improper_style distance command
improper_style distance improper_coeff 1 80.0 100.0
The distance 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 I-atom is assumed to be the central atom.
Note that defining 4 atoms to interact in this way, does not mean that bonds necessarily exist between I-J, J-K, or K-L, as they would in a linear dihedral. Normally, the bonds I-J, I-K, I-L would exist for an improper to be defined between the 4 atoms.
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:
- K_2 (energy/distance^2)
- K_4 (energy/distance^4)
This improper style can only be used if LAMMPS was built with the USER-MISC package. See the Making LAMMPS section for more info on packages.