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improper_style class2 command

Syntax:

improper_style class2 

Examples:

improper_style class2
improper_coeff 1 100.0 0 

Description:

The class2 improper style uses the potential

where Ei is the improper term and Eaa is an angle-angle term. The chi used in Ei is an average over 3 possible chi orientations. The subscripts on the various theta's refer to different combinations of atoms i,j,k,l used to form the angle; theta1, theta2, theta3 are the equilibrium positions of those angles.

See (Sun) for a description of the COMPASS class2 force field.

The following coefficients must be defined for each improper type via the improper_coeff command as in the example above, or in the data file or restart files read by the read_data or read_restart commands:

For this style, 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.

Restrictions:

This improper style is part of the "class2" package. It is only enabled if LAMMPS was built with that package. See the Making LAMMPS section for more info.

Related commands:

improper_coeff

Default: none


(Sun) Sun, J Phys Chem B 102, 7338-7364 (1998).