Electron-phonon potential from supercells - Revision history

Csheldon: /* Practical hints */

2026-02-09T11:02:13Z

Practical hints

← Older revision		Revision as of 11:02, 9 February 2026
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	== Practical hints ==		== Practical hints ==
	* You cannot know a priori how large a supercell to use; convergence tests must be performed. Even very large supercells can have noise, so it is important to start with a small cell and then work up to denser k- and q-points meshes, as well as larger supercells.		* You cannot know a priori how large a supercell to use; convergence tests must be performed. Even very large supercells can have noise, so it is important to start with a small cell and then work up to denser k- and q-points meshes, as well as larger supercells.
			* If you have imaginary frequencies during an electron-phonon calculation, the calculation will simply stop. This is an indication of improper convergence. You can work around this using {{TAG\|ELPH_IGNORE_IMAG_PHONONS}} to ignore the imaginary modes. This may be useful even for stable structures with small imaginary modes.

	== Related tags and articles ==		== Related tags and articles ==

Csheldon: /* Practical hints */

2026-02-09T10:16:55Z

Practical hints

← Older revision		Revision as of 10:16, 9 February 2026
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	== Practical hints ==		== Practical hints ==
	* You cannot know a priori how large a supercell to use. Even very large supercells can have noise, so it is important to start with a small cell and then work up to denser k- and q-points meshes, as well as larger supercells.		* You cannot know a priori how large a supercell to use; convergence tests must be performed. Even very large supercells can have noise, so it is important to start with a small cell and then work up to denser k- and q-points meshes, as well as larger supercells.

	== Related tags and articles ==		== Related tags and articles ==

Csheldon: /* Practical hints */

2026-02-09T10:16:09Z

Practical hints

← Older revision		Revision as of 10:16, 9 February 2026
Line 97:		Line 97:

	== Practical hints ==		== Practical hints ==
	* You cannot know a priori how large a supercell to use. Even very large supercells can have noise, so it is important to start with a small cell and then work up to ~~bigger cells and larger~~ k- and q-points meshes.		* You cannot know a priori how large a supercell to use. Even very large supercells can have noise, so it is important to start with a small cell and then work up to denser k- and q-points meshes, as well as larger supercells.

	== Related tags and articles ==		== Related tags and articles ==

Csheldon at 10:14, 9 February 2026

2026-02-09T10:14:51Z

← Older revision		Revision as of 10:14, 9 February 2026
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	The electron-phonon potential is Fourier interpolated from the FFT grid in the supercell to the supplied grid via a non-uniform FFT.		The electron-phonon potential is Fourier interpolated from the FFT grid in the supercell to the supplied grid via a non-uniform FFT.
	The results are written to the {{FILE\|phelel_params.hdf5}} file.		The results are written to the {{FILE\|phelel_params.hdf5}} file.

			== Practical hints ==
			* You cannot know a priori how large a supercell to use. Even very large supercells can have noise, so it is important to start with a small cell and then work up to bigger cells and larger k- and q-points meshes.

	== Related tags and articles ==		== Related tags and articles ==

Singraber at 08:04, 24 October 2025

2025-10-24T08:04:49Z

Csheldon at 08:39, 20 October 2025

2025-10-20T08:39:09Z

← Older revision		Revision as of 08:39, 20 October 2025
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	The supercell calculation and the primitive-cell calculation are performed in two separate VASP runs.		The supercell calculation and the primitive-cell calculation are performed in two separate VASP runs.
	This page provides an overview of the supercell calculation and how the electron-phonon potential can be calculated.		This page provides an overview of the supercell calculation and how the electron-phonon potential can be calculated.
	For information regarding the electron-phonon calculation in the primitive cell, consult the documentation on [[Bandgap renormalization due to electron-phonon coupling\|phonon-induced bandstructure renormalization]] and on [[Transport coefficients including electron-phonon scattering\|phonon-limited transport~~]]. For the theory on the electron-phonon potential, see the end of the self-energy section of the [[Electron-phonon interactions theory#Electron_self-energy\|theory page~~]].		For information regarding the electron-phonon calculation in the primitive cell, consult the documentation on [[Bandgap renormalization due to electron-phonon coupling\|phonon-induced bandstructure renormalization]] and on [[Transport coefficients including electron-phonon scattering\|phonon-limited transport]].

