Computing the phonon dispersion and DOS - Revision history

Csheldon: /* Practical hints */

2026-02-09T10:05:38Z

Practical hints

← Older revision		Revision as of 10:05, 9 February 2026
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	== Practical hints ==		== Practical hints ==
	*Bear in mind that the choice of exchange-correlation functional can have a big impact on the [[Born effective charges]] and the [[:Category:Dielectric_properties#Dielectric_function \| dielectric function]], and thereby the LO-TO splitting.		*Bear in mind that the choice of exchange-correlation functional (e.g., GGA or hybrid functionals) can have a big impact on the [[Born effective charges]] and the [[:Category:Dielectric_properties#Dielectric_function \| dielectric function]], and thereby the LO-TO splitting and phonon dispersion.

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

Csheldon at 09:59, 9 February 2026

2026-02-09T09:59:54Z

← Older revision		Revision as of 09:59, 9 February 2026
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	This results in discontinuities around the Γ-point when <math>\mathbf{q} \to \mathbf{0}</math>, as shown in the accompanying figure.		This results in discontinuities around the Γ-point when <math>\mathbf{q} \to \mathbf{0}</math>, as shown in the accompanying figure.

	==== Practical hints ====		== Practical hints ==
	*Bear in mind that the choice of exchange-correlation functional can have a big impact on the [[Born effective charges]] and the [[:Category:Dielectric_properties#Dielectric_function \| dielectric function]], and thereby the LO-TO splitting.		*Bear in mind that the choice of exchange-correlation functional can have a big impact on the [[Born effective charges]] and the [[:Category:Dielectric_properties#Dielectric_function \| dielectric function]], and thereby the LO-TO splitting.

Csheldon: /* LO-TO splitting */

2026-02-09T09:59:43Z

LO-TO splitting

← Older revision		Revision as of 09:59, 9 February 2026
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	This results in discontinuities around the Γ-point when <math>\mathbf{q} \to \mathbf{0}</math>, as shown in the accompanying figure.		This results in discontinuities around the Γ-point when <math>\mathbf{q} \to \mathbf{0}</math>, as shown in the accompanying figure.

	~~{{NB\|mind\|~~Bear in mind that the choice of exchange-correlation functional can have a big impact on the [[Born effective charges]] and the [[:Category:Dielectric_properties#Dielectric_function \| dielectric function]], and thereby the LO-TO splitting.}}		==== Practical hints ====
			*Bear in mind that the choice of exchange-correlation functional can have a big impact on the [[Born effective charges]] and the [[:Category:Dielectric_properties#Dielectric_function \| dielectric function]], and thereby the LO-TO splitting.

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

Csheldon: /* LO-TO splitting */

2026-02-09T09:56:02Z

LO-TO splitting

← Older revision		Revision as of 09:56, 9 February 2026
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	The phonon frequencies obtained by including the long-range dipole corrections are therefore more dependent on the direction of the phonon wave vector, <math>\mathbf{q}</math>.		The phonon frequencies obtained by including the long-range dipole corrections are therefore more dependent on the direction of the phonon wave vector, <math>\mathbf{q}</math>.
	This results in discontinuities around the Γ-point when <math>\mathbf{q} \to \mathbf{0}</math>, as shown in the accompanying figure.		This results in discontinuities around the Γ-point when <math>\mathbf{q} \to \mathbf{0}</math>, as shown in the accompanying figure.

			{{NB\|mind\|Bear in mind that the choice of exchange-correlation functional can have a big impact on the [[Born effective charges]] and the [[:Category:Dielectric_properties#Dielectric_function \| dielectric function]], and thereby the LO-TO splitting.}}

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

Singraber at 08:01, 24 October 2025

2025-10-24T08:01:15Z

Huebsch at 07:40, 20 October 2025

2025-10-20T07:40:14Z

← Older revision		Revision as of 07:40, 20 October 2025
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	{{TAG \| PHON_BORN_CHARGES}},		{{TAG \| PHON_BORN_CHARGES}},
	{{TAG \| PHON_G_CUTOFF}}		{{TAG \| PHON_G_CUTOFF}}

			== References ==

	[[Category:Phonons]][[Category:Howto]]		[[Category:Phonons]][[Category:Howto]]

