Multireference configuration interaction - Revision history

Me, Myself, and I are Here: bold

2024-10-01T01:31:45Z

bold

← Previous revision		Revision as of 01:31, 1 October 2024
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	In [[quantum chemistry]], the '''multireference configuration interaction''' (MRCI) method consists of a [[configuration interaction]] expansion of the [[eigenstate]]s of the [[electronic molecular Hamiltonian]] in a set of [[Slater determinant]]s which correspond to excitations of the [[ground state]] [[electronic configuration]] but also of some [[excited state]]s. The Slater determinants from which the excitations are performed are called '''reference determinants'''. The higher excited determinants (also called [[configuration state function]]s (CSFs) or shortly configurations) are then chosen either by the program according to some [[perturbation theory\|perturbation theoretical]] [[ansatz]] according to a threshold provided by the user or simply by truncating excitations from these references to singly, doubly, ... excitations resulting in MRCIS, MRCISD, etc.		In [[quantum chemistry]], the '''multireference configuration interaction''' ('''MRCI''') method consists of a [[configuration interaction]] expansion of the [[eigenstate]]s of the [[electronic molecular Hamiltonian]] in a set of [[Slater determinant]]s which correspond to excitations of the [[ground state]] [[electronic configuration]] but also of some [[excited state]]s. The Slater determinants from which the excitations are performed are called '''reference determinants'''. The higher excited determinants (also called [[configuration state function]]s (CSFs) or shortly configurations) are then chosen either by the program according to some [[perturbation theory\|perturbation theoretical]] [[ansatz]] according to a threshold provided by the user or simply by truncating excitations from these references to singly, doubly, ... excitations resulting in MRCIS, MRCISD, etc.

	For the ground state using more than one reference configuration means a better [[electronic correlation\|correlation]] and so a lower energy. The problem of [[size consistency\|size inconsistency]] of truncated CI-methods is not solved by taking more references.		For the ground state using more than one reference configuration means a better [[electronic correlation\|correlation]] and so a lower energy. The problem of [[size consistency\|size inconsistency]] of truncated CI-methods is not solved by taking more references.

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2022-10-24T09:46:10Z

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← Previous revision		Revision as of 09:46, 24 October 2022
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	Selecting the references can be done manually (<math> \Phi_1, \Phi_2, \Phi_5, ...</math>), automatically (all possible configurations within an active space of some orbitals) or semiautomatically (taking all configurations as references that have been shown to be important in a previous CI or MRCI calculation)		Selecting the references can be done manually (<math> \Phi_1, \Phi_2, \Phi_5, ...</math>), automatically (all possible configurations within an active space of some orbitals) or semiautomatically (taking all configurations as references that have been shown to be important in a previous CI or MRCI calculation)

