vaspelph.h5

The vaspelph.h5 file contains electron-phonon matrix elements and related quantities. It is created when ELPH_DRIVER = mels.

Warning: Within the projector-augmented-wave method, different definitions of the electron-phonon matrix element exist. In order to choose which one is used and written to vaspelph.h5, please use the ELPH_DECOMPOSE tag.

Mind: Available as of VASP 6.5.0

It is usually best to avoid writing the electron-phonon matrix elements to disk. There are several reasons for this:

The total number of matrix elements required for a particular electron-phonon calculation can be very large, thus requiring a lot of disk space.
Writing to or reading from the hard drive is usually much slower than keeping data in memory. This can cause a performance bottleneck in your calculation. This is especially true on distributed clusters where additional communication is required.
When running electron-phonon calculations directly inside VASP, it is possible to avoid calculating some matrix elements. For example, during transport calculations, only the matrix elements close to the chemical potential have sizeable contributions. The ones further away are not calculated by default, which can give a significant performance boost. This advantage is lost when choosing to write the matrix elements to disk.

However, the information in the vaspelph.h5 file is still useful in some situations. For example, ELPH_DRIVER = mels can be used to plot the electron-phonon matrix along high-symmetry lines or for specific combinations of bands, modes and k/q-points.

Related tags and articles