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dihedral_coeff command

Syntax:

dihedral_coeff N args 

Examples:

dihedral_coeff 1 80.0 1 3
dihedral_coeff * 80.0 1 3 0.5
dihedral_coeff 2* 80.0 1 3 0.5 

Description:

Specify the force field coefficients for one or more dihedral types. The number and meaning of the coefficients depends on the dihedral style. Dihedral coefficients can also be set in the data file read by the read_data command or in a restart file.

N can be specified in one of two ways. An explicit numeric value can be used, as in the 1st example above. Or a wild-card asterik can be used to set the coefficients for multiple dihedral types. This takes the form "*" or "*n" or "n*" or "m*n". If N = the number of dihedral types, then an asterik with no numeric values means all types from 1 to N. A leading asterik means all types from 1 to n (inclusive). A trailing asterik means all types from n to N (inclusive). A middle asterik means all types from m to n (inclusive).

A line in a data file that specifies dihedral coefficients uses the exact same format as the arguments of the dihedral_coeff command in an input script, except that no wild-card asterik can be used. For example, under the "Dihedral Coeffs" section of a data file, the line that corresponds to the 1st example above would be listed as

1 80.0 1 3 

See the dihedral_style command for the formulas that use these coefficients. The units of each coefficient are shown in parenthesis.

For style harmonic, specify 3 coefficients:

For style charmm, specify 4 coefficients:

The weighting factor is applied to pairwise interaction between the 1st and 4th atoms in the dihedral.

For style multiharmonic, specify 5 coefficients:

Restrictions:

This command must come after the simulation box is defined by a read_data, read_restart, or create_box command.

An dihedral style must be defined before any dihedral coefficients are set, either in the input script or in a data file.

Related commands:

dihedral_style

Default: none