	This method has been implemented first by [[Robert Buenker]] and [[Sigrid D. Peyerimhoff]] in the seventies under the name '''Multi-Reference Single and Double Configuration Interaction''' ('''MRSDCI''').<ref>{{cite journal \|last1=Buenker \|first1=Robert \|last2=Peyerimhoff \|first2=Sigrid D. \|title=Individualized configuration selection in CI calculations with subsequent energy extrapolation \|journal=Theor. Chim. Acta \|date=1974 \|volume=35 \|issue=33\|pages=33–58 \|doi=10.1007/BF02394557 \|s2cid=95594458 }}</ref><ref>{{cite journal \|last1=Buenker \|first1=Robert J. \|last2=Peyerimhoff \|first2=Sigrid D. \|last3=Butscher \|first3=W. \|title=Applicability of the multi-reference double-excitation CI (MRD-CI) method to the calculation of electronic wavefunctions and comparison with related techniques \|journal=Mol. Phys. \|date=1978 \|volume=35\|issue=3 \|pages=771–791 \|doi=10.1080/00268977800100581 }}</ref> MRCI was further streamlined in 1988 by Hans-Joachim Werner and Peter Knowles, which made previous MRCI procedures more generalizable.<ref>{{cite journal \|last1=Werner \|first1=Hans-Joachim \|last2=Knowles \|first2=Peter J. \|title=An efficient internally contracted multiconfiguration–reference configuration interaction method \|journal=Journal of Chemical Physics \|date=17 June 1988 \|volume=89 \|issue=9 \|page=5803 \|doi=10.1063/1.455556 }}</ref>		This method has been implemented first by [[Robert Buenker]] and [[Sigrid D. Peyerimhoff]] in the seventies under the name '''Multi-Reference Single and Double Configuration Interaction''' ('''MRSDCI''').<ref>{{cite journal \|last1=Buenker \|first1=Robert \|last2=Peyerimhoff \|first2=Sigrid D. \|title=Individualized configuration selection in CI calculations with subsequent energy extrapolation \|journal=Theor. Chim. Acta \|date=1974 \|volume=35 \|issue=33\|pages=33–58 \|doi=10.1007/BF02394557 \|s2cid=95594458 }}</ref><ref>{{cite journal \|last1=Buenker \|first1=Robert J. \|last2=Peyerimhoff \|first2=Sigrid D. \|last3=Butscher \|first3=W. \|title=Applicability of the multi-reference double-excitation CI (MRD-CI) method to the calculation of electronic wavefunctions and comparison with related techniques \|journal=Mol. Phys. \|date=1978 \|volume=35\|issue=3 \|pages=771–791 \|doi=10.1080/00268977800100581 \|bibcode=1978MolPh..35..771B }}</ref> MRCI was further streamlined in 1988 by Hans-Joachim Werner and Peter Knowles, which made previous MRCI procedures more generalizable.<ref>{{cite journal \|last1=Werner \|first1=Hans-Joachim \|last2=Knowles \|first2=Peter J. \|title=An efficient internally contracted multiconfiguration–reference configuration interaction method \|journal=Journal of Chemical Physics \|date=17 June 1988 \|volume=89 \|issue=9 \|page=5803 \|doi=10.1063/1.455556 \|bibcode=1988JChPh..89.5803W }}</ref>

	The MRCI method can also be implemented in [[Semi-empirical quantum chemistry method\|semi-empirical]] methods. An example for this is the OM2/MRCI method developed by [[Walter Thiel (Chemist)\|Walter Thiel's]] group.		The MRCI method can also be implemented in [[Semi-empirical quantum chemistry method\|semi-empirical]] methods. An example for this is the OM2/MRCI method developed by [[Walter Thiel (Chemist)\|Walter Thiel's]] group.

Headbomb: ce

2022-10-24T09:45:30Z

← Previous revision		Revision as of 09:45, 24 October 2022
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	Selecting the references can be done manually (<math> \Phi_1, \Phi_2, \Phi_5, ...</math>), automatically (all possible configurations within an active space of some orbitals) or semiautomatically (taking all configurations as references that have been shown to be important in a previous CI or MRCI calculation)		Selecting the references can be done manually (<math> \Phi_1, \Phi_2, \Phi_5, ...</math>), automatically (all possible configurations within an active space of some orbitals) or semiautomatically (taking all configurations as references that have been shown to be important in a previous CI or MRCI calculation)

