angle_style cross command
angle_style cross angle_coeff 1 200.0 100.0 100.0 1.25 1.25 107.0
The cross angle style uses a potential that couples the bond stretches of a bend with the angle stretch of that bend:
where r12,0 is the rest value of the bond length between atom 1 and 2, r32,0 is the rest value of the bond length between atom 2 and 2, and theta0 is the rest value of the angle. KSS is the force constant of the bond stretch-bond stretch term and KBS0 and KBS1 are the force constants of the bond stretch-angle stretch terms.
The following coefficients must be defined for each angle type via the angle_coeff command as in the example above, or in the data file or restart files read by the read_data or read_restart commands:
Theta0 is specified in degrees, but LAMMPS converts it to radians internally; hence the units of KBS0 and KBS1 are in energy/distance/radian.
This angle style can only be used if LAMMPS was built with the USER_YAFF package. See the Build package doc page for more info.