LTRIPLET - Revision history

Ftran at 08:25, 20 October 2023

2023-10-20T08:25:33Z

← Older revision		Revision as of 08:25, 20 October 2023
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	<references/>		<references/>
	----		----
	~~[[The_VASP_Manual\|Contents]]~~

	[[Category:INCAR tag]][[Category:Many-body perturbation theory]][[Category:Bethe-Salpeter equations]]		[[Category:INCAR tag]][[Category:Many-body perturbation theory]][[Category:Bethe-Salpeter equations]]

Huebsch: Huebsch moved page Construction:LTRIPLET to LTRIPLET

2022-04-07T12:21:12Z

Huebsch moved page Construction:LTRIPLET to LTRIPLET

← Older revision	Revision as of 12:21, 7 April 2022
(No difference)

Huebsch at 12:21, 7 April 2022

2022-04-07T12:21:03Z

← Older revision		Revision as of 12:21, 7 April 2022
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	{{DEF\|LTRIPLET\|.FALSE.\|}}		{{DEF\|LTRIPLET\|.FALSE.\|}}

	Description: {{TAG\|LTRIPLET}} selects a triplet ansatz for Bethe-~~Salpether~~-~~Equation~~ (BSE) calculations. This is ~~entirely~~ synonymous to {{TAG\|LHARTREE}} = .FALSE.		Description: {{TAG\|LTRIPLET}} selects a triplet ansatz for [[:Category:Bethe-Salpeter equations\|Bethe-Salpeter-equations]] (BSE) calculations. This is synonymous to {{TAG\|LHARTREE}} = .FALSE.
	----		----

	For a usual BSE calculation ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), the excited state corresponds to a singlet if the ground state is not spin-polarized ({{TAG\|ISPIN}}=1) or anti-ferromagnetic ({{TAG\|ISPIN}}=2, total magnetic moment 0). This is so because the ansatz for the BSE calculation involves a hole and an electron pair prepared within each spin channel. For instance, an electron with up spin is removed from the ground-state determinant and placed with the same spin into a previously unoccupied orbital. If there are no separate spin channels this ansatz results in a net spin zero, which corresponds to a singlet state.		For a usual BSE calculation ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), the excited state corresponds to a singlet if the ground state is not spin-polarized ({{TAG\|ISPIN}}=1) or anti-ferromagnetic ({{TAG\|ISPIN}}=2, total magnetic moment 0). This is so because the ansatz for the BSE calculation involves a hole and an electron pair prepared within each spin channel. For instance, an electron with up spin is removed from the ground-state determinant and placed with the same spin into a previously unoccupied orbital. If there are no separate spin channels this ansatz results in a net spin-zero, which corresponds to a singlet state.

	If {{TAG\|LTRIPLET}}=.TRUE., VASP assumes that an ''up'' electron is removed from the ground-state determinant and placed as a ''down'' electron into a previously unoccupied orbital (spin flip). This ansatz corresponds to a triplet state as it has a net spin of one. Without spin-orbit coupling ({{TAG\|LSORBIT}} = .FALSE.), the transition probability from the singlet ground state to the triplet solutions will be exactly zero. These excitations correspond to dark, potentially long-lived triplet excitons. However, VASP calculates the transition probabilities incorrectly, by assuming that a spin flip excitation has the same transition probabilities as ~~for~~ a usual singlet excitation.		If {{TAG\|LTRIPLET}}=.TRUE., VASP assumes that an ''up'' electron is removed from the ground-state determinant and placed as a ''down'' electron into a previously unoccupied orbital (spin flip). This ansatz corresponds to a triplet state as it has a net spin of one. Without spin-orbit coupling ({{TAG\|LSORBIT}} = .FALSE.), the transition probability from the singlet ground state to the triplet solutions will be exactly zero. These excitations correspond to dark, potentially long-lived triplet excitons. However, VASP calculates the transition probabilities incorrectly, by assuming that a spin-flip excitation has the same transition probabilities as a usual singlet excitation.
	The reported transition probabilities ("~~opticaltransitions~~" in {{TAG\|vasprun.xml}}) are hence incorrect; they should be all zero. Likewise, the contributions to the dielectric function are zero for triplet excitations,		The reported transition probabilities ("optical transitions" in {{TAG\|vasprun.xml}}) are hence incorrect; they should be all zero. Likewise, the contributions to the dielectric function are zero for triplet excitations,
	and incorrectly reported in the {{TAG\|vasprun.xml}} file.		and incorrectly reported in the {{TAG\|vasprun.xml}} file.

