Construction scheme for regularized diabatic states

Abstract

A simple construction scheme for quasidiabatic electronic states implemented earlier for a Jahn–Teller situation [J. Chem. Phys. 110, 9371 (1999)] is extended to the case of a seam of symmetry-allowed conical intersections. It is based on the idea of removing only the singular part of the nonadiabatic coupling elements, leading to the notion of “regularized” diabatic states. Explicit working equations are given for the resulting potential energy matrix which require only information from the adiabatic potential energy surfaces alone. The approach is tested for the photodissociation of H2S and O3 and very good agreement with reference data from the literature is found.

HN2(2A‘) Electronic Manifold. II. Ab Initio Based Double-Sheeted DMBE Potential Energy Surface via a Global Diabatization Angle

“…Such a warranty is not insured by direct diabatization schemes either providing diabatic wave functions 26,47-51 or diabatic energies. 62,63 The method can be classified as an indirect diabatization procedure that allows a well-defined global zeroth-order solution. In fact, it provides a diabatic grid of points with a proper description of the crossing seams in their full dimensionality, which is key for the study of nonadiabatic processes.…”

“…Also for H 2 S, Köppel et al 62 have implemented the diabatization procedure of Thiel and Köppel,28 where the main idea is to remove only the part responsible for the singularities from the nonadiabatic coupling term via a unitary transformation. Their results were compared with those of Simah et al, 49 showing that their diabats do not merge either the adiabats