Abstract
Unitary parametrization of the wave operator in the form suggested by Mayer is studied in the multireference framework. The investigated unitary perturbation theory (UPT) constructs a first correction in terms of the functions having nonzero interaction with the reference state via the Hamiltonian. Parameters in the exponential of the wave operator are determined by two dimensional eigenvalue equations. Because of the unitary mapping, UPT is unaffected by the quasi-degeneracy problem, making it an ideal tool for correcting multireference starting functions. Lack of size-consistency is however a shortcoming of the method. Applications of UPT as well as the related degeneracy-corrected PT (DCPT) are presented on intruder prone examples like the symmetric dissociation of the water molecule, the BeH2 system and the two lowest lying states of the scandium dimer. Size consistency violation is analysed and evaluated on the example of the water dimer. Tractability of excited states by UPT is examined by computing the singlet-triplet splitting of the CH2 molecule.
| Original language | English |
|---|---|
| Pages (from-to) | 230-238 |
| Number of pages | 9 |
| Journal | International Journal of Quantum Chemistry |
| Volume | 113 |
| Issue number | 3 |
| DOIs | |
| Publication status | Published - Feb 5 2013 |
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Keywords
- intruder state problem
- Jacobi rotation
- multireference function
- perturbation theory
- unitary wave operator
ASJC Scopus subject areas
- Condensed Matter Physics
- Atomic and Molecular Physics, and Optics
- Physical and Theoretical Chemistry
Cite this
Unitary perturbation theory applied to multiconfigurational reference functions. / Nagy, Péter R.; Szabados, A.
In: International Journal of Quantum Chemistry, Vol. 113, No. 3, 05.02.2013, p. 230-238.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Unitary perturbation theory applied to multiconfigurational reference functions
AU - Nagy, Péter R.
AU - Szabados, A.
PY - 2013/2/5
Y1 - 2013/2/5
N2 - Unitary parametrization of the wave operator in the form suggested by Mayer is studied in the multireference framework. The investigated unitary perturbation theory (UPT) constructs a first correction in terms of the functions having nonzero interaction with the reference state via the Hamiltonian. Parameters in the exponential of the wave operator are determined by two dimensional eigenvalue equations. Because of the unitary mapping, UPT is unaffected by the quasi-degeneracy problem, making it an ideal tool for correcting multireference starting functions. Lack of size-consistency is however a shortcoming of the method. Applications of UPT as well as the related degeneracy-corrected PT (DCPT) are presented on intruder prone examples like the symmetric dissociation of the water molecule, the BeH2 system and the two lowest lying states of the scandium dimer. Size consistency violation is analysed and evaluated on the example of the water dimer. Tractability of excited states by UPT is examined by computing the singlet-triplet splitting of the CH2 molecule.
AB - Unitary parametrization of the wave operator in the form suggested by Mayer is studied in the multireference framework. The investigated unitary perturbation theory (UPT) constructs a first correction in terms of the functions having nonzero interaction with the reference state via the Hamiltonian. Parameters in the exponential of the wave operator are determined by two dimensional eigenvalue equations. Because of the unitary mapping, UPT is unaffected by the quasi-degeneracy problem, making it an ideal tool for correcting multireference starting functions. Lack of size-consistency is however a shortcoming of the method. Applications of UPT as well as the related degeneracy-corrected PT (DCPT) are presented on intruder prone examples like the symmetric dissociation of the water molecule, the BeH2 system and the two lowest lying states of the scandium dimer. Size consistency violation is analysed and evaluated on the example of the water dimer. Tractability of excited states by UPT is examined by computing the singlet-triplet splitting of the CH2 molecule.
KW - intruder state problem
KW - Jacobi rotation
KW - multireference function
KW - perturbation theory
KW - unitary wave operator
UR - http://www.scopus.com/inward/record.url?scp=84872976319&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84872976319&partnerID=8YFLogxK
U2 - 10.1002/qua.24103
DO - 10.1002/qua.24103
M3 - Article
VL - 113
SP - 230
EP - 238
JO - International Journal of Quantum Chemistry
JF - International Journal of Quantum Chemistry
SN - 0020-7608
IS - 3
ER -