4 Using PHonon
Keywords: user_guide

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# 4 Using `PHonon`

Phonon calculation is presently a two-step process. First, you have to find the ground-state atomic and electronic configuration; Second, you can calculate phonons using Density-Functional Perturbation Theory. Further processing to calculate Interatomic Force Constants, to add macroscopic electric field and impose Acoustic Sum Rules at = 0 may be needed. In the following, we will indicate by the phonon wavevectors, while will indicate Bloch vectors used for summing over the Brillouin Zone.

The main code `ph.x` can be used whenever `PWscf` can be used, with the exceptions of DFT+U, hybrid functionals, external electric fields, constraints on magnetization, nonperiodic boundary conditions. USPP and PAW are not implemented for higher-order response calculations. See the header of file `PHonon/PH/phonon.f90` for a complete and updated list of what `PHonon` can and cannot do.

Since version 4.0 it is possible to safely stop execution of `ph.x` code using the same mechanism of the `pw.x` code, i.e. by creating a file `prefix.EXIT` in the working directory. Execution can be resumed by setting `recover=.true.` in the subsequent input data. Moreover the execution can be (cleanly) stopped after a given time is elapsed, using variable `max_seconds`. See `example/Recover_example/`.

Subsections

- 4.1 Single-q calculation
- 4.2 Calculation of interatomic force constants in real space
- 4.3 Calculation of electron-phonon interaction coefficients
- 4.4 DFPT with the tetrahedron method
- 4.5 Calculation of electron-phonon interaction coefficients with the tetrahedron method
- 4.6 Phonons for two-dimensional crystals
- 4.7 Phonons from DFPT+U
- 4.8 Fourier interpolation of phonon potential
- 4.9 Calculation of phonon-renormalization of electron bands