	This method has been implemented first by [[Robert Buenker]] and [[Sigrid D. Peyerimhoff]] in the seventies under the name '''Multi-Reference Single and Double Configuration Interaction''' ('''MRSDCI''').<ref>{{cite journal \|last1=Buenker \|first1=Robert \|last2=Peyerimhoff \|first2=Sigrid D. \|title=Individualized configuration selection in CI calculations with subsequent energy extrapolation \|journal=Theor. Chim. Acta. \|date=1974 \|volume=35 \|issue=33\|pages=33–58 \|doi=10.1007/BF02394557 \|s2cid=95594458 }}</ref><ref>{{cite journal \|last1=Buenker \|first1=Robert J. \|last2=Peyerimhoff \|first2=Sigrid D. \|last3=Butscher \|first3=W. \|title=Applicability of the multi-reference double-excitation CI (MRD-CI) method to the calculation of electronic wavefunctions and comparison with related techniques \|journal=Mol. Phys. \|date=1978 \|volume=35\|issue=3 \|pages=771–791 \|doi=10.1080/00268977800100581 }}</ref> MRCI was further streamlined in 1988 by Hans-Joachim Werner and Peter Knowles, which made previous MRCI procedures more generalizable.<ref>{{cite journal \|last1=Werner \|first1=Hans-Joachim \|last2=Knowles \|first2=Peter J. \|title=An efficient internally contracted multiconfiguration–reference configuration interaction method \|journal=Journal of Chemical Physics \|date=17 June 1988 \|volume=89 \|issue=9 \|page=5803 \|doi=10.1063/1.455556 }}</ref>		This method has been implemented first by [[Robert Buenker]] and [[Sigrid D. Peyerimhoff]] in the seventies under the name '''Multi-Reference Single and Double Configuration Interaction''' ('''MRSDCI''').<ref>{{cite journal \|last1=Buenker \|first1=Robert \|last2=Peyerimhoff \|first2=Sigrid D. \|title=Individualized configuration selection in CI calculations with subsequent energy extrapolation \|journal=Theor. Chim. Acta \|date=1974 \|volume=35 \|issue=33\|pages=33–58 \|doi=10.1007/BF02394557 \|s2cid=95594458 }}</ref><ref>{{cite journal \|last1=Buenker \|first1=Robert J. \|last2=Peyerimhoff \|first2=Sigrid D. \|last3=Butscher \|first3=W. \|title=Applicability of the multi-reference double-excitation CI (MRD-CI) method to the calculation of electronic wavefunctions and comparison with related techniques \|journal=Mol. Phys. \|date=1978 \|volume=35\|issue=3 \|pages=771–791 \|doi=10.1080/00268977800100581 }}</ref> MRCI was further streamlined in 1988 by Hans-Joachim Werner and Peter Knowles, which made previous MRCI procedures more generalizable.<ref>{{cite journal \|last1=Werner \|first1=Hans-Joachim \|last2=Knowles \|first2=Peter J. \|title=An efficient internally contracted multiconfiguration–reference configuration interaction method \|journal=Journal of Chemical Physics \|date=17 June 1988 \|volume=89 \|issue=9 \|page=5803 \|doi=10.1063/1.455556 }}</ref>

	The MRCI method can also be implemented in [[Semi-empirical quantum chemistry method\|semi-empirical]] methods. An example for this is the OM2/MRCI method developed by [[Walter Thiel (Chemist)\|Walter Thiel's]] group.		The MRCI method can also be implemented in [[Semi-empirical quantum chemistry method\|semi-empirical]] methods. An example for this is the OM2/MRCI method developed by [[Walter Thiel (Chemist)\|Walter Thiel's]] group.

Fadesga: /* References */

2022-07-17T20:14:02Z

References

← Previous revision		Revision as of 20:14, 17 July 2022
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	[[Category:Quantum chemistry]]		[[Category:Quantum chemistry]]
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			{{quantum-chemistry-stub}}

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2022-05-30T03:30:53Z

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← Previous revision		Revision as of 03:30, 30 May 2022
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	Selecting the references can be done manually (<math> \Phi_1, \Phi_2, \Phi_5, ...</math>), automatically (all possible configurations within an active space of some orbitals) or semiautomatically (taking all configurations as references that have been shown to be important in a previous CI or MRCI calculation)		Selecting the references can be done manually (<math> \Phi_1, \Phi_2, \Phi_5, ...</math>), automatically (all possible configurations within an active space of some orbitals) or semiautomatically (taking all configurations as references that have been shown to be important in a previous CI or MRCI calculation)

