ELPH WF CACHE MB: Difference between revisions

Revision as of 12:27, 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

[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.

@@ Line 7: / Line 7: @@
 Electron-phonon matrix elements are sandwiches of the form
-⟨ψ<sub>n'''k'''</sub>|ΔV<sub>'''q'''</sub>|ψ<sub>m'''k'''′</sub>⟩,
+:<math>\langle \psi_{n\mathbf{k}} | \Delta V_{\mathbf{q}} | \psi_{m\mathbf{k}'} \rangle,</math>
-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.
+where <math>\mathbf{k}' = \mathbf{k} + \mathbf{q}</math>. Because k-points are distributed across MPI ranks, the wavefunction <math>\psi_{n\mathbf{k}}</math> 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>.
-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 {{TAG|ELPH_WF_CACHE_PREFILL}} (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.
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