dihedral_style hybrid command

Syntax

dihedral_style hybrid style1 style2 ...
  • style1,style2 = list of one or more dihedral styles

Examples

dihedral_style hybrid harmonic helix
dihedral_coeff 1 harmonic 6.0 1 3
dihedral_coeff 2* helix 10 10 10

Description

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

In the dihedral_coeff commands, the name of a dihedral style must be added after the dihedral type, with the remaining coefficients being those appropriate to that style. In the example above, the 2 dihedral_coeff commands set dihedrals of dihedral type 1 to be computed with a harmonic potential with coefficients 6.0, 1, 3 for K, d, n. All other dihedral types (2-N) are computed with a helix potential with coefficients 10, 10, 10 for A, B, C.

If dihedral coefficients are specified in the data file read via the read_data command, then the same rule applies. E.g. “harmonic” or “helix”, must be added after the dihedral type, for each line in the “Dihedral Coeffs” section, e.g.

Dihedral Coeffs

1 harmonic 6.0 1 3
2 helix 10 10 10
...

If class2 is one of the dihedral hybrid styles, the same rule holds for specifying additional AngleTorsion (and EndBondTorsion, etc) coefficients either via the input script or in the data file. I.e. class2 must be added to each line after the dihedral type. For lines in the AngleTorsion (or EndBondTorsion, etc) section of the data file for dihedral types that are not class2, you must use an dihedral style of skip as a placeholder, e.g.

AngleTorsion Coeffs

1 skip
2 class2 1.0 1.0 1.0 3.0 3.0 3.0 30.0 50.0
...

Note that it is not necessary to use the dihedral style skip in the input script, since AngleTorsion (or EndBondTorsion, etc) coefficients need not be specified at all for dihedral types that are not class2.

A dihedral style of none with no additional coefficients can be used in place of a dihedral style, either in a input script dihedral_coeff command or in the data file, if you desire to turn off interactions for specific dihedral types.


Restrictions

This dihedral style can only be used if LAMMPS was built with the MOLECULE package. See the Making LAMMPS section for more info on packages.

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