	This method has been implemented first by [[Robert Buenker]] and [[Sigrid D. Peyerimhoff]] in the seventies under the name '''Multi-Reference Single and Double Configuration Interaction''' ('''MRSDCI''').<ref>{{cite journal \|last1=Buenker \|first1=Robert \|last2=Peyerimhoff \|first2=Sigrid D. \|journal=Theor. Chim. Acta. \|date=1974 \|volume=35 \|issue=33}}</ref><ref>{{cite journal \|last1=Buenker \|first1=Robert J. \|last2=Peyerimhoff \|first2=Sigrid D. \|last3=Butscher \|first3=W. \|journal=Mol. Phys. \|date=1978 \|volume=35}}</ref> MRCI was further streamlined in 1988 by Hans-Joachim Werner and Peter Knowles, which made previous MRCI procedures more generalizable.<ref>{{cite journal \|last1=Werner \|first1=Hans-Joachim \|last2=Knowles \|first2=Peter J. \|title=An efficient internally contracted multiconfiguration–reference configuration interaction method \|journal=Journal of Chemical Physics \|date=17 June 1988 \|volume=89 \|issue=9 \|page=5803 \|doi=10.1063/1.455556 ~~\|access-date=18 May 2022~~}}</ref>		This method has been implemented first by [[Robert Buenker]] and [[Sigrid D. Peyerimhoff]] in the seventies under the name '''Multi-Reference Single and Double Configuration Interaction''' ('''MRSDCI''').<ref>{{cite journal \|last1=Buenker \|first1=Robert \|last2=Peyerimhoff \|first2=Sigrid D. \|title=Individualized configuration selection in CI calculations with subsequent energy extrapolation \|journal=Theor. Chim. Acta. \|date=1974 \|volume=35 \|issue=33\|pages=33–58 \|doi=10.1007/BF02394557 \|s2cid=95594458 }}</ref><ref>{{cite journal \|last1=Buenker \|first1=Robert J. \|last2=Peyerimhoff \|first2=Sigrid D. \|last3=Butscher \|first3=W. \|title=Applicability of the multi-reference double-excitation CI (MRD-CI) method to the calculation of electronic wavefunctions and comparison with related techniques \|journal=Mol. Phys. \|date=1978 \|volume=35\|issue=3 \|pages=771–791 \|doi=10.1080/00268977800100581 }}</ref> MRCI was further streamlined in 1988 by Hans-Joachim Werner and Peter Knowles, which made previous MRCI procedures more generalizable.<ref>{{cite journal \|last1=Werner \|first1=Hans-Joachim \|last2=Knowles \|first2=Peter J. \|title=An efficient internally contracted multiconfiguration–reference configuration interaction method \|journal=Journal of Chemical Physics \|date=17 June 1988 \|volume=89 \|issue=9 \|page=5803 \|doi=10.1063/1.455556 }}</ref>

	The MRCI method can also be implemented in [[Semi-empirical quantum chemistry method\|semi-empirical]] methods. An example for this is the OM2/MRCI method developed by [[Walter Thiel (Chemist)\|Walter Thiel's]] group.		The MRCI method can also be implemented in [[Semi-empirical quantum chemistry method\|semi-empirical]] methods. An example for this is the OM2/MRCI method developed by [[Walter Thiel (Chemist)\|Walter Thiel's]] group.

Trappist the monk: cite repair;

2022-05-19T14:14:41Z

cite repair;

← Previous revision		Revision as of 14:14, 19 May 2022
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	Selecting the references can be done manually (<math> \Phi_1, \Phi_2, \Phi_5, ...</math>), automatically (all possible configurations within an active space of some orbitals) or semiautomatically (taking all configurations as references that have been shown to be important in a previous CI or MRCI calculation)		Selecting the references can be done manually (<math> \Phi_1, \Phi_2, \Phi_5, ...</math>), automatically (all possible configurations within an active space of some orbitals) or semiautomatically (taking all configurations as references that have been shown to be important in a previous CI or MRCI calculation)

