Bandgap renormalization due to electron-phonon coupling - Revision history

Csheldon at 11:09, 22 January 2026

2026-01-22T11:09:38Z

← Older revision		Revision as of 11:09, 22 January 2026
Line 7:		Line 7:
	{{Available\|6.5.0}}		{{Available\|6.5.0}}
	{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}		{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}
	{{NB\|warning\|There is a [[Known_issues#KnownIssue54 \| known issue]] ~~with~~ {{TAG\|ISPIN\|2}} for VASP 6.5.0 and 6.5.1 ~~(see [https://vasp.at/forum/viewtopic.php?t=20541#p33020 this forum post]). It~~ was fixed in VASP 6.6.0 ~~onwards~~.}}		{{NB\|warning\|There was a [[Known_issues#KnownIssue54 \| known issue]] for electron-phonon calculations using {{TAG\|ISPIN\|2}} for VASP 6.5.0 and 6.5.1 that was fixed in VASP 6.6.0.}}
	{{NB\|tip\|The phonon-induced renormalization of the fundamental gap can alternatively be calculated from a [[Electron-phonon_interactions_from_Monte-Carlo_sampling \| stochastic approach]].}}		{{NB\|tip\|The phonon-induced renormalization of the fundamental gap can alternatively be calculated from a [[Electron-phonon_interactions_from_Monte-Carlo_sampling \| stochastic approach]].}}

Csheldon at 11:07, 22 January 2026

2026-01-22T11:07:01Z

← Older revision		Revision as of 11:07, 22 January 2026
Line 7:		Line 7:
	{{Available\|6.5.0}}		{{Available\|6.5.0}}
	{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}		{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}
			{{NB\|warning\|There is a [[Known_issues#KnownIssue54 \| known issue]] with {{TAG\|ISPIN\|2}} for VASP 6.5.0 and 6.5.1 (see [https://vasp.at/forum/viewtopic.php?t=20541#p33020 this forum post]). It was fixed in VASP 6.6.0 onwards.}}
	{{NB\|tip\|The phonon-induced renormalization of the fundamental gap can alternatively be calculated from a [[Electron-phonon_interactions_from_Monte-Carlo_sampling \| stochastic approach]].}}		{{NB\|tip\|The phonon-induced renormalization of the fundamental gap can alternatively be calculated from a [[Electron-phonon_interactions_from_Monte-Carlo_sampling \| stochastic approach]].}}

Singraber at 08:05, 24 October 2025

2025-10-24T08:05:20Z

Mani: /* Basic usage */ Add ELPH_MODE mention

2025-10-21T13:40:06Z

Basic usage: Add ELPH_MODE mention

← Older revision		Revision as of 13:40, 21 October 2025
Line 39:		Line 39:
	{{TAGBL\|ELPH_SELFEN_DW}} = .TRUE.		{{TAGBL\|ELPH_SELFEN_DW}} = .TRUE.
	{{TAGBL\|ELPH_SELFEN_GAPS}} = .TRUE.		{{TAGBL\|ELPH_SELFEN_GAPS}} = .TRUE.

			{{NB\|tip\|For your convenience, you can set {{TAGO\|ELPH_MODE\|renorm}}, which automatically sets reasonable values for many of these electron-phonon tags to perform the band-gap renormalization. It is still possible to manually overwrite the chosen values.}}

	To get an accurate value while using the smallest possible amount of computational resources, we recommend performing a basis set and k-point sampling convergence study.		To get an accurate value while using the smallest possible amount of computational resources, we recommend performing a basis set and k-point sampling convergence study.

Csheldon at 08:38, 20 October 2025

2025-10-20T08:38:31Z

← Older revision		Revision as of 08:38, 20 October 2025
Line 4:		Line 4:
	The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.		The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.

	For the theory on bandgap renormalization from perturbation theory, see ~~the end of~~ the many-body perturbation theory section of the [[Electron-phonon interactions theory#Electron_self-energy\|theory page]].		For the theory on bandgap renormalization from perturbation theory, see the many-body perturbation theory section of the [[Electron-phonon interactions theory#Electron_self-energy\|theory page]].
	{{Available\|6.5.0}}		{{Available\|6.5.0}}
	{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}		{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}

Csheldon at 08:38, 20 October 2025

2025-10-20T08:38:15Z

← Older revision		Revision as of 08:38, 20 October 2025
Line 4:		Line 4:
	The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.		The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.

