compute_phonon
This keyword can be used to compute the phonon dispersions using the finite-displacement method. The results are written to the D.out output file and the omega2.out output file.
To use this keyword, please make sure the following files have been preprared in the input directory:
Input filename |
Brief description |
|---|---|
|
Define the mapping from the atom label to the basis label |
|
Specify the \(\boldsymbol{k}\)-points |
Syntax
This keyword is used as follows:
compute_phonon <cutoff> <displacement>
cutoff is the cutoff distance (in units of Å) for calculating the force constants.
displacement is the displacement (in units of Å) for calculating the force constants using the finite-displacement method.
Example
For example, the command:
compute_phonon 5.0 0.01
means that one wants to compute the phonon dispersion using a cutoff distance of 5 Å and a displacement of 0.01 Å.
Caveats
This keyword should occur after all the potential keywords.
For two-body potentials, the cutoff distance for force constants can be the same as that for force evaluations. However, for many-body potentials, the cutoff distance for force constants usually needs to be twice of the potential cutoff distance. Also make sure that the box size in any direction is at least twice of this force constant cutoff distance.