	This method has been implemented first by [[Robert Buenker]] and [[Sigrid D. Peyerimhoff]] in the seventies under the name '''Multi-Reference Single and Double Configuration Interaction''' ('''MRSDCI''').<ref>{{cite journal \|last1=Buenker \|first1=Robert \|last2=Peyerimhoff \|first2=Sigrid D. \|journal=Theor. Chim. Acta. \|date=1974 \|volume=35 \|issue=33}}</ref><ref>{{cite journal \|last1=Buenker \|first1=Robert J. \|last2=Peyerimhoff \|first2=Sigrid D. \|last3=Butscher \|first3=W. \|journal=Mol. Phys. \|date=1978 \|volume=35}}</ref> MRCI was further streamlined in 1988 by Hans-Joachim Werner and Peter Knowles, which made previous MRCI procedures more generalizable.<ref>{{cite journal \|last1=Werner \|first1=Hans-Joachim \|last2=Knowles \|first2=Peter J. \|title=An efficient internally contracted multiconfiguration–reference configuration interaction method \|journal=J. ~~Chem.~~ ~~Phys.~~ \|date=17 June 1988 \|volume=89 \|issue=9 \|page=5803 ~~\|pages=12~~ \|doi=~~10.1063/1.455556 \|url=https://aip.scitation.org/doi/~~10.1063/1.455556 \|access-date=18 May 2022}}</ref>		This method has been implemented first by [[Robert Buenker]] and [[Sigrid D. Peyerimhoff]] in the seventies under the name '''Multi-Reference Single and Double Configuration Interaction''' ('''MRSDCI''').<ref>{{cite journal \|last1=Buenker \|first1=Robert \|last2=Peyerimhoff \|first2=Sigrid D. \|journal=Theor. Chim. Acta. \|date=1974 \|volume=35 \|issue=33}}</ref><ref>{{cite journal \|last1=Buenker \|first1=Robert J. \|last2=Peyerimhoff \|first2=Sigrid D. \|last3=Butscher \|first3=W. \|journal=Mol. Phys. \|date=1978 \|volume=35}}</ref> MRCI was further streamlined in 1988 by Hans-Joachim Werner and Peter Knowles, which made previous MRCI procedures more generalizable.<ref>{{cite journal \|last1=Werner \|first1=Hans-Joachim \|last2=Knowles \|first2=Peter J. \|title=An efficient internally contracted multiconfiguration–reference configuration interaction method \|journal=Journal of Chemical Physics \|date=17 June 1988 \|volume=89 \|issue=9 \|page=5803 \|doi=10.1063/1.455556 \|access-date=18 May 2022}}</ref>

	The MRCI method can also be implemented in [[Semi-empirical quantum chemistry method\|semi-empirical]] methods. An example for this is the OM2/MRCI method developed by [[Walter Thiel (Chemist)\|Walter Thiel's]] group.		The MRCI method can also be implemented in [[Semi-empirical quantum chemistry method\|semi-empirical]] methods. An example for this is the OM2/MRCI method developed by [[Walter Thiel (Chemist)\|Walter Thiel's]] group.

GoingBatty: /* top */ fixed reference

2022-05-18T20:00:00Z

top: fixed reference

← Previous revision		Revision as of 20:00, 18 May 2022
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	Selecting the references can be done manually (<math> \Phi_1, \Phi_2, \Phi_5, ...</math>), automatically (all possible configurations within an active space of some orbitals) or semiautomatically (taking all configurations as references that have been shown to be important in a previous CI or MRCI calculation)		Selecting the references can be done manually (<math> \Phi_1, \Phi_2, \Phi_5, ...</math>), automatically (all possible configurations within an active space of some orbitals) or semiautomatically (taking all configurations as references that have been shown to be important in a previous CI or MRCI calculation)

	This method has been implemented first by [[Robert Buenker]] and [[Sigrid D. Peyerimhoff]] in the seventies under the name '''Multi-Reference Single and Double Configuration Interaction''' ('''MRSDCI''').<ref>{{cite journal \|last1=Buenker \|first1=Robert \|last2=Peyerimhoff \|first2=Sigrid D. \|journal=Theor. Chim. Acta. \|date=1974 \|volume=35 \|issue=33}}</ref><ref>{{cite journal \|last1=Buenker \|first1=Robert J. \|last2=Peyerimhoff \|first2=Sigrid D. \|last3=Butscher \|first3=W. \|journal=Mol. Phys. \|date=1978 \|volume=35}}</ref> MRCI was further streamlined in 1988 by Hans-Joachim Werner and Peter Knowles, which made previous MRCI procedures more generalizable.<ref>{{cite journal \|last1=Werner \|first1=Hans-Joachim \|last2=Knowles \|first2=Peter J. \|title=An efficient internally contracted multiconfiguration–reference configuration interaction method \|journal=J. Chem. Phys. \|date=17 June 1988 \|volume=89 \|issue=9 \|page=5803 \|pages=12 \|doi=~~https://doi.org/~~10.1063/1.455556 \|url=https://aip.scitation.org/doi/10.1063/1.455556 \|access-date=18 May 2022}}</ref>		This method has been implemented first by [[Robert Buenker]] and [[Sigrid D. Peyerimhoff]] in the seventies under the name '''Multi-Reference Single and Double Configuration Interaction''' ('''MRSDCI''').<ref>{{cite journal \|last1=Buenker \|first1=Robert \|last2=Peyerimhoff \|first2=Sigrid D. \|journal=Theor. Chim. Acta. \|date=1974 \|volume=35 \|issue=33}}</ref><ref>{{cite journal \|last1=Buenker \|first1=Robert J. \|last2=Peyerimhoff \|first2=Sigrid D. \|last3=Butscher \|first3=W. \|journal=Mol. Phys. \|date=1978 \|volume=35}}</ref> MRCI was further streamlined in 1988 by Hans-Joachim Werner and Peter Knowles, which made previous MRCI procedures more generalizable.<ref>{{cite journal \|last1=Werner \|first1=Hans-Joachim \|last2=Knowles \|first2=Peter J. \|title=An efficient internally contracted multiconfiguration–reference configuration interaction method \|journal=J. Chem. Phys. \|date=17 June 1988 \|volume=89 \|issue=9 \|page=5803 \|pages=12 \|doi=10.1063/1.455556 \|url=https://aip.scitation.org/doi/10.1063/1.455556 \|access-date=18 May 2022}}</ref>

