ELPH_WF_CACHE_MB
ELPH_WF_CACHE_MB = real
Default: ELPH_WF_CACHE_MB = 1000
Description: Maximum memory (in MB) allocated for caching wavefunctions during electron-phonon matrix element calculations.
| Mind: Available as of VASP 6.5.1 |
Electron-phonon matrix elements are sandwiches of the form
- [math]\displaystyle{ \langle \psi_{n\mathbf{k}} | \Delta V_{\mathbf{q}} | \psi_{m\mathbf{k}'} \rangle, }[/math]
where [math]\displaystyle{ \mathbf{k}' = \mathbf{k} + \mathbf{q} }[/math]. Because k-points are distributed across MPI ranks, the wavefunction [math]\displaystyle{ \psi_{n\mathbf{k}} }[/math] needed to form the bra may reside on a different rank than the one computing the matrix element. ELPH_WF_CACHE_MB sets the maximum memory (in megabytes) used to cache these remotely fetched wavefunctions locally, avoiding repeated inter-rank MPI communication.
A separate cache for the PAW projections is also sized proportionally to ELPH_WF_CACHE_MB.
The wavefunction cache works together with ELPH_WF_CACHE_PREFILL (default: .TRUE.), which pre-populates the cache before the main electron-phonon loop begins. When pre-fill succeeds, almost all subsequent wavefunction accesses are served from the cache without MPI communication.