improper_style sqdistharm command
improper_style sqdistharm improper_coeff 1 50.0 0.1
The sqdistharm improper style uses the potential
where d is the distance between the central atom and the plane formed by the other three atoms. If the 4 atoms in an improper quadruplet (listed in the data file read by the read_data command) are ordered I,J,K,L then the L-atom is assumed to be the central atom. Note that this is different from the convention used in the improper_style distance.
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:
Note that d0^2 (in units distance^2) has be provided and not d0.
This improper style can only be used if LAMMPS was built with the USER-MISC package. See the Build package doc page for more info.