vel = 0.