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improper_coeff command

Syntax:

improper_coeff N args 

Examples:

improper_coeff 1 300.0 0.0
improper_coeff * 80.2 -1 2
improper_coeff *4 80.2 -1 2 

Description:

Specify the force field coefficients for one or more improper types. The number and meaning of the coefficients depends on the improper style. As described below, improper 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 improper types. This takes the form "*" or "*n" or "n*" or "m*n". If N = the number of improper 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).

Note that using 2 improper_coeff commands for the same improper type is perfectly valid. For example, these commands set the coeffs for all improper types, then overwrite the coeffs for just improper type 2:

improper_coeff * 300.0 0.0
improper_coeff 2 50.0 0.0 

A line in a data file that specifies improper coefficients uses the exact same format as the arguments of the improper_coeff command in an input script, except that wild-card asteriks should not be used since coefficients for all N types are listed in the file. For example, under the "Improper Coeffs" section of a data file, the line that corresponds to the 1st example above would be listed as

1 300.0 0.0 

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


For style class2, only coefficients for the Ei formula can be specified in the input script. These are the 2 coefficients:

X0 is specified in degrees, but LAMMPS converts it to radians internally; hence the units of K are in energy/radian^2.

Coefficients for the Eaa formula must be specified in the data file. For the Eaa formula, the coefficients are listed under a "AngleAngle Coeffs" heading and each line lists 6 coefficients:

The theta values are specified in degrees, but LAMMPS converts them to radians internally; hence the units of M are in energy/radian^2.


For style cvff, specify 3 coefficients:


For style harmonic, specify 2 coefficients:

X0 is specified in degrees, but LAMMPS converts it to radians internally; hence the units of K are in energy/radian^2.

Restrictions:

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

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

Related commands:

improper_style

Default: none