ELPH WF CACHE MB: Difference between revisions
Add ELPH_WF_CACHE_MB tag page: wavefunction cache for electron-phonon MPI communication |
No edit summary |
||
| Line 3: | Line 3: | ||
Description: Maximum memory (in MB) allocated for caching wavefunctions during electron-phonon matrix element calculations. | Description: Maximum memory (in MB) allocated for caching wavefunctions during electron-phonon matrix element calculations. | ||
{{Available|6.5.1}} | {{Available|6.5.1}} | ||
---- | ---- | ||
| Line 12: | Line 11: | ||
A separate cache for the PAW projections is also sized proportionally to <code>ELPH_WF_CACHE_MB</code>. | A separate cache for the PAW projections is also sized proportionally to <code>ELPH_WF_CACHE_MB</code>. | ||
The wavefunction cache works together with <code>ELPH_WF_CACHE_PREFILL</code> (default: <code>.TRUE.</code>), 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. | The wavefunction cache works together with <code>ELPH_WF_CACHE_PREFILL</code> (default: <code>.TRUE.</code>), 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. | ||
Revision as of 12:15, 18 June 2026
Template:DISPLAYTITLE
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.