	The MRCI method can also be implemented in [[Semi-empirical quantum chemistry method\|semi-empirical]] methods. An example for this is the OM2/MRCI method developed by [[Walter Thiel (Chemist)\|Walter Thiel's]] group.		The MRCI method can also be implemented in [[Semi-empirical quantum chemistry method\|semi-empirical]] methods. An example for this is the OM2/MRCI method developed by [[Walter Thiel (Chemist)\|Walter Thiel's]] group.

	==See also==		==See also==

GoingBatty: added References section, removed DEFAULTSORT

2022-05-18T19:59:31Z

added References section, removed DEFAULTSORT

← Previous revision		Revision as of 19:59, 18 May 2022
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	* [[Configuration interaction]]		* [[Configuration interaction]]

			==References==
	{{DEFAULTSORT:Multireference Configuration Interaction}}
			{{reflist}}

	[[Category:Quantum chemistry]]		[[Category:Quantum chemistry]]
	<!-- [[Category:Computational chemistry]] redundant -->		<!-- [[Category:Computational chemistry]] redundant -->

130.74.64.119: removed unreferenced status

2022-05-18T17:29:46Z

removed unreferenced status

← Previous revision		Revision as of 17:29, 18 May 2022
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	{{Unreferenced\|date=December 2009}}
	In [[quantum chemistry]], the '''multireference configuration interaction''' (MRCI) method consists of a [[configuration interaction]] expansion of the [[eigenstate]]s of the [[electronic molecular Hamiltonian]] in a set of [[Slater determinant]]s which correspond to excitations of the [[ground state]] [[electronic configuration]] but also of some [[excited state]]s. The Slater determinants from which the excitations are performed are called '''reference determinants'''. The higher excited determinants (also called [[configuration state function]]s (CSFs) or shortly configurations) are then chosen either by the program according to some [[perturbation theory\|perturbation theoretical]] [[ansatz]] according to a threshold provided by the user or simply by truncating excitations from these references to singly, doubly, ... excitations resulting in MRCIS, MRCISD, etc.		In [[quantum chemistry]], the '''multireference configuration interaction''' (MRCI) method consists of a [[configuration interaction]] expansion of the [[eigenstate]]s of the [[electronic molecular Hamiltonian]] in a set of [[Slater determinant]]s which correspond to excitations of the [[ground state]] [[electronic configuration]] but also of some [[excited state]]s. The Slater determinants from which the excitations are performed are called '''reference determinants'''. The higher excited determinants (also called [[configuration state function]]s (CSFs) or shortly configurations) are then chosen either by the program according to some [[perturbation theory\|perturbation theoretical]] [[ansatz]] according to a threshold provided by the user or simply by truncating excitations from these references to singly, doubly, ... excitations resulting in MRCIS, MRCISD, etc.

130.74.64.119: Recent citation-adder here! I'm fixing some mistakes, I noticed upon publication. I'm removing the article links for Knowles and Werner (former links to an athlete, latter has no page - Peter Knowles should absolutely have his own page because he developed Molpro!!). There seems to be some formatting issue with the third source which I'm not sure how to fix - could someone help out?