Line 14:		Line 14:
	singlet transitions as well as one set of the triplet excitations (those with <math> m_S=0</math> ) are calculated. All triplet transitions will have zero transition probabilities. If {{TAG\|LTRIPLET}} = .TRUE. is set for the BSE calculation, the other two sets of triplet excitations (those with <math> m_S=1</math> and <math> m_S=-1</math>) are determined. Note that as for {{TAG\|ISPIN}}=1 for {{TAG\|ISPIN}}=2 and {{TAG\|LTRIPLET}} = .FALSE., incorrect non-zero transition probabilities are reported in the {{TAG\|vasprun.xml}} file (they should be all exactly zero, since the underlying pair states fed into the BSE can not be excited by light).		singlet transitions as well as one set of the triplet excitations (those with <math> m_S=0</math> ) are calculated. All triplet transitions will have zero transition probabilities. If {{TAG\|LTRIPLET}} = .TRUE. is set for the BSE calculation, the other two sets of triplet excitations (those with <math> m_S=1</math> and <math> m_S=-1</math>) are determined. Note that as for {{TAG\|ISPIN}}=1 for {{TAG\|ISPIN}}=2 and {{TAG\|LTRIPLET}} = .FALSE., incorrect non-zero transition probabilities are reported in the {{TAG\|vasprun.xml}} file (they should be all exactly zero, since the underlying pair states fed into the BSE can not be excited by light).

	To obtain meaningful transition probabilities for the singlet and triplet excitations, spin-orbit coupling ~~should be included~~ by setting {{TAG\|LSORBIT}} = .TRUE. in the {{FILE\|INCAR}} file throughout the calculation, i.e., for the ground-state and BSE calculation. In this case, the singlet and all three sets of triplet excitations are calculated simultaneously, and proper transition probabilities are assigned to each transition. Small transition ~~probabilties~~ might		To obtain meaningful transition probabilities for the singlet and triplet excitations, include spin-orbit coupling by setting {{TAG\|LSORBIT}} = .TRUE. in the {{FILE\|INCAR}} file throughout the calculation, i.e., for the ground-state and BSE calculation. In this case, the singlet and all three sets of triplet excitations are calculated simultaneously, and proper transition probabilities are assigned to each transition. Small transition probabilities might be observed even for triplet excitations as a result of spin-orbit coupling. {{TAG\|LTRIPLET}} = .TRUE. should not be used for calculations including spin-orbit coupling.
	be observed even for triplet excitations as a result of spin orbit coupling. {{TAG\|LTRIPLET}} = .TRUE. should not be used for calculations including spin orbit coupling.

	{{NB\|warning\| {{TAG\|LTRIPLET}}{{=}}.TRUE. has not been extensively tested in combination with spin-polarized ground states ({{TAG\|ISPIN}}{{=}}2).}}		{{NB\|warning\| {{TAG\|LTRIPLET}}{{=}}.TRUE. has not been extensively tested in combination with spin-polarized ground states ({{TAG\|ISPIN}}{{=}}2).}}
	{{NB\|warning\| ~~Not~~ sure whether the [[BSEFATBAND]] approach can be combined with the {{TAG\|LTRIPLET}} tag.}}		{{NB\|warning\| We are not sure whether the [[BSEFATBAND]] approach can be combined with the {{TAG\|LTRIPLET}} tag.}}

	== Related tags and articles==		== Related tags and articles==
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	[[The_VASP_Manual\|Contents]]		[[The_VASP_Manual\|Contents]]

	[[Category:INCAR]][[Category:~~BSE~~]]		[[Category:INCAR tag]][[Category:Many-body perturbation theory]][[Category:Bethe-Salpeter equations]]

Kresse at 16:49, 12 January 2022

2022-01-12T16:49:33Z

← Older revision		Revision as of 16:49, 12 January 2022
Line 12:		Line 12:

	If a non-magnetic material is calculated using {{TAG\|ISPIN}}=2 for both the groundstate and BSE calculation, and a usual BSE calculation is performed ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), all		If a non-magnetic material is calculated using {{TAG\|ISPIN}}=2 for both the groundstate and BSE calculation, and a usual BSE calculation is performed ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), all
	singlet transitions as well as one set of the triplet excitations (those with <math> m_S=0</math> ) are calculated. All triplet transitions will have zero transition probabilities. If {{TAG\|LTRIPLET}} = .TRUE. is set for the BSE calculation, the other two sets of triplet excitations (those with <math> m_S=1</math> and <math> m_S=-1</math>) are determined. Note that as for {{TAG\|ISPIN}}=1 for {{TAG\|ISPIN}}=2 and {{TAG\|LTRIPLET}} = .FALSE., incorrect non-zero transition probabilities are reported in the {{TAG\|vasprun.xml}} file (they should be all exactly zero).		singlet transitions as well as one set of the triplet excitations (those with <math> m_S=0</math> ) are calculated. All triplet transitions will have zero transition probabilities. If {{TAG\|LTRIPLET}} = .TRUE. is set for the BSE calculation, the other two sets of triplet excitations (those with <math> m_S=1</math> and <math> m_S=-1</math>) are determined. Note that as for {{TAG\|ISPIN}}=1 for {{TAG\|ISPIN}}=2 and {{TAG\|LTRIPLET}} = .FALSE., incorrect non-zero transition probabilities are reported in the {{TAG\|vasprun.xml}} file (they should be all exactly zero, since the underlying pair states fed into the BSE can not be excited by light).

