compute_phonon
¶
This keyword can be used to compute the phonon dispersions using the finitedisplacement 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 finitedisplacement 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 twobody potentials, the cutoff distance for force constants can be the same as that for force evaluations. However, for manybody 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.