	For the theory on bandgap renormalization from perturbation theory, see the end of the ~~self~~-~~energy~~ section of the [[Electron-phonon interactions theory#Electron_self-energy\|theory page]].		For the theory on bandgap renormalization from perturbation theory, see the end of the many-body perturbation theory section of the [[Electron-phonon interactions theory#Electron_self-energy\|theory page]].
	{{Available\|6.5.0}}		{{Available\|6.5.0}}
	{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}		{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}

Csheldon at 08:35, 20 October 2025

2025-10-20T08:35:55Z

← Older revision		Revision as of 08:35, 20 October 2025
Line 4:		Line 4:
	The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.		The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.

	For the theory on bandgap renormalization from perturbation theory, see the [[Electron-phonon interactions theory#~~Electron~~-~~phonon interactions from perturbation theory~~\|theory page]].		For the theory on bandgap renormalization from perturbation theory, see the end of the self-energy section of the [[Electron-phonon interactions theory#Electron_self-energy\|theory page]].
	{{Available\|6.5.0}}		{{Available\|6.5.0}}
	{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}		{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}

Csheldon at 08:32, 20 October 2025

2025-10-20T08:32:39Z

← Older revision		Revision as of 08:32, 20 October 2025
Line 3:		Line 3:
	For the particular case where we want to determine the bandgap, we can compute the self-energy only for the states that form the gap (including all the degenerate states).		For the particular case where we want to determine the bandgap, we can compute the self-energy only for the states that form the gap (including all the degenerate states).
	The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.		The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.

			For the theory on bandgap renormalization from perturbation theory, see the [[Electron-phonon interactions theory#Electron-phonon interactions from perturbation theory\|theory page]].
	{{Available\|6.5.0}}		{{Available\|6.5.0}}
	{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}		{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}

Mani at 14:08, 16 October 2025

2025-10-16T14:08:04Z

← Older revision		Revision as of 14:08, 16 October 2025
Line 4:		Line 4:
	The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.		The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.
	{{Available\|6.5.0}}		{{Available\|6.5.0}}
	{{NB\|important\|This ~~features~~ requires [[:Category:HDF5_support \| HDF5 support]].}}		{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}
	{{NB\|tip\|The phonon-induced renormalization of the fundamental gap can alternatively be calculated from a [[Electron-phonon_interactions_from_Monte-Carlo_sampling \| stochastic approach]].}}		{{NB\|tip\|The phonon-induced renormalization of the fundamental gap can alternatively be calculated from a [[Electron-phonon_interactions_from_Monte-Carlo_sampling \| stochastic approach]].}}

Mani: Add HDF5 disclaimer

2025-10-16T14:07:46Z

Add HDF5 disclaimer

← Older revision		Revision as of 14:07, 16 October 2025
Line 4:		Line 4:
	The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.		The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.
	{{Available\|6.5.0}}		{{Available\|6.5.0}}
			{{NB\|important\|This features requires [[:Category:HDF5_support \| HDF5 support]].}}
	{{NB\|tip\|The phonon-induced renormalization of the fundamental gap can alternatively be calculated from a [[Electron-phonon_interactions_from_Monte-Carlo_sampling \| stochastic approach]].}}		{{NB\|tip\|The phonon-induced renormalization of the fundamental gap can alternatively be calculated from a [[Electron-phonon_interactions_from_Monte-Carlo_sampling \| stochastic approach]].}}

← Older revision		Revision as of 11:09, 22 January 2026
Line 7:		Line 7:
	{{Available\|6.5.0}}		{{Available\|6.5.0}}
	{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}		{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}
	{{NB\|warning\|There is a [[Known_issues#KnownIssue54 \| known issue]] ~~with~~ {{TAG\|ISPIN\|2}} for VASP 6.5.0 and 6.5.1 ~~(see [https://vasp.at/forum/viewtopic.php?t=20541#p33020 this forum post]). It~~ was fixed in VASP 6.6.0 ~~onwards~~.}}		{{NB\|warning\|There was a [[Known_issues#KnownIssue54 \| known issue]] for electron-phonon calculations using {{TAG\|ISPIN\|2}} for VASP 6.5.0 and 6.5.1 that was fixed in VASP 6.6.0.}}
	{{NB\|tip\|The phonon-induced renormalization of the fundamental gap can alternatively be calculated from a [[Electron-phonon_interactions_from_Monte-Carlo_sampling \| stochastic approach]].}}		{{NB\|tip\|The phonon-induced renormalization of the fundamental gap can alternatively be calculated from a [[Electron-phonon_interactions_from_Monte-Carlo_sampling \| stochastic approach]].}}