	To obtain meaningful transition probabilities for the singlet and triplet excitations, spin-orbit coupling should be included by setting {{TAG\|LSORBIT}} = .TRUE. in the {{FILE\|INCAR}} file throughout the calculation, i.e., for the ground-state and BSE calculation. In this case, the singlet and all three sets of triplet excitations are calculated simultaneously, and proper transition probabilities are assigned to each transition. Small transition probabilties might		To obtain meaningful transition probabilities for the singlet and triplet excitations, spin-orbit coupling should be included by setting {{TAG\|LSORBIT}} = .TRUE. in the {{FILE\|INCAR}} file throughout the calculation, i.e., for the ground-state and BSE calculation. In this case, the singlet and all three sets of triplet excitations are calculated simultaneously, and proper transition probabilities are assigned to each transition. Small transition probabilties might

Kresse: Small corrections, and comment on LTRIPLET added for spin orbit coupling.

2022-01-12T07:13:47Z

Small corrections, and comment on LTRIPLET added for spin orbit coupling.

← Older revision		Revision as of 07:13, 12 January 2022
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	----		----

	For a usual BSE calculation ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), the excited state corresponds to a singlet if the ground state is not spin-polarized ({{TAG\|ISPIN}}=1) or anti-ferromagnetic ({{TAG\|ISPIN}}=2, total magnetic moment 0). ~~That~~ is because the ansatz for the BSE calculation involves a hole and an electron pair prepared within each spin channel. For instance, an electron with up spin is removed from the ground-state determinant and placed with the same spin into a previously unoccupied orbital. If there are no separate spin channels this ansatz results in a net spin zero, which corresponds to a singlet state.		For a usual BSE calculation ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), the excited state corresponds to a singlet if the ground state is not spin-polarized ({{TAG\|ISPIN}}=1) or anti-ferromagnetic ({{TAG\|ISPIN}}=2, total magnetic moment 0). This is so because the ansatz for the BSE calculation involves a hole and an electron pair prepared within each spin channel. For instance, an electron with up spin is removed from the ground-state determinant and placed with the same spin into a previously unoccupied orbital. If there are no separate spin channels this ansatz results in a net spin zero, which corresponds to a singlet state.

	If {{TAG\|LTRIPLET}}=.TRUE., VASP assumes that an ''up'' electron is removed from the ground-state determinant and placed as a ''down'' electron into a previously unoccupied orbital (spin flip). This ansatz corresponds to a triplet state as it has a net spin of one. Without spin-orbit coupling ({{TAG\|LSORBIT}} = .FALSE.), the transition probability from singlet ground state to the triplet solutions will be exactly zero. These excitations correspond to dark, potentially long-lived triplet excitons. However, VASP calculates the transition probabilities incorrectly, by assuming that a spin flip excitation has the same transition probabilities as for a usual singlet excitation.		If {{TAG\|LTRIPLET}}=.TRUE., VASP assumes that an ''up'' electron is removed from the ground-state determinant and placed as a ''down'' electron into a previously unoccupied orbital (spin flip). This ansatz corresponds to a triplet state as it has a net spin of one. Without spin-orbit coupling ({{TAG\|LSORBIT}} = .FALSE.), the transition probability from the singlet ground state to the triplet solutions will be exactly zero. These excitations correspond to dark, potentially long-lived triplet excitons. However, VASP calculates the transition probabilities incorrectly, by assuming that a spin flip excitation has the same transition probabilities as for a usual singlet excitation.
	The reported transition probabilities ("opticaltransitions" in {{TAG\|vasprun.xml}}) are hence incorrect, they should be all zero. Likewise, the contributions to the dielectric function are zero for triplet excitations,		The reported transition probabilities ("opticaltransitions" in {{TAG\|vasprun.xml}}) are hence incorrect; they should be all zero. Likewise, the contributions to the dielectric function are zero for triplet excitations,
	and incorrectly reported in the {{TAG\|vasprun.xml}} file.		and incorrectly reported in the {{TAG\|vasprun.xml}} file.