Miranda.henrique: /* Step 2: Provide q-points along a high-symmetry path */

2025-10-15T11:54:23Z

Step 2: Provide q-points along a high-symmetry path

← Older revision		Revision as of 11:54, 15 October 2025
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	Create a {{FILE\|QPOINTS}} file containing a '''q'''-points path at which the phonon dispersion is computed.		Create a {{FILE\|QPOINTS}} file containing a '''q'''-points path at which the phonon dispersion is computed.
	This is accomplished using the [[KPOINTS#Band-structure calculations\|line mode]] of the {{FILE\|KPOINTS}}-file format.		This is accomplished using the [[KPOINTS#Band-structure calculations\|line mode]] of the {{FILE\|KPOINTS}}-file format.
			External tools{{cite\|bilbao:kvec}}{{cite\|seekpath}} are useful to decide which paths in the Brillouin zone to include. The tools provide the coordinates and the labels for a given structure.

	=== Step 3: Compute the phonon dispersion ===		=== Step 3: Compute the phonon dispersion ===

Mani: /* Polar materials */ Expand section, give more details for how to set dielectric properties and show examples of LO-TO splitting

2024-02-23T15:31:39Z

Polar materials: Expand section, give more details for how to set dielectric properties and show examples of LO-TO splitting

@@ Line 51: / Line 51: @@
 == Polar materials ==
 If the material is polar, i.e., two or more atoms in the unit cell carry non-zero Born effective charge tensors, the long-range dipole-dipole interaction has to be treated by [[Phonons:_Theory#Long-range_interatomic_force_constants_.28LO-TO_splitting.29|Ewald summation]].
 This is achieved by setting {{TAGO|LPHON_POLAR|True}}, supplying the static dielectric tensor ({{TAG|PHON_DIELECTRIC}}) and the Born-effective charges ({{TAG|PHON_BORN_CHARGES}}).
-The values for these have to be obtained from a separate VASP calculation in the unit cell setting {{TAG|LEPSILON}} or {{TAG|LCALCEPS}}.
+The values for these dielectric properties have to be obtained from a separate VASP calculation in the unit cell setting {{TAG|LEPSILON}} or {{TAG|LCALCEPS}}.
 Optionally, specify a reciprocal space cutoff radius ({{TAG|PHON_G_CUTOFF}}) for the Ewald summation.
 ==Related tags and articles==

Mani: Use TAGO template

2024-02-23T12:29:31Z

Use TAGO template

← Older revision		Revision as of 12:29, 23 February 2024
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	== Polar materials ==		== Polar materials ==
	If the material is polar, i.e., two or more atoms in the unit cell carry non-zero Born effective charge tensors, the long-range dipole-dipole interaction has to be treated by [[Phonons:_Theory#Long-range_interatomic_force_constants_.28LO-TO_splitting.29\|Ewald summation]].		If the material is polar, i.e., two or more atoms in the unit cell carry non-zero Born effective charge tensors, the long-range dipole-dipole interaction has to be treated by [[Phonons:_Theory#Long-range_interatomic_force_constants_.28LO-TO_splitting.29\|Ewald summation]].
	This is achieved by setting {{~~TAG~~\|LPHON_POLAR}}~~=.TRUE.~~, supplying the static dielectric tensor ({{TAG\|PHON_DIELECTRIC}}) and the Born-effective charges ({{TAG\|PHON_BORN_CHARGES}}).		This is achieved by setting {{TAGO\|LPHON_POLAR\|True}}, supplying the static dielectric tensor ({{TAG\|PHON_DIELECTRIC}}) and the Born-effective charges ({{TAG\|PHON_BORN_CHARGES}}).
	The values for these have to be obtained from a separate VASP calculation in the unit cell setting {{TAG\|LEPSILON}} or {{TAG\|LCALCEPS}}.		The values for these have to be obtained from a separate VASP calculation in the unit cell setting {{TAG\|LEPSILON}} or {{TAG\|LCALCEPS}}.
	Optionally, specify a reciprocal space cutoff radius ({{TAG\|PHON_G_CUTOFF}}) for the Ewald summation.		Optionally, specify a reciprocal space cutoff radius ({{TAG\|PHON_G_CUTOFF}}) for the Ewald summation.

