ELPH SELFEN BAND START KP: Difference between revisions
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{{DISPLAYTITLE:ELPH_SELFEN_BAND_START_KP}} | |||
{{TAGDEF|ELPH_SELFEN_BAND_START_KP|[integer]|-1}} | |||
Description: Index of the first k' band included in the electron self-energy sum; -1 uses all bands, and -2 activates automatic determination based on energy conservation. | |||
{{Available|6.5.1}} | |||
---- | |||
The Fan-Migdal self-energy involves a sum over intermediate scattering states at k' = k + q: | |||
:<math>\Sigma^{\text{FM}}_{n\mathbf{k}}(T) = \frac{1}{N_q}\sum_{m\nu\mathbf{q}} |g_{mn\mathbf{k},\nu\mathbf{q}}|^2 \left[\frac{\cdots}{\varepsilon_{n\mathbf{k}} - \varepsilon_{m\mathbf{k}+\mathbf{q}} \pm \omega_{\nu\mathbf{q}} + i\delta}\right]</math> | |||
{{TAG|ELPH_SELFEN_BAND_START_KP}} and {{TAG|ELPH_SELFEN_BAND_STOP_KP}} control the range of band indices m (at k') included in this sum. | |||
This is distinct from {{TAG|ELPH_SELFEN_BAND_START}} and {{TAG|ELPH_SELFEN_BAND_STOP}}, which select the bands n at k for which the self-energy is computed. | |||
The following values are accepted: | |||
* <code>-1</code> (default): include all bands from 1 to {{TAG|ELPH_NBANDS}}. | |||
* <code>-2</code>: determine the range automatically from energy conservation. Only k' bands whose eigenvalues fall within ±ω<sub>max</sub> of the target k bands are included, where ω<sub>max</sub> is the maximum phonon energy. This can significantly reduce the cost when {{TAG|ELPH_NBANDS}} is large. | |||
* Positive integer: use the specified band index as the lower bound. | |||
Setting both {{TAG|ELPH_SELFEN_BAND_START_KP}} and {{TAG|ELPH_SELFEN_BAND_STOP_KP}} to <code>-2</code> is recommended when a large number of bands is required for convergence but most of them lie far from the relevant energy window. | |||
==Related tags and articles== | |||
* {{TAG|ELPH_SELFEN_BAND_STOP_KP}} | |||
* {{TAG|ELPH_SELFEN_BAND_START}} | |||
* {{TAG|ELPH_NBANDS}} | |||
* {{TAG|ELPH_RUN}} | |||
[[Category:INCAR tag]][[Category:Electron-phonon_interactions]] | |||
Revision as of 11:59, 12 June 2026
ELPH_SELFEN_BAND_START_KP = [integer]
Default: ELPH_SELFEN_BAND_START_KP = -1
Description: Index of the first k' band included in the electron self-energy sum; -1 uses all bands, and -2 activates automatic determination based on energy conservation.
| Mind: Available as of VASP 6.5.1 |
The Fan-Migdal self-energy involves a sum over intermediate scattering states at k' = k + q:
- [math]\displaystyle{ \Sigma^{\text{FM}}_{n\mathbf{k}}(T) = \frac{1}{N_q}\sum_{m\nu\mathbf{q}} |g_{mn\mathbf{k},\nu\mathbf{q}}|^2 \left[\frac{\cdots}{\varepsilon_{n\mathbf{k}} - \varepsilon_{m\mathbf{k}+\mathbf{q}} \pm \omega_{\nu\mathbf{q}} + i\delta}\right] }[/math]
ELPH_SELFEN_BAND_START_KP and ELPH_SELFEN_BAND_STOP_KP control the range of band indices m (at k') included in this sum. This is distinct from ELPH_SELFEN_BAND_START and ELPH_SELFEN_BAND_STOP, which select the bands n at k for which the self-energy is computed.
The following values are accepted:
-1(default): include all bands from 1 to ELPH_NBANDS.-2: determine the range automatically from energy conservation. Only k' bands whose eigenvalues fall within ±ωmax of the target k bands are included, where ωmax is the maximum phonon energy. This can significantly reduce the cost when ELPH_NBANDS is large.- Positive integer: use the specified band index as the lower bound.
Setting both ELPH_SELFEN_BAND_START_KP and ELPH_SELFEN_BAND_STOP_KP to -2 is recommended when a large number of bands is required for convergence but most of them lie far from the relevant energy window.