			For the theory on the electron-phonon potential, 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 08:37, 20 October 2025

2025-10-20T08:37:54Z

← Older revision		Revision as of 08:37, 20 October 2025
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	The supercell calculation and the primitive-cell calculation are performed in two separate VASP runs.		The supercell calculation and the primitive-cell calculation are performed in two separate VASP runs.
	This page provides an overview of the supercell calculation and how the electron-phonon potential can be calculated.		This page provides an overview of the supercell calculation and how the electron-phonon potential can be calculated.
	For information regarding the ~~theory~~ electron-phonon calculation in the primitive cell, consult the documentation on [[Bandgap renormalization due to electron-phonon coupling\|phonon-induced bandstructure renormalization]] and on [[Transport coefficients including electron-phonon scattering\|phonon-limited transport]].		For information regarding the electron-phonon calculation in the primitive cell, consult the documentation on [[Bandgap renormalization due to electron-phonon coupling\|phonon-induced bandstructure renormalization]] and on [[Transport coefficients including electron-phonon scattering\|phonon-limited transport]]. For the theory on the electron-phonon potential, 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}}

Csheldon at 08:37, 20 October 2025

2025-10-20T08:37:18Z

← Older revision		Revision as of 08:37, 20 October 2025
Line 13:		Line 13:
	The supercell calculation and the primitive-cell calculation are performed in two separate VASP runs.		The supercell calculation and the primitive-cell calculation are performed in two separate VASP runs.
	This page provides an overview of the supercell calculation and how the electron-phonon potential can be calculated.		This page provides an overview of the supercell calculation and how the electron-phonon potential can be calculated.
	For information regarding the electron-phonon calculation in the primitive cell, consult the documentation on [[Bandgap renormalization due to electron-phonon coupling\|phonon-induced bandstructure renormalization]] and on [[Transport coefficients including electron-phonon scattering\|phonon-limited transport]].		For information regarding the theory electron-phonon calculation in the primitive cell, consult the documentation on [[Bandgap renormalization due to electron-phonon coupling\|phonon-induced bandstructure renormalization]] and on [[Transport coefficients including electron-phonon scattering\|phonon-limited transport]].

	{{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

2025-10-16T14:08:56Z

← Older revision		Revision as of 14:08, 16 October 2025
Line 13:		Line 13:
	The supercell calculation and the primitive-cell calculation are performed in two separate VASP runs.		The supercell calculation and the primitive-cell calculation are performed in two separate VASP runs.
	This page provides an overview of the supercell calculation and how the electron-phonon potential can be calculated.		This page provides an overview of the supercell calculation and how the electron-phonon potential can be calculated.
	For information regarding the electron-phonon calculation in the primitive cell, consult the documentation on [[Bandgap renormalization due to electron-phonon coupling\|phonon-induced bandstructure renormalization]] and on [[Transport coefficients including electron-phonon scattering\|phonon-~~mediated~~ transport]].		For information regarding the electron-phonon calculation in the primitive cell, consult the documentation on [[Bandgap renormalization due to electron-phonon coupling\|phonon-induced bandstructure renormalization]] and on [[Transport coefficients including electron-phonon scattering\|phonon-limited transport]].
	{{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: Add HDF5 disclaimer

2025-10-16T14:08:22Z

Add HDF5 disclaimer

← Older revision		Revision as of 14:08, 16 October 2025
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	For information regarding the electron-phonon calculation in the primitive cell, consult the documentation on [[Bandgap renormalization due to electron-phonon coupling\|phonon-induced bandstructure renormalization]] and on [[Transport coefficients including electron-phonon scattering\|phonon-mediated transport]].		For information regarding the electron-phonon calculation in the primitive cell, consult the documentation on [[Bandgap renormalization due to electron-phonon coupling\|phonon-induced bandstructure renormalization]] and on [[Transport coefficients including electron-phonon scattering\|phonon-mediated transport]].
	{{Available\|6.5.0}}		{{Available\|6.5.0}}
			{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}
	{{NB\|tip\|The entire workflow of initializing a calculation, computing the electron-phonon potential in the supercell and performing subsequent electron-phonon calculations in the primitive cell can be facilitated by <tt>velph</tt>. <tt>velph</tt> is a command-line tool included in the [https://github.com/phonopy/phelel phelel] python package. It helps guide you through the process step by step and ensures a certain level of consistency between the required VASP calculations.}}		{{NB\|tip\|The entire workflow of initializing a calculation, computing the electron-phonon potential in the supercell and performing subsequent electron-phonon calculations in the primitive cell can be facilitated by <tt>velph</tt>. <tt>velph</tt> is a command-line tool included in the [https://github.com/phonopy/phelel phelel] python package. It helps guide you through the process step by step and ensures a certain level of consistency between the required VASP calculations.}}