Huebsch: /* Phonon dispersion: Step-by-step instructions */

2024-02-20T09:14:46Z

Phonon dispersion: Step-by-step instructions

← Older revision		Revision as of 09:14, 20 February 2024
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	However, generating the finite displacements in the supercell to compute force constants is time-consuming.		However, generating the finite displacements in the supercell to compute force constants is time-consuming.
	It is possible to skip that step by providing force constants from a previous run.		It is possible to skip that step by providing force constants from a previous run.
	Rename the ~~<tt>~~vaspout.h5~~</tt>~~ output file from the previous calculation to ~~<tt>~~vaspin.h5~~</tt>~~, set		Rename the {{FILE\|vaspout.h5}} output file from the previous calculation to {{FILE\|vaspin.h5}}, set
	{{TAGBL\|LPHON_READ_FORCE_CONSTANTS}} = True		{{TAGBL\|LPHON_READ_FORCE_CONSTANTS}} = True
	{{TAGBL\|LPHON_DISPERSION}} = True		{{TAGBL\|LPHON_DISPERSION}} = True

← Older revision		Revision as of 08:01, 24 October 2025
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	=== Step 1: Compute the force constants ===		=== Step 1: Compute the force constants ===
	There are two possible approaches for computing the force constants and then building the dynamical matrix:		There are two possible approaches for computing the force constants and then building the dynamical matrix:
	# Using [[Phonons_from_finite_differences\|finite differences]] with {{~~TAGO~~\|IBRION\|5, 6}}.		# Using [[Phonons_from_finite_differences\|finite differences]] with {{TAG\|IBRION\|5, 6}}.
	# Using [[Phonons_from_density-functional-perturbation_theory\|DFPT]] with {{~~TAGO~~\|IBRION\|7, 8}}.		# Using [[Phonons_from_density-functional-perturbation_theory\|DFPT]] with {{TAG\|IBRION\|7, 8}}.
	These calculations must be performed in a supercell so that the force constants vanish at large distances.		These calculations must be performed in a supercell so that the force constants vanish at large distances.
	{{NB\|important\|The phonon frequencies need to be converged with respect to the supercell size.}}		{{NB\|important\|The phonon frequencies need to be converged with respect to the supercell size.}}
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	=== Step 3: Compute the phonon dispersion ===		=== Step 3: Compute the phonon dispersion ===

	To compute the phonon dispersion, set {{~~TAGO~~\|LPHON_DISPERSION\|true}} in the {{FILE\|INCAR}} file.		To compute the phonon dispersion, set {{TAG\|LPHON_DISPERSION\|true}} in the {{FILE\|INCAR}} file.
	The amount of information written to the {{FILE\|OUTCAR}} file can be tuned using the {{TAG\|PHON_NWRITE}} tag.		The amount of information written to the {{FILE\|OUTCAR}} file can be tuned using the {{TAG\|PHON_NWRITE}} tag.

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	=== Step 1: Compute the force constants ===		=== Step 1: Compute the force constants ===
	Same as [[#Phonon dispersion: Step-by-step instructions#Step 1: Compute the force constants\|above]].		Same as [[#Phonon dispersion: Step-by-step instructions#Step 1: Compute the force constants\|above]].
	This can be skipped by providing force constants in {{FILE\|vaspin.h5}} and setting {{~~TAGO~~\|LPHON_READ_FORCE_CONSTANTS\|True}}.		This can be skipped by providing force constants in {{FILE\|vaspin.h5}} and setting {{TAG\|LPHON_READ_FORCE_CONSTANTS\|True}}.

	=== Step 2: Specify a uniform '''q'''-point mesh ===		=== Step 2: Specify a uniform '''q'''-point mesh ===
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	=== Step 3: Compute the DOS ===		=== Step 3: Compute the DOS ===

	Set {{~~TAGO~~\|PHON_DOS\|0\|op=>}} in the {{FILE\|INCAR}} file. The DOS is computed between		Set {{TAG\|PHON_DOS\|0\|op=>}} in the {{FILE\|INCAR}} file. The DOS is computed between
	<math>[\omega_{\text{min}}-5\sigma,\omega_{\text{max}}+5\sigma]</math> with		<math>[\omega_{\text{min}}-5\sigma,\omega_{\text{max}}+5\sigma]</math> with
	<math>\omega_{\text{min}}</math> and		<math>\omega_{\text{min}}</math> and
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	<math>\sigma</math> the broadening ({{TAG\|PHON_SIGMA}}).		<math>\sigma</math> the broadening ({{TAG\|PHON_SIGMA}}).

