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.
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:
Improper styles can only be set for atom styles that allow impropers to be defined.
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:
Default: none