← Older revision		Revision as of 14:08, 16 October 2025
Line 15:		Line 15:
	For information regarding the electron-phonon calculation in the primitive cell, consult the documentation on [[Bandgap renormalization due to electron-phonon coupling\|phonon-induced bandstructure renormalization]] and on [[Transport coefficients including electron-phonon scattering\|phonon-mediated transport]].		For information regarding the electron-phonon calculation in the primitive cell, consult the documentation on [[Bandgap renormalization due to electron-phonon coupling\|phonon-induced bandstructure renormalization]] and on [[Transport coefficients including electron-phonon scattering\|phonon-mediated transport]].
	{{Available\|6.5.0}}		{{Available\|6.5.0}}
			{{NB\|important\|This feature requires [[:Category:HDF5_support \| HDF5 support]].}}
	{{NB\|tip\|The entire workflow of initializing a calculation, computing the electron-phonon potential in the supercell and performing subsequent electron-phonon calculations in the primitive cell can be facilitated by <tt>velph</tt>. <tt>velph</tt> is a command-line tool included in the [https://github.com/phonopy/phelel phelel] python package. It helps guide you through the process step by step and ensures a certain level of consistency between the required VASP calculations.}}		{{NB\|tip\|The entire workflow of initializing a calculation, computing the electron-phonon potential in the supercell and performing subsequent electron-phonon calculations in the primitive cell can be facilitated by <tt>velph</tt>. <tt>velph</tt> is a command-line tool included in the [https://github.com/phonopy/phelel phelel] python package. It helps guide you through the process step by step and ensures a certain level of consistency between the required VASP calculations.}}

← Older revision		Revision as of 08:04, 24 October 2025
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	=== VASP internal driver ===		=== VASP internal driver ===

	This way of calculating the electron-phonon potential is activated by setting {{~~TAGO~~\|ELPH_POT_GENERATE\|True}} in the {{FILE\|INCAR}} file.		This way of calculating the electron-phonon potential is activated by setting {{TAG\|ELPH_POT_GENERATE\|True}} in the {{FILE\|INCAR}} file.
	It utilizes the VASP-internal finite-difference driver that is activated by setting {{~~TAGO~~\|IBRION\|6}} in the {{FILE\|INCAR}} file.		It utilizes the VASP-internal finite-difference driver that is activated by setting {{TAG\|IBRION\|6}} in the {{FILE\|INCAR}} file.
	The atomic displacement directions are automatically determined by VASP.		The atomic displacement directions are automatically determined by VASP.
	As usual, {{TAG\|POTIM}} and {{TAG\|NFREE}} can be used to control the displacement amount and finite-difference stencil, respectively.		As usual, {{TAG\|POTIM}} and {{TAG\|NFREE}} can be used to control the displacement amount and finite-difference stencil, respectively.
	This is the same procedure used to calculate [[phonons from finite differences]] and many of the same considerations regarding performance and accuracy apply in this case.		This is the same procedure used to calculate [[phonons from finite differences]] and many of the same considerations regarding performance and accuracy apply in this case.
	Therefore, phonon frequencies are a great way to test the convergence with respect to supercell size.		Therefore, phonon frequencies are a great way to test the convergence with respect to supercell size.
	{{NB\|mind\|Currently, VASP generates more displacements with {{~~TAGO~~\|ELPH_POT_GENERATE\|True}} and {{~~TAGO~~\|IBRION\|6}} than would be required in principle. This will be improved in a future version of the code.}}		{{NB\|mind\|Currently, VASP generates more displacements with {{TAG\|ELPH_POT_GENERATE\|True}} and {{TAG\|IBRION\|6}} than would be required in principle. This will be improved in a future version of the code.}}

	Once the electron-phonon potential is obtained, it is automatically mapped to the primitive cell.		Once the electron-phonon potential is obtained, it is automatically mapped to the primitive cell.
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	In addition, the file <tt>SPOSCAR</tt> is created which contains the supercell geometry in equilibrium.		In addition, the file <tt>SPOSCAR</tt> is created which contains the supercell geometry in equilibrium.

	For each of the generated POSCAR files, create a separate directory and run VASP there with {{~~TAGO~~\|ELPH_PREPARE\|True}} set in the {{FILE\|INCAR}} file.		For each of the generated POSCAR files, create a separate directory and run VASP there with {{TAG\|ELPH_PREPARE\|True}} set in the {{FILE\|INCAR}} file.
	This setting instructs VASP to write the potential as well as other important information to disk.		This setting instructs VASP to write the potential as well as other important information to disk.
	Finally, run phelel to combine all the data from the individual directories to obtain the electron-phonon potential, for example,		Finally, run phelel to combine all the data from the individual directories to obtain the electron-phonon potential, for example,