ELPH WF CACHE MB
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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
⟨ψnk|ΔVq|ψmk′⟩,
where k′ = k + q. Because k-points are distributed across MPI ranks, the wavefunction ψnk 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.