dynamical_matrix group-ID style gamma args keyword value ...
group-ID = ID of group of atoms to displace
style = regular or eskm
gamma = finite different displacement length (distance units)
one or more keyword/arg pairs may be appended
keyword = file or binary file name = name of output file for the dynamical matrix binary arg = yes or no or gzip
dynamical_matrix 1 regular 0.000001 dynamical_matrix 1 eskm 0.000001 dynamical_matrix 3 regular 0.00004 file dynmat.dat dynamical_matrix 5 eskm 0.00000001 file dynamical.dat binary yes
Calculate the dynamical matrix by finite difference of the selected group,
where D is the dynamical matrix and Phi is the force constant matrix defined by
The output for the dynamical matrix is printed three elements at a time. The three elements are the three beta elements for a respective i/alpha/j combination. Each line is printed in order of j increasing first, alpha second, and i last.
If the style eskm is selected, the dynamical matrix will be in units of inverse squared femtoseconds. These units will then conveniently leave frequencies in THz, where frequencies, represented as omega, can be calculated from
The command collects an array of nine times the number of atoms in a group on every single MPI rank, so the memory requirements can be very significant for large systems.
This command is part of the USER-PHONON package. It is only enabled if LAMMPS was built with that package. See the Build package doc page for more info.
The default settings are file = “dynmat.dyn”, binary = no