ELPH USERECIP: Difference between revisions
Add ELPH_USERECIP tag page: reciprocal-space matrix elements, auto-enabled for meta-GGAs |
m Huebsch moved page Construction:ELPH USERECIP to ELPH USERECIP without leaving a redirect |
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{{DISPLAYTITLE | {{DISPLAYTITLE:ELPH_USERECIP}} | ||
{{TAGDEF|ELPH_USERECIP|logical|.FALSE.}} | {{TAGDEF|ELPH_USERECIP|logical|.FALSE.}} | ||
Description: Computes electron-phonon matrix elements in reciprocal space instead of real space. | Description: Computes electron-phonon matrix elements in reciprocal space instead of real space. | ||
{{Available|6.5.0}} | {{Available|6.5.0}} | ||
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The electron-phonon matrix element | The electron-phonon matrix element | ||
:<math>\langle \psi_{n\mathbf{k}} | \Delta V_{\mathbf{q}} | \psi_{m\mathbf{k}'} \rangle</math> | :<math>\langle \psi_{n\mathbf{k}} | \Delta V_{\mathbf{q}} | \psi_{m\mathbf{k}'} \rangle</math> | ||
can be evaluated either in real space (the default) or in reciprocal space as a contraction over plane-wave coefficients. | can be evaluated either in real space (the default) or in reciprocal space as a contraction over plane-wave coefficients. {{TAG|ELPH_USERECIP|.TRUE.}} selects the reciprocal-space path. | ||
'''Automatic activation for meta-GGAs.''' When a meta-GGA functional is used, VASP sets | '''Automatic activation for meta-GGAs.''' When a meta-GGA functional is used, VASP sets {{TAG|ELPH_USERECIP|.TRUE.}} automatically. This is required because the kinetic-energy density contribution to the electron-phonon potential is non-local in real space and can only be evaluated in reciprocal space. | ||
'''Band structure renormalization.''' The reciprocal-space path can also be beneficial for calculations where the number of bra k-points (<math>n_\mathbf{k}</math>) is much smaller than the number of ket k-points (<math>n_{\mathbf{k}'}</math>), such as band structure renormalization along high-symmetry lines. In this case the real-space path would require an FFT for each bra state, whereas the reciprocal-space path works directly with the stored plane-wave coefficients and avoids these transforms. | '''Band structure renormalization.''' The reciprocal-space path can also be beneficial for calculations where the number of bra k-points (<math>n_\mathbf{k}</math>) is much smaller than the number of ket k-points (<math>n_{\mathbf{k}'}</math>), such as band structure renormalization along high-symmetry lines. In this case the real-space path would require an FFT for each bra state, whereas the reciprocal-space path works directly with the stored plane-wave coefficients and avoids these transforms. | ||
==Related tags and articles== | ==Related tags and articles== | ||
* {{TAG|ELPH_USEBLAS}} | * {{TAG|ELPH_USEBLAS}} | ||
* {{TAG|ELPH_RUN}} | * {{TAG|ELPH_RUN}} | ||
[[Category:INCAR tag]][[Category:Electron-phonon interactions]] | [[Category:INCAR tag]][[Category:Electron-phonon interactions]] | ||
Latest revision as of 13:56, 18 June 2026
ELPH_USERECIP = logical
Default: ELPH_USERECIP = .FALSE.
Description: Computes electron-phonon matrix elements in reciprocal space instead of real space.
| Mind: Available as of VASP 6.5.0 |
The electron-phonon matrix element
- [math]\displaystyle{ \langle \psi_{n\mathbf{k}} | \Delta V_{\mathbf{q}} | \psi_{m\mathbf{k}'} \rangle }[/math]
can be evaluated either in real space (the default) or in reciprocal space as a contraction over plane-wave coefficients. ELPH_USERECIP = .TRUE. selects the reciprocal-space path.
Automatic activation for meta-GGAs. When a meta-GGA functional is used, VASP sets ELPH_USERECIP = .TRUE. automatically. This is required because the kinetic-energy density contribution to the electron-phonon potential is non-local in real space and can only be evaluated in reciprocal space.
Band structure renormalization. The reciprocal-space path can also be beneficial for calculations where the number of bra k-points ([math]\displaystyle{ n_\mathbf{k} }[/math]) is much smaller than the number of ket k-points ([math]\displaystyle{ n_{\mathbf{k}'} }[/math]), such as band structure renormalization along high-symmetry lines. In this case the real-space path would require an FFT for each bra state, whereas the reciprocal-space path works directly with the stored plane-wave coefficients and avoids these transforms.