	If a non-magnetic material is calculated using {{TAG\|ISPIN}}=2 for both the groundstate and BSE calculation, and a usual BSE calculation is performed ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), all		If a non-magnetic material is calculated using {{TAG\|ISPIN}}=2 for both the groundstate and BSE calculation, and a usual BSE calculation is performed ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), all
	singlet transitions as well as one set of the triplet excitations (those with <math> m_S=0</math> ) are calculated. All triplet transitions will have zero transition probabilities. If {{TAG\|LTRIPLET}} = .TRUE. is set for the BSE calculation, the other two sets of triplet excitations (those with <math> m_S=1</math> and <math> m_S=-1</math>) are determined. Note that as for {{TAG\|ISPIN}}=1 for {{TAG\|ISPIN}}=2 and {{TAG\|LTRIPLET}} = .FALSE., incorrect non-zero transition probabilities are reported in the {{TAG\|vasprun.xml}} file (they should be all exactly zero).		singlet transitions as well as one set of the triplet excitations (those with <math> m_S=0</math> ) are calculated. All triplet transitions will have zero transition probabilities. If {{TAG\|LTRIPLET}} = .TRUE. is set for the BSE calculation, the other two sets of triplet excitations (those with <math> m_S=1</math> and <math> m_S=-1</math>) are determined. Note that as for {{TAG\|ISPIN}}=1 for {{TAG\|ISPIN}}=2 and {{TAG\|LTRIPLET}} = .FALSE., incorrect non-zero transition probabilities are reported in the {{TAG\|vasprun.xml}} file (they should be all exactly zero).

	To obtain meaningful transition probabilities for the singlet and triplet excitations, spin-orbit coupling should be included by setting {{TAG\|LSORBIT}} = .TRUE. in the {{FILE\|INCAR}} file throughout the calculation, i.e., for the ground-state and BSE calculation. In this case, the singlet and all three sets of triplet excitations are calculated simultaneously, and proper transition probabilities are assigned to each transition. Small transition ~~propabilties~~ might		To obtain meaningful transition probabilities for the singlet and triplet excitations, spin-orbit coupling should be included by setting {{TAG\|LSORBIT}} = .TRUE. in the {{FILE\|INCAR}} file throughout the calculation, i.e., for the ground-state and BSE calculation. In this case, the singlet and all three sets of triplet excitations are calculated simultaneously, and proper transition probabilities are assigned to each transition. Small transition probabilties might
	be ~~visible~~ even for triplet excitations as a result of spin orbit coupling.		be observed even for triplet excitations as a result of spin orbit coupling. {{TAG\|LTRIPLET}} = .TRUE. should not be used for calculations including spin orbit coupling.

	{{NB\|warning\| {{TAG\|LTRIPLET}}{{=}}.TRUE. has not been extensively tested in combination with spin-polarized ground states ({{TAG\|ISPIN}}{{=}}2).}}		{{NB\|warning\| {{TAG\|LTRIPLET}}{{=}}.TRUE. has not been extensively tested in combination with spin-polarized ground states ({{TAG\|ISPIN}}{{=}}2).}}

Kresse at 14:58, 11 January 2022

2022-01-11T14:58:11Z

← Older revision		Revision as of 14:58, 11 January 2022
Line 11:		Line 11:
	and incorrectly reported in the {{TAG\|vasprun.xml}} file.		and incorrectly reported in the {{TAG\|vasprun.xml}} file.

	To obtain accurate meaningful transition probabilities for the singlet and triplet excitations, spin-orbit coupling should be included by setting {{TAG\|LSORBIT}} = .TRUE. in the {{FILE\|INCAR}} file throughout the calculation, i.e., for the ground-state and BSE calculation. In this case, the singlet and triplet excitations are calculated all simultaneously, and proper transition probabilities are assigned to each transition.

	If a non-magnetic material is calculated using {{TAG\|ISPIN}}=2 for both the groundstate and BSE calculation, and a usual BSE calculation is performed ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), ~~the~~		If a non-magnetic material is calculated using {{TAG\|ISPIN}}=2 for both the groundstate and BSE calculation, and a usual BSE calculation is performed ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), all
	singlet as well as one set of the triplet excitations (~~that~~ with <math> m_S=0</math> ) is calculated. If {{TAG\|LTRIPLET}} = .TRUE. is set for the BSE calculation, the other two sets of triplet excitations (those with <math> m_S=1</math> and <math> m_S=-1</math>) are determined. Note that ~~again~~ for {{TAG\|LTRIPLET}} = .FALSE., incorrect non-zero transition ~~propabilties~~ are reported in the {{TAG\|vasprun.xml}} file (they should be all zero).		singlet transitions as well as one set of the triplet excitations (those with <math> m_S=0</math> ) are calculated. All triplet transitions will have zero transition probabilities. If {{TAG\|LTRIPLET}} = .TRUE. is set for the BSE calculation, the other two sets of triplet excitations (those with <math> m_S=1</math> and <math> m_S=-1</math>) are determined. Note that as for {{TAG\|ISPIN}}=1 for {{TAG\|ISPIN}}=2 and {{TAG\|LTRIPLET}} = .FALSE., incorrect non-zero transition probabilities are reported in the {{TAG\|vasprun.xml}} file (they should be all exactly zero).

