improper_style distharm command
improper_style distharm improper_coeff 1 25.0 0.5
The distharm improper style uses the potential
where d is the oriented 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 distance d is oriented and can take on negative values. This may lead to unwanted behavior if d0 is not equal to zero.
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:
This improper style can only be used if LAMMPS was built with the USER-YAFF package. See the Build package doc page for more info.