The Unitary Group Adapted State-Specific Multi-Reference Perturbation Theory (UGA-SSMRPT2) developed by Mukherjee et al. [J. Comput. Chem. 36, 670 (2015)] has successfully realized the goal of studying bond dissociation in a numerically stable, spin-preserving, and size-consistent manner. We explore and analyze here the efficacy of the UGA-SSMRPT2 theory in the description of the avoided crossings and interlacings between a manifold of potential energy curves for states belonging to the same space-spin symmetry. Three different aspects of UGA-SSMRPT2 have been studied: (a) We introduce and develop the most rigorous version of UGA-SSMRPT2 that emerges from the rigorous version of UGA-SSMRCC utilizing a linearly independent virtual manifold; we call this the “projection” version of UGA-SSMRPT2 (UGA-SSMRPT2 scheme P). We compare and contrast this approach with our earlier formulation that used extra sufficiency conditions via amplitude equations (UGA-SSMRPT2 scheme A). (b) We present the results for a variety of electronic states of a set of molecules, which display the striking accuracy of both the two versions of UGA-SSMRPT2 with respect to three different situations involving weakly avoided crossings, moderate/strongly avoided crossings, and interlacing in a manifold of potential energy curves (PECs) of the same symmetry. Accuracy of our results has been benchmarked against IC-MRCISD + Q. (c) For weakly avoided crossing between states displaying differently charged sectors around the crossing region, the insufficient inclusion of state-specific orbital relaxation and the absence of dynamic correlation induced by orbital relaxation in the first order wavefunction for a second order perturbative theory lead to an artifact of double crossing between the pair of PECs.
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7 July 2021
Research Article|
July 01 2021
Exploration of interlacing and avoided crossings in a manifold of potential energy curves by a unitary group adapted state specific multi-reference perturbation theory (UGA-SSMRPT) Available to Purchase
Dibyajyoti Chakravarti
;
Dibyajyoti Chakravarti
a)
1
School of Chemical Sciences, Indian Association for the Cultivation of Science
, Kolkata, India
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Koustav Hazra;
Koustav Hazra
1
School of Chemical Sciences, Indian Association for the Cultivation of Science
, Kolkata, India
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Riya Kayal;
Riya Kayal
1
School of Chemical Sciences, Indian Association for the Cultivation of Science
, Kolkata, India
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Sudip Sasmal
;
Sudip Sasmal
b)
2
Physikalisch-Chemisches Institut, Universität Heidelberg
, Heidelberg, Germany
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Debashis Mukherjee
Debashis Mukherjee
c)
3
Centre for Quantum Engineering, Research, and Education (CQuERE), TCG-CREST
, Kolkata, India
c)Author to whom correspondence should be addressed: [email protected]
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Dibyajyoti Chakravarti
1,a)
Koustav Hazra
1
Riya Kayal
1
Sudip Sasmal
2,b)
Debashis Mukherjee
3,c)
1
School of Chemical Sciences, Indian Association for the Cultivation of Science
, Kolkata, India
2
Physikalisch-Chemisches Institut, Universität Heidelberg
, Heidelberg, Germany
3
Centre for Quantum Engineering, Research, and Education (CQuERE), TCG-CREST
, Kolkata, India
a)
Electronic mail: [email protected]
b)
Electronic mail: [email protected]
c)Author to whom correspondence should be addressed: [email protected]
J. Chem. Phys. 155, 014101 (2021)
Article history
Received:
April 21 2021
Accepted:
June 14 2021
Citation
Dibyajyoti Chakravarti, Koustav Hazra, Riya Kayal, Sudip Sasmal, Debashis Mukherjee; Exploration of interlacing and avoided crossings in a manifold of potential energy curves by a unitary group adapted state specific multi-reference perturbation theory (UGA-SSMRPT). J. Chem. Phys. 7 July 2021; 155 (1): 014101. https://doi.org/10.1063/5.0054731
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