Explication and revision of generalized Van Vleck perturbation theory for molecular electronic structure

Abstract

The electronic structure of the triiodide ion from relativistic correlated calculations: A comparison of different methodologies J. Chem. Phys. 133, 064305 (2010); 10.1063/1.3474571 Relativistic quasidegenerate perturbation theory with four-component general multiconfiguration reference functionsThe 1 2 A 1 , 1 2 B 2 , and 1 2 A 2 states of the SO 2 + ion studied using multiconfiguration second-order perturbation theory Generalized molecular mechanics including quantum electronic structure variation of polar solvents. I. Theoretical formulation via a truncated adiabatic basis set description

Molecular electric dipole moments using the GVVPT2 variant of multireference perturbation theory

“…Since the GVVPT2 method [3] and its high performance implementation [17] have been described in previous publications, here only salient features critical to the evaluation of the electric dipole are reviewed. In GVVPT2, the configuration space, in which the N Plowest electronic states are sought, is divided into two subspaces: a model MCSCF subspace, L M (dim L M > N P ), specified by a given set of reference electron configurations, and an external subspace, L Q , whose configurations are related to the reference ones through single and double excitations (N.B.…”

“…The problem of energy derivatives in a multi-root effective Hamiltonian using a Lagrangian formulation was first addressed in the context of multi-root coupled cluster [7][8][9][10]. Since GVVPT2 uses both variational and nonvariational internal parameters [3], there is need to consider the nonvariational parameters in a manner that avoids calculating nth order responses for nth order properties. The Lagrangian approach allows one to reformulate the task in such a way that all internal parameters of the method can be considered as variational for a modified energy Lagrangian with undefined multipliers, which simplifies essentially the task of analytical evaluation of the GVVPT2 energy derivatives.…”

“…Generalized Van Vleck Perturbation Theory (GVVPT) [1][2][3] is a subspace-specific variant of multireference (or quasidegenerate) perturbation theory that, in contrast to most computationally feasible MRPTs or QDPTs, accounts for the interaction of the perturbed model space functions (e.g., MCSCF states) of interest with the unperturbed complementary states. Perhaps most importantly, GVVPT avoids completely the notorious 'intruder state' problem, even when considering excited electronic states.…”

Full configuration interaction calculation of BeH adiabatic states

“…Most of these methods face the difficulties by means of multireference ͑MR͒ approaches ͓e.g., multireference configuration interaction ͑CI͒ more or less corrected for sizeconsistency error effects [5][6][7][8][9][10][11] or multireference perturbation theory [12][13][14][15] ͔. The extension of the single-reference configurations interaction ͑SR-CI͒ to the MR case is conceptually straightforward.…”

Pyrazine excited states revisited using the extended multi-state complete active space second-order perturbation method

“…There are also similar approaches called generalized Van-Vleck perturbation theories. 22,23 Although MS-CASPT2 improves the description of electronic structures around conical intersections and avoided crossings in comparison to the single state CASPT2, there are still many cases where MS-CASPT2 PESs become singular at crossing points. 24 A remedy has been first proposed by Granovsky,25 who has proposed the 'extended' MCQDPT method, which is a generalization of the uncontracted MCQDPT of Nakano.…”