phonon

phonon <key1> <args1...> <key2> <args2...> ...

**Note:** only available in calculations using the 'phonon' executable.

Control phonon calculation and output. The possible <key>'s and their corresponding arguments are:

supercell <N0> <N1> <N2>

Supercell for frozen phonon perturbation. Each entry must divide the corresponding value in kpoint-folding. The k-point mesh must be uniform and centered on Gamma.

dr <dr>

Amplitude (in bohrs) of frozen phonon perturbation (default 0.1).

iPerturbation <iPert>

Only run supercell calculation for perturbation number <iPert> (1-based). Use the dry run to list out the number of perturbations, and the nStates for each so that they can each be run individually with the optimum MPI configuration. Use collectPerturbations below after all iPerturbation calculations complete.

collectPerturbations

Collect results of previous individual supercell calculations. Note that this requires all iPerturbation calculations (listed at the end of the phonon dry run) to have already completed.

saveHsub yes|no

Whether to compute / save phononHsub: the electron-phonon matrix elements. Default: yes.

useVPT

Compute perturbations using variational perturbation theory (VPT) instead of finite differencing. Finite difference with step size dr is still used to calculate second derivative of energy. Set dr to 0 to compute analytically instead (only for non-ultrasoft potentials, and slightly slower.)

T <T>

Temperature (in Kelvins) used for vibrational free energy estimation (default 298).

Fcut <Fcut>

Fillings threshold to include in supercell calculation (default 1e-8). The unit cell calculation may have extra bands for which matrix elements are desired; this flag ensures that those extra bands do not affect the performance or memory requirements of the supercell calculations.

rSmooth <rSmooth>

Width in bohrs of the supercell boundary region over which matrix elements are smoothed.

**Requires:** (None)

**Forbids:** fix-electron-density fix-electron-potential

**Allow multiple:** no

**Default:** (None)

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