← Older revision		Revision as of 11:07, 22 January 2026
Line 7:		Line 7:
	{{Available\|6.5.0}}		{{Available\|6.5.0}}
	{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}		{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}
			{{NB\|warning\|There is a [[Known_issues#KnownIssue54 \| known issue]] with {{TAG\|ISPIN\|2}} for VASP 6.5.0 and 6.5.1 (see [https://vasp.at/forum/viewtopic.php?t=20541#p33020 this forum post]). It was fixed in VASP 6.6.0 onwards.}}
	{{NB\|tip\|The phonon-induced renormalization of the fundamental gap can alternatively be calculated from a [[Electron-phonon_interactions_from_Monte-Carlo_sampling \| stochastic approach]].}}		{{NB\|tip\|The phonon-induced renormalization of the fundamental gap can alternatively be calculated from a [[Electron-phonon_interactions_from_Monte-Carlo_sampling \| stochastic approach]].}}

← Older revision		Revision as of 08:38, 20 October 2025
Line 4:		Line 4:
	The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.		The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.

	For the theory on bandgap renormalization from perturbation theory, see ~~the end of~~ the many-body perturbation theory section of the [[Electron-phonon interactions theory#Electron_self-energy\|theory page]].		For the theory on bandgap renormalization from perturbation theory, see the many-body perturbation theory section of the [[Electron-phonon interactions theory#Electron_self-energy\|theory page]].
	{{Available\|6.5.0}}		{{Available\|6.5.0}}
	{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}		{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}

← Older revision		Revision as of 08:38, 20 October 2025
Line 4:		Line 4:
	The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.		The selection of these states can be done automatically by VASP using {{TAGO\|ELPH_SELFEN_GAPS\|True}}.

	For the theory on bandgap renormalization from perturbation theory, see the end of the ~~self~~-~~energy~~ section of the [[Electron-phonon interactions theory#Electron_self-energy\|theory page]].		For the theory on bandgap renormalization from perturbation theory, see the end of the many-body perturbation theory section of the [[Electron-phonon interactions theory#Electron_self-energy\|theory page]].
	{{Available\|6.5.0}}		{{Available\|6.5.0}}
	{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}		{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}

← Older revision		Revision as of 08:05, 24 October 2025
Line 1:		Line 1:
	The band-structure renormalization within the nonadiabatic Allen Heine Cardona (AHC) theory is computed from the real part of the electron self-energy evaluated at the Kohn-Sham (KS) eigenvalue.		The band-structure renormalization within the nonadiabatic Allen Heine Cardona (AHC) theory is computed from the real part of the electron self-energy evaluated at the Kohn-Sham (KS) eigenvalue.
	This calculation is activated by default when {{~~TAGO~~\|ELPH_RUN\|True}} and {{~~TAGO~~\|ELPH_DRIVER\|EL}}.		This calculation is activated by default when {{TAG\|ELPH_RUN\|True}} and {{TAG\|ELPH_DRIVER\|EL}}.
	For the particular case where we want to determine the bandgap, we can compute the self-energy only for the states that form the gap (including all the degenerate states).		For the particular case where we want to determine the bandgap, we can compute the self-energy only for the states that form the gap (including all the degenerate states).
	The selection of these states can be done automatically by VASP using {{~~TAGO~~\|ELPH_SELFEN_GAPS\|True}}.		The selection of these states can be done automatically by VASP using {{TAG\|ELPH_SELFEN_GAPS\|True}}.

	For the theory on bandgap renormalization from perturbation theory, see the many-body perturbation theory section of the [[Electron-phonon interactions theory#Electron_self-energy\|theory page]].		For the theory on bandgap renormalization from perturbation theory, see the many-body perturbation theory section of the [[Electron-phonon interactions theory#Electron_self-energy\|theory page]].
Line 40:		Line 40:
	{{TAGBL\|ELPH_SELFEN_GAPS}} = .TRUE.		{{TAGBL\|ELPH_SELFEN_GAPS}} = .TRUE.

