Keywords: user_guide

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# 1 Introduction

This guide covers the usage of the `PHonon` package, a part of the QUANTUM ESPRESSO distribution. Further documentation, beyond what is provided in this guide, can be found in the directory `PHonon/Doc/`, containing a copy of this guide.

Important notice: due to the lack of time and of manpower, this manual is only partially updated and may contain outdated information.

This guide assumes that you know the contents of the general User's Guide for QUANTUM ESPRESSO and of the User's Guide for `PWscf`. It also assumes that you have already installed QUANTUM ESPRESSO (`PHonon` is not a stand-alone package: it requires `PWscf` to be compiled and used). If not, please locate the general User's Guide in directory `Doc/` two levels above the one containing this guide, and the User's Guide for `PWscf` in `PW/Doc/`; or consult the web site:
`http://www.quantum-espresso.org`. It is also assumed that you know the physics behind QUANTUM ESPRESSO, the methods it implements, and in particular the physics and the methods of `PHonon`.

`PHonon` has the following directory structure, contained in a subdirectory `PHonon/` of the main QUANTUM ESPRESSO tree:

`Doc/` | : contains the user_guide and input data description
`examples/` | : some running examples
`PH/` | : source files for phonon calculations and analysis
`Gamma/` | : source files for Gamma-only phonon calculation

Important Notice: since v.5.4, many modules and routines that were common to all linear-response QUANTUM ESPRESSO codes are moved into the new `LR_Modules` subdirectory of the main tree. Since v.6.0, the `D3` code for anharmonic force constant calculations has been superseded by the `D3Q` coda, available on `http://www.qe-forge.org/gf/project/d3q/`.

The codes available in the `PHonon` package can perform the following types of calculations:

- phonon frequencies and eigenvectors at a generic wave vector, using Density-Functional Perturbation Theory;
- effective charges and dielectric tensors;
- electron-phonon interaction coefficients for metals;
- interatomic force constants in real space;
- Infrared and Raman (nonresonant) cross section.

Phonons can be plotted using the `PlotPhon` package. Calculations of the vibrational free energy in the Quasi-Harmonic approximations can be performed using the `QHA` package. Note: since v.5.4, these two packages are separately distributed and no longer bundled with `PHonon`. Their latest version can be found in the tarballs of `PHonon` v.5.3.

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