improper_style hybrid command

Syntax

improper_style hybrid style1 style2 ...
  • style1,style2 = list of one or more improper styles

Examples

improper_style hybrid harmonic helix
improper_coeff 1 harmonic 120.0 30
improper_coeff 2 cvff 20.0 -1 2

Description

The hybrid style enables the use of multiple improper styles in one simulation. An improper style is assigned to each improper type. For example, impropers in a polymer flow (of improper type 1) could be computed with a harmonic potential and impropers in the wall boundary (of improper type 2) could be computed with a cvff potential. The assignment of improper type to style is made via the improper_coeff command or in the data file.

In the improper_coeff command, the first coefficient sets the improper style and the remaining coefficients are those appropriate to that style. In the example above, the 2 improper_coeff commands would set impropers of improper type 1 to be computed with a harmonic potential with coefficients 120.0, 30 for K, X0. Improper type 2 would be computed with a cvff potential with coefficients 20.0, -1, 2 for K, d, n.

If the improper class2 potential is one of the hybrid styles, it requires additional AngleAngle coefficients be specified in the data file. These lines must also have an additional “class2” argument added after the improper type. For improper types which are assigned to other hybrid styles, use the style name (e.g. “harmonic”) appropriate to that style. The AngleAngle coeffs for that improper type will then be ignored.

An improper style of none can be specified as the 2nd argument to the improper_coeff command, if you desire to turn off certain improper types.

Restrictions

This improper style can only be used if LAMMPS was built with the MOLECULE package (which it is by default). See the Making LAMMPS section for more info on packages.

Unlike other improper styles, the hybrid improper style does not store improper coefficient info for individual sub-styles in a binary restart files. Thus when retarting a simulation from a restart file, you need to re-specify improper_coeff commands.