			To obtain meaningful transition probabilities for the singlet and triplet excitations, spin-orbit coupling should be included by setting {{TAG\|LSORBIT}} = .TRUE. in the {{FILE\|INCAR}} file throughout the calculation, i.e., for the ground-state and BSE calculation. In this case, the singlet and all three sets of triplet excitations are calculated simultaneously, and proper transition probabilities are assigned to each transition. Small transition propabilties might
			be visible even for triplet excitations as a result of spin orbit coupling.

	For a BSE calculation ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.) based on a spin-polarized ground-state calculation ({{TAG\|ISPIN}}=2), VASP yields one set of singlet solutions and one set of triplet solutions. With {{TAG\|LTRIPLET}}=.TRUE., VASP will obtain the remaining two sets of triplet solutions.
	{{NB\|warning\| {{TAG\|LTRIPLET}}{{=}}.TRUE. has not been extensively tested in combination with spin-polarized ground states ({{TAG\|ISPIN}}{{=}}2).}}		{{NB\|warning\| {{TAG\|LTRIPLET}}{{=}}.TRUE. has not been extensively tested in combination with spin-polarized ground states ({{TAG\|ISPIN}}{{=}}2).}}
	{{NB\|warning\| Not sure whether the [[BSEFATBAND]] approach can be combined with the {{TAG\|LTRIPLET}} tag.}}		{{NB\|warning\| Not sure whether the [[BSEFATBAND]] approach can be combined with the {{TAG\|LTRIPLET}} tag.}}

Kresse: Extended

2022-01-11T14:50:34Z

Extended

← Older revision		Revision as of 14:50, 11 January 2022
Line 2:		Line 2:
	{{DEF\|LTRIPLET\|.FALSE.\|}}		{{DEF\|LTRIPLET\|.FALSE.\|}}

	Description: {{TAG\|LTRIPLET}} selects a triplet ansatz for Bethe-Salpether-Equation (BSE) calculations.		Description: {{TAG\|LTRIPLET}} selects a triplet ansatz for Bethe-Salpether-Equation (BSE) calculations. This is entirely synonymous to {{TAG\|LHARTREE}} = .FALSE.
	----		----

	For a usual BSE calculation ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), the excited state corresponds to a singlet if the ground state is not spin-polarized ({{TAG\|ISPIN}}=1). That is because the ansatz for the BSE calculation involves a hole and an electron pair prepared within each spin channel. For instance, an electron with up spin is removed from the ground-state determinant and placed with the same spin into a previously unoccupied orbital. If there are no ~~seperate~~ spin channels this ansatz results in a net spin zero, which corresponds to a singlet state.		For a usual BSE calculation ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), the excited state corresponds to a singlet if the ground state is not spin-polarized ({{TAG\|ISPIN}}=1) or anti-ferromagnetic ({{TAG\|ISPIN}}=2, total magnetic moment 0). That is because the ansatz for the BSE calculation involves a hole and an electron pair prepared within each spin channel. For instance, an electron with up spin is removed from the ground-state determinant and placed with the same spin into a previously unoccupied orbital. If there are no separate spin channels this ansatz results in a net spin zero, which corresponds to a singlet state.

			If {{TAG\|LTRIPLET}}=.TRUE., VASP assumes that an ''up'' electron is removed from the ground-state determinant and placed as a ''down'' electron into a previously unoccupied orbital (spin flip). This ansatz corresponds to a triplet state as it has a net spin of one. Without spin-orbit coupling ({{TAG\|LSORBIT}} = .FALSE.), the transition probability from singlet ground state to the triplet solutions will be exactly zero. These excitations correspond to dark, potentially long-lived triplet excitons. However, VASP calculates the transition probabilities incorrectly, by assuming that a spin flip excitation has the same transition probabilities as for a usual singlet excitation.
			The reported transition probabilities ("opticaltransitions" in {{TAG\|vasprun.xml}}) are hence incorrect, they should be all zero. Likewise, the contributions to the dielectric function are zero for triplet excitations,
			and incorrectly reported in the {{TAG\|vasprun.xml}} file.

			To obtain accurate meaningful transition probabilities for the singlet and triplet excitations, spin-orbit coupling should be included by setting {{TAG\|LSORBIT}} = .TRUE. in the {{FILE\|INCAR}} file throughout the calculation, i.e., for the ground-state and BSE calculation. In this case, the singlet and triplet excitations are calculated all simultaneously, and proper transition probabilities are assigned to each transition.