2022-05-18T17:26:36Z

Recent citation-adder here! I'm fixing some mistakes, I noticed upon publication. I'm removing the article links for Knowles and Werner (former links to an athlete, latter has no page - Peter Knowles should absolutely have his own page because he developed Molpro!!). There seems to be some formatting issue with the third source which I'm not sure how to fix - could someone help out?

← Previous revision		Revision as of 17:26, 18 May 2022
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	Selecting the references can be done manually (<math> \Phi_1, \Phi_2, \Phi_5, ...</math>), automatically (all possible configurations within an active space of some orbitals) or semiautomatically (taking all configurations as references that have been shown to be important in a previous CI or MRCI calculation)		Selecting the references can be done manually (<math> \Phi_1, \Phi_2, \Phi_5, ...</math>), automatically (all possible configurations within an active space of some orbitals) or semiautomatically (taking all configurations as references that have been shown to be important in a previous CI or MRCI calculation)

	This method has been implemented first by [[Robert Buenker]] and [[Sigrid D. Peyerimhoff]] in the seventies under the name '''Multi-Reference Single and Double Configuration Interaction''' ('''MRSDCI''').<ref>{{cite journal \|last1=Buenker \|first1=Robert \|last2=Peyerimhoff \|first2=Sigrid D. \|journal=Theor. Chim. Acta. \|date=1974 \|volume=35 \|issue=33}}</ref><ref>{{cite journal \|last1=Buenker \|first1=Robert J. \|last2=Peyerimhoff \|first2=Sigrid D. \|last3=Butscher \|first3=W. \|journal=Mol. Phys. \|date=1978 \|volume=35}}</ref> MRCI was further streamlined in 1988 by [[Hans-Joachim Werner]] and [[Peter Knowles]], which made previous MRCI procedures more generalizable.<ref>{{cite journal \|last1=Werner \|first1=Hans-Joachim \|last2=Knowles \|first2=Peter J. \|title=An efficient internally contracted multiconfiguration–reference configuration interaction method \|journal=J. Chem. Phys. \|date=17 June 1988 \|volume=89 \|issue=9 \|page=5803 \|pages=12 \|doi=https://doi.org/10.1063/1.455556 \|url=https://aip.scitation.org/doi/10.1063/1.455556 \|access-date=18 May 2022}}</ref>		This method has been implemented first by [[Robert Buenker]] and [[Sigrid D. Peyerimhoff]] in the seventies under the name '''Multi-Reference Single and Double Configuration Interaction''' ('''MRSDCI''').<ref>{{cite journal \|last1=Buenker \|first1=Robert \|last2=Peyerimhoff \|first2=Sigrid D. \|journal=Theor. Chim. Acta. \|date=1974 \|volume=35 \|issue=33}}</ref><ref>{{cite journal \|last1=Buenker \|first1=Robert J. \|last2=Peyerimhoff \|first2=Sigrid D. \|last3=Butscher \|first3=W. \|journal=Mol. Phys. \|date=1978 \|volume=35}}</ref> MRCI was further streamlined in 1988 by Hans-Joachim Werner and Peter Knowles, which made previous MRCI procedures more generalizable.<ref>{{cite journal \|last1=Werner \|first1=Hans-Joachim \|last2=Knowles \|first2=Peter J. \|title=An efficient internally contracted multiconfiguration–reference configuration interaction method \|journal=J. Chem. Phys. \|date=17 June 1988 \|volume=89 \|issue=9 \|page=5803 \|pages=12 \|doi=https://doi.org/10.1063/1.455556 \|url=https://aip.scitation.org/doi/10.1063/1.455556 \|access-date=18 May 2022}}</ref>

	The MRCI method can also be implemented in [[Semi-empirical quantum chemistry method\|semi-empirical]] methods. An example for this is the OM2/MRCI method developed by [[Walter Thiel (Chemist)\|Walter Thiel's]] group.		The MRCI method can also be implemented in [[Semi-empirical quantum chemistry method\|semi-empirical]] methods. An example for this is the OM2/MRCI method developed by [[Walter Thiel (Chemist)\|Walter Thiel's]] group.