	{{NB\|tip\|For your convenience, you can set {{~~TAGO~~\|ELPH_MODE\|renorm}}, which automatically sets reasonable values for many of these electron-phonon tags to perform the band-gap renormalization. It is still possible to manually overwrite the chosen values.}}		{{NB\|tip\|For your convenience, you can set {{TAG\|ELPH_MODE\|renorm}}, which automatically sets reasonable values for many of these electron-phonon tags to perform the band-gap renormalization. It is still possible to manually overwrite the chosen values.}}

	To get an accurate value while using the smallest possible amount of computational resources, we recommend performing a basis set and k-point sampling convergence study.		To get an accurate value while using the smallest possible amount of computational resources, we recommend performing a basis set and k-point sampling convergence study.
Line 48:		Line 48:

	==Basis set convergence==		==Basis set convergence==
	First, we will deal with convergence of the bandgap renormalization with respect to the number of electronic states ({{TAG\|NBANDS}}) and plane-waves ({{TAG\|ENCUT}}). To avoid a more cumbersome double-convergence with {{TAG\|ENCUT}} and {{TAG\|ELPH_NBANDS}} we recommend setting {{TAG\|ELPH_NBANDS}} to be equal to the maximum number of plane-waves. This can be done automatically by setting {{~~TAGO~~\|ELPH_NBANDS\|-2}}.		First, we will deal with convergence of the bandgap renormalization with respect to the number of electronic states ({{TAG\|NBANDS}}) and plane-waves ({{TAG\|ENCUT}}). To avoid a more cumbersome double-convergence with {{TAG\|ENCUT}} and {{TAG\|ELPH_NBANDS}} we recommend setting {{TAG\|ELPH_NBANDS}} to be equal to the maximum number of plane-waves. This can be done automatically by setting {{TAG\|ELPH_NBANDS\|-2}}.

	The derivatives of the electron-phonon potential are contained in the {{FILE\|phelel_params.hdf5}} file on a pre-selected grid ({{TAG\|NGX}}, {{TAG\|NGY}}, {{TAG\|NGZ}}).		The derivatives of the electron-phonon potential are contained in the {{FILE\|phelel_params.hdf5}} file on a pre-selected grid ({{TAG\|NGX}}, {{TAG\|NGY}}, {{TAG\|NGZ}}).
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	This allows running the calculation with different values of {{TAG\|ENCUT}} and monitoring how that affects the final value of the bandgap renormalization.		This allows running the calculation with different values of {{TAG\|ENCUT}} and monitoring how that affects the final value of the bandgap renormalization.

	Let us consider an example calculation where the electron-phonon potential was generated for Silicon with an {{~~TAGO~~\|ENCUT\|500}} which yields {{TAG\|NGX}}={{TAG\|NGY}}={{TAG\|NGZ}}=28 in the primitive cell. The values of {{TAG\|NGX}}, {{TAG\|NGY}} and {{TAG\|NGZ}} chosen by VASP can be monitored in the {{FILE\|OUTCAR}} file.		Let us consider an example calculation where the electron-phonon potential was generated for Silicon with an {{TAG\|ENCUT\|500}} which yields {{TAG\|NGX}}={{TAG\|NGY}}={{TAG\|NGZ}}=28 in the primitive cell. The values of {{TAG\|NGX}}, {{TAG\|NGY}} and {{TAG\|NGZ}} chosen by VASP can be monitored in the {{FILE\|OUTCAR}} file.
	A convergence study can be performed by running multiple calculations with {{TAG\|ENCUT}}=200, then 300, then 400 and finally 500.		A convergence study can be performed by running multiple calculations with {{TAG\|ENCUT}}=200, then 300, then 400 and finally 500.
	{{~~TAGO~~\|NGX\|28}}, {{~~TAGO~~\|NGY\|28}} and {{~~TAGO~~\|NGZ\|28}} are set explicitly in the {{FILE\|INCAR}} file.		{{TAG\|NGX\|28}}, {{TAG\|NGY\|28}} and {{TAG\|NGZ\|28}} are set explicitly in the {{FILE\|INCAR}} file.
	You can verify that the calculations with a lower cutoff run faster, highlighting the importance of convergence tests for reaching a good compromise between accuracy and computational time.		You can verify that the calculations with a lower cutoff run faster, highlighting the importance of convergence tests for reaching a good compromise between accuracy and computational time.