			If a non-magnetic material is calculated using {{TAG\|ISPIN}}=2 for both the groundstate and BSE calculation, and a usual BSE calculation is performed ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), the
			singlet as well as one set of the triplet excitations (that with <math> m_S=0</math> ) is calculated. If {{TAG\|LTRIPLET}} = .TRUE. is set for the BSE calculation, the other two sets of triplet excitations (those with <math> m_S=1</math> and <math> m_S=-1</math>) are determined. Note that again for {{TAG\|LTRIPLET}} = .FALSE., incorrect non-zero transition propabilties are reported in the {{TAG\|vasprun.xml}} file (they should be all zero).

	If {{TAG\|LTRIPLET}}=.TRUE., VASP assumes that an ''up'' electron is removed from the ground-state determinant and places a ''down'' electron in a previously unoccupied orbital. This ansatz corresponds to a triplet state as it has a net spin one. Without spin-orbit coupling ({{TAG\|LSORBIT}} = .FALSE.), many (or maybe even all) of the triplet solutions will have zero transition probabilities. These correspond to dark, potentially long-lived triplet excitons. To obtain non-zero transition probabilities for the triplets, spin-orbit coupling should be included by setting {{TAG\|LSORBIT}} = .TRUE. in the {{FILE\|INCAR}} file throughout the calculation, i.e., also in the ground-state calculation.

	For a BSE calculation ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.) based on a spin-polarized ground-state calculation ({{TAG\|ISPIN}}=2), VASP yields one set of singlet solutions and one set of triplet solutions. With {{TAG\|LTRIPLET}}=.TRUE., VASP will obtain the remaining two sets of triplet solutions.		For a BSE calculation ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.) based on a spin-polarized ground-state calculation ({{TAG\|ISPIN}}=2), VASP yields one set of singlet solutions and one set of triplet solutions. With {{TAG\|LTRIPLET}}=.TRUE., VASP will obtain the remaining two sets of triplet solutions.

Huebsch: Created page with "{{TAGDEF|LTRIPLET|.TRUE. {{!}} .FALSE.}} {{DEF|LTRIPLET|.FALSE.|}} Description: {{TAG|LTRIPLET}} selects a triplet ansatz for Bethe-Salpether-Equation (BSE) calculations. ---..."

2022-01-10T16:19:05Z

Created page with "{{TAGDEF|LTRIPLET|.TRUE. {{!}} .FALSE.}} {{DEF|LTRIPLET|.FALSE.|}} Description: {{TAG|LTRIPLET}} selects a triplet ansatz for Bethe-Salpether-Equation (BSE) calculations. ---..."

New page

{{TAGDEF|LTRIPLET|.TRUE. {{!}} .FALSE.}}
{{DEF|LTRIPLET|.FALSE.|}}

Description: {{TAG|LTRIPLET}} selects a triplet ansatz for Bethe-Salpether-Equation (BSE) calculations.
----

For a usual BSE calculation ({{TAG|LHARTREE}}=.TRUE.; {{TAG|LTRIPLET}} = .FALSE.), the excited state corresponds to a singlet if the ground state is not spin-polarized ({{TAG|ISPIN}}=1). That is because the ansatz for the BSE calculation involves a hole and an electron pair prepared within each spin channel. For instance, an electron with up spin is removed from the ground-state determinant and placed with the same spin into a previously unoccupied orbital. If there are no seperate spin channels this ansatz results in a net spin zero, which corresponds to a singlet state.

If {{TAG|LTRIPLET}}=.TRUE., VASP assumes that an ''up'' electron is removed from the ground-state determinant and places a ''down'' electron in a previously unoccupied orbital. This ansatz corresponds to a triplet state as it has a net spin one. Without spin-orbit coupling ({{TAG|LSORBIT}} = .FALSE.), many (or maybe even all) of the triplet solutions will have zero transition probabilities. These correspond to dark, potentially long-lived triplet excitons. To obtain non-zero transition probabilities for the triplets, spin-orbit coupling should be included by setting {{TAG|LSORBIT}} = .TRUE. in the {{FILE|INCAR}} file throughout the calculation, i.e., also in the ground-state calculation.

For a BSE calculation ({{TAG|LHARTREE}}=.TRUE.; {{TAG|LTRIPLET}} = .FALSE.) based on a spin-polarized ground-state calculation ({{TAG|ISPIN}}=2), VASP yields one set of singlet solutions and one set of triplet solutions. With {{TAG|LTRIPLET}}=.TRUE., VASP will obtain the remaining two sets of triplet solutions.
{{NB|warning| {{TAG|LTRIPLET}}{{=}}.TRUE. has not been extensively tested in combination with spin-polarized ground states ({{TAG|ISPIN}}{{=}}2).}}
{{NB|warning| Not sure whether the [[BSEFATBAND]] approach can be combined with the {{TAG|LTRIPLET}} tag.}}

== Related tags and articles==
{{TAG|LHARTREE}},
{{TAG|ISPIN}},
{{TAG|LSORBIT}},
[[BSE calculations]]

{{sc|LTRIPLET|Examples|Examples that use this tag}}

== References ==
<references/>
----
[[The_VASP_Manual|Contents]]

[[Category:INCAR]][[Category:BSE]]

← Older revision		Revision as of 16:49, 12 January 2022
Line 12:		Line 12:

	If a non-magnetic material is calculated using {{TAG\|ISPIN}}=2 for both the groundstate and BSE calculation, and a usual BSE calculation is performed ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), all		If a non-magnetic material is calculated using {{TAG\|ISPIN}}=2 for both the groundstate and BSE calculation, and a usual BSE calculation is performed ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), all
	singlet transitions as well as one set of the triplet excitations (those with <math> m_S=0</math> ) are calculated. All triplet transitions will have zero transition probabilities. If {{TAG\|LTRIPLET}} = .TRUE. is set for the BSE calculation, the other two sets of triplet excitations (those with <math> m_S=1</math> and <math> m_S=-1</math>) are determined. Note that as for {{TAG\|ISPIN}}=1 for {{TAG\|ISPIN}}=2 and {{TAG\|LTRIPLET}} = .FALSE., incorrect non-zero transition probabilities are reported in the {{TAG\|vasprun.xml}} file (they should be all exactly zero).		singlet transitions as well as one set of the triplet excitations (those with <math> m_S=0</math> ) are calculated. All triplet transitions will have zero transition probabilities. If {{TAG\|LTRIPLET}} = .TRUE. is set for the BSE calculation, the other two sets of triplet excitations (those with <math> m_S=1</math> and <math> m_S=-1</math>) are determined. Note that as for {{TAG\|ISPIN}}=1 for {{TAG\|ISPIN}}=2 and {{TAG\|LTRIPLET}} = .FALSE., incorrect non-zero transition probabilities are reported in the {{TAG\|vasprun.xml}} file (they should be all exactly zero, since the underlying pair states fed into the BSE can not be excited by light).

	To obtain meaningful transition probabilities for the singlet and triplet excitations, spin-orbit coupling should be included by setting {{TAG\|LSORBIT}} = .TRUE. in the {{FILE\|INCAR}} file throughout the calculation, i.e., for the ground-state and BSE calculation. In this case, the singlet and all three sets of triplet excitations are calculated simultaneously, and proper transition probabilities are assigned to each transition. Small transition probabilties might		To obtain meaningful transition probabilities for the singlet and triplet excitations, spin-orbit coupling should be included by setting {{TAG\|LSORBIT}} = .TRUE. in the {{FILE\|INCAR}} file throughout the calculation, i.e., for the ground-state and BSE calculation. In this case, the singlet and all three sets of triplet excitations are calculated simultaneously, and proper transition probabilities are assigned to each transition. Small transition probabilties might

← Older revision		Revision as of 07:13, 12 January 2022
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	For a usual BSE calculation ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), the excited state corresponds to a singlet if the ground state is not spin-polarized ({{TAG\|ISPIN}}=1) or anti-ferromagnetic ({{TAG\|ISPIN}}=2, total magnetic moment 0). ~~That~~ is because the ansatz for the BSE calculation involves a hole and an electron pair prepared within each spin channel. For instance, an electron with up spin is removed from the ground-state determinant and placed with the same spin into a previously unoccupied orbital. If there are no separate spin channels this ansatz results in a net spin zero, which corresponds to a singlet state.		For a usual BSE calculation ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), the excited state corresponds to a singlet if the ground state is not spin-polarized ({{TAG\|ISPIN}}=1) or anti-ferromagnetic ({{TAG\|ISPIN}}=2, total magnetic moment 0). This is so because the ansatz for the BSE calculation involves a hole and an electron pair prepared within each spin channel. For instance, an electron with up spin is removed from the ground-state determinant and placed with the same spin into a previously unoccupied orbital. If there are no separate spin channels this ansatz results in a net spin zero, which corresponds to a singlet state.

	If {{TAG\|LTRIPLET}}=.TRUE., VASP assumes that an ''up'' electron is removed from the ground-state determinant and placed as a ''down'' electron into a previously unoccupied orbital (spin flip). This ansatz corresponds to a triplet state as it has a net spin of one. Without spin-orbit coupling ({{TAG\|LSORBIT}} = .FALSE.), the transition probability from singlet ground state to the triplet solutions will be exactly zero. These excitations correspond to dark, potentially long-lived triplet excitons. However, VASP calculates the transition probabilities incorrectly, by assuming that a spin flip excitation has the same transition probabilities as for a usual singlet excitation.		If {{TAG\|LTRIPLET}}=.TRUE., VASP assumes that an ''up'' electron is removed from the ground-state determinant and placed as a ''down'' electron into a previously unoccupied orbital (spin flip). This ansatz corresponds to a triplet state as it has a net spin of one. Without spin-orbit coupling ({{TAG\|LSORBIT}} = .FALSE.), the transition probability from the singlet ground state to the triplet solutions will be exactly zero. These excitations correspond to dark, potentially long-lived triplet excitons. However, VASP calculates the transition probabilities incorrectly, by assuming that a spin flip excitation has the same transition probabilities as for a usual singlet excitation.
	The reported transition probabilities ("opticaltransitions" in {{TAG\|vasprun.xml}}) are hence incorrect, they should be all zero. Likewise, the contributions to the dielectric function are zero for triplet excitations,		The reported transition probabilities ("opticaltransitions" in {{TAG\|vasprun.xml}}) are hence incorrect; they should be all zero. Likewise, the contributions to the dielectric function are zero for triplet excitations,
	and incorrectly reported in the {{TAG\|vasprun.xml}} file.		and incorrectly reported in the {{TAG\|vasprun.xml}} file.


	If a non-magnetic material is calculated using {{TAG\|ISPIN}}=2 for both the groundstate and BSE calculation, and a usual BSE calculation is performed ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), all		If a non-magnetic material is calculated using {{TAG\|ISPIN}}=2 for both the groundstate and BSE calculation, and a usual BSE calculation is performed ({{TAG\|LHARTREE}}=.TRUE.; {{TAG\|LTRIPLET}} = .FALSE.), all
	singlet transitions as well as one set of the triplet excitations (those with <math> m_S=0</math> ) are calculated. All triplet transitions will have zero transition probabilities. If {{TAG\|LTRIPLET}} = .TRUE. is set for the BSE calculation, the other two sets of triplet excitations (those with <math> m_S=1</math> and <math> m_S=-1</math>) are determined. Note that as for {{TAG\|ISPIN}}=1 for {{TAG\|ISPIN}}=2 and {{TAG\|LTRIPLET}} = .FALSE., incorrect non-zero transition probabilities are reported in the {{TAG\|vasprun.xml}} file (they should be all exactly zero).		singlet transitions as well as one set of the triplet excitations (those with <math> m_S=0</math> ) are calculated. All triplet transitions will have zero transition probabilities. If {{TAG\|LTRIPLET}} = .TRUE. is set for the BSE calculation, the other two sets of triplet excitations (those with <math> m_S=1</math> and <math> m_S=-1</math>) are determined. Note that as for {{TAG\|ISPIN}}=1 for {{TAG\|ISPIN}}=2 and {{TAG\|LTRIPLET}} = .FALSE., incorrect non-zero transition probabilities are reported in the {{TAG\|vasprun.xml}} file (they should be all exactly zero).

	To obtain meaningful transition probabilities for the singlet and triplet excitations, spin-orbit coupling should be included by setting {{TAG\|LSORBIT}} = .TRUE. in the {{FILE\|INCAR}} file throughout the calculation, i.e., for the ground-state and BSE calculation. In this case, the singlet and all three sets of triplet excitations are calculated simultaneously, and proper transition probabilities are assigned to each transition. Small transition ~~propabilties~~ might		To obtain meaningful transition probabilities for the singlet and triplet excitations, spin-orbit coupling should be included by setting {{TAG\|LSORBIT}} = .TRUE. in the {{FILE\|INCAR}} file throughout the calculation, i.e., for the ground-state and BSE calculation. In this case, the singlet and all three sets of triplet excitations are calculated simultaneously, and proper transition probabilities are assigned to each transition. Small transition probabilties might
	be ~~visible~~ even for triplet excitations as a result of spin orbit coupling.		be observed even for triplet excitations as a result of spin orbit coupling. {{TAG\|LTRIPLET}} = .TRUE. should not be used for calculations including spin orbit coupling.

	{{NB\|warning\| {{TAG\|LTRIPLET}}{{=}}.TRUE. has not been extensively tested in combination with spin-polarized ground states ({{TAG\|ISPIN}}{{=}}2).}}		{{NB\|warning\| {{TAG\|LTRIPLET}}{{=}}.TRUE. has not been extensively tested in combination with spin-polarized ground states ({{TAG\|ISPIN}}{{=}}2).}}