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bond_coeff command

Syntax:

bond_coeff N args 

Examples:

bond_coeff 5 80.0 1.2
bond_coeff * 30.0 1.5 1.0 1.0
bond_coeff 1*4 30.0 1.5 1.0 1.0
bond_coeff 1 harmonic 200.0 1.0 

Description:

Specify the force field coefficients for one or more bond types. The number and meaning of the coefficients depends on the bond style. As described below, bond 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 bond types. This takes the form "*" or "*n" or "n*" or "m*n". If N = the number of bond 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 bond_coeff commands for the same bond type is perfectly valid. For example, these commands set the coeffs for all bond types, then overwrite the coeffs for just bond type 2:

bond_coeff * 100.0 1.2
bond_coeff 2 200.0 1.2 

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

5 80.0 1.2 

The units of each coefficient are shown in parenthesis.


For style class2, specify 4 coefficients:


For style fene, specify 4 coefficients:


For style fene/expand, specify 5 coefficients:


For style harmonic, specify 2 coefficients:


For style morse, specify 3 coefficients:


For style nonlinear, specify 3 coefficients:


For style hybrid, the first coefficient sets the bond style and the remaining coefficients are those appropriate to that style. For example, these commands:

bond_coeff 1 fene 30.0 1.5 1.0 1.0
bond_coeff 2 harmonic 80.0 1.2 

would set bonds of bond type 1 to be computed with a fene potential with coefficients 30.0, 1.5, 1.0, 1.0 for K, R0, epsilon, sigma. Likewise, bonds of bond type 2 would be computed with a harmonic potential with coefficients 80.0, 1.2 for K, r0.

Restrictions:

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

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

Related commands:

bond_style

Default: none