	The number of energy points in this energy range is specified by the {{TAG\|PHON_NEDOS}} tag. To use a Gaussian-smearing method for the computation of the DOS set {{~~TAGO~~\|PHON_DOS\|1}} or to use the tetrahedron method set {{~~TAGO~~\|PHON_DOS\|2}}.		The number of energy points in this energy range is specified by the {{TAG\|PHON_NEDOS}} tag. To use a Gaussian-smearing method for the computation of the DOS set {{TAG\|PHON_DOS\|1}} or to use the tetrahedron method set {{TAG\|PHON_DOS\|2}}.

	== Polar materials ==		== Polar materials ==

	If the material is polar, i.e., two or more atoms in the unit cell carry non-zero Born effective charge tensors, the long-range dipole-dipole interaction has to be treated by [[Phonons:_Theory#Long-range_interatomic_force_constants_.28LO-TO_splitting.29\|Ewald summation]].		If the material is polar, i.e., two or more atoms in the unit cell carry non-zero Born effective charge tensors, the long-range dipole-dipole interaction has to be treated by [[Phonons:_Theory#Long-range_interatomic_force_constants_.28LO-TO_splitting.29\|Ewald summation]].
	This is achieved by setting {{~~TAGO~~\|LPHON_POLAR\|True}}, supplying the static dielectric tensor ({{TAG\|PHON_DIELECTRIC}}) and the Born-effective charges ({{TAG\|PHON_BORN_CHARGES}}).		This is achieved by setting {{TAG\|LPHON_POLAR\|True}}, supplying the static dielectric tensor ({{TAG\|PHON_DIELECTRIC}}) and the Born-effective charges ({{TAG\|PHON_BORN_CHARGES}}).
	The values for these dielectric properties have to be obtained from a separate VASP calculation in the unit cell setting {{TAG\|LEPSILON}} or {{TAG\|LCALCEPS}}.		The values for these dielectric properties have to be obtained from a separate VASP calculation in the unit cell setting {{TAG\|LEPSILON}} or {{TAG\|LCALCEPS}}.
	{{NB\|important\|Make sure to properly converge this unit-cell calculation with respect to the k-point mesh ({{FILE\|KPOINTS}}) and the electronic cutoff energy ({{TAG\|ENCUT}}) since the optical phonon frequencies depend strongly on the dielectric properties.}}		{{NB\|important\|Make sure to properly converge this unit-cell calculation with respect to the k-point mesh ({{FILE\|KPOINTS}}) and the electronic cutoff energy ({{TAG\|ENCUT}}) since the optical phonon frequencies depend strongly on the dielectric properties.}}
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	[[Image:AlN-phonons-LR-comparison.png\|400px\|thumb\|Phonon dispersion relation of AlN (wurtzite) comparing calculations with and without long-range (LR) dipole corrections. Notice the discontinuities around the Γ-point.]]		[[Image:AlN-phonons-LR-comparison.png\|400px\|thumb\|Phonon dispersion relation of AlN (wurtzite) comparing calculations with and without long-range (LR) dipole corrections. Notice the discontinuities around the Γ-point.]]
	As described on the [[Phonons:_Theory#Long-range_interatomic_force_constants_.28LO-TO_splitting.29\|theory page]], the presence of long-range electrostatic interactions leads to the splitting of the longitudinal optical (LO) from the transverse optical (TO) phonon modes.		As described on the [[Phonons:_Theory#Long-range_interatomic_force_constants_.28LO-TO_splitting.29\|theory page]], the presence of long-range electrostatic interactions leads to the splitting of the longitudinal optical (LO) from the transverse optical (TO) phonon modes.
	Once the required dielectric properties are provided and {{~~TAGO~~\|LPHON_POLAR\|True}} is set, VASP automatically considers the long-range dipole-dipole contributions to the interatomic force constants for phonon calculations.		Once the required dielectric properties are provided and {{TAG\|LPHON_POLAR\|True}} is set, VASP automatically considers the long-range dipole-dipole contributions to the interatomic force constants for phonon calculations.

	To illustrate the importance of long-range dipole corrections, we show two calculations of phonons in polar materials with strong LO-TO splitting.		To illustrate the importance of long-range dipole corrections, we show two calculations of phonons in polar materials with strong LO-TO splitting.