ELPH WF CACHE MB: Difference between revisions
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Add ELPH_WF_CACHE_MB tag page: wavefunction cache for electron-phonon MPI communication |
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{{DISPLAYTITLE|ELPH_WF_CACHE_MB}} | |||
{{TAGDEF|ELPH_WF_CACHE_MB|real|1000}} | |||
Description: Maximum memory (in MB) allocated for caching wavefunctions during electron-phonon matrix element calculations. | |||
{{Available|6.5.1}} | |||
---- | |||
Electron-phonon matrix elements are sandwiches of the form | |||
⟨ψ<sub>n'''k'''</sub>|ΔV<sub>'''q'''</sub>|ψ<sub>m'''k'''′</sub>⟩, | |||
where '''k'''′ = '''k''' + '''q'''. Because k-points are distributed across MPI ranks, the wavefunction ψ<sub>n'''k'''</sub> needed to form the bra may reside on a different rank than the one computing the matrix element. <code>ELPH_WF_CACHE_MB</code> 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 <code>ELPH_WF_CACHE_MB</code>. | |||
{{NB|text=If the cache fills during the calculation, VASP aborts with the message <code>wf cache is full</code>. Increase <code>ELPH_WF_CACHE_MB</code> until the error no longer occurs.}} | |||
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. | |||
==Related tags and articles== | |||
{{TAG|ELPH_MELS}}, {{TAG|ELPH_NQBATCH}}, {{TAG|ELPH_NSIM}}, {{TAG|ELPH_RUN}} | |||
[[Category:INCAR tag]][[Category:Electron-phonon interactions]] | |||
Revision as of 12:14, 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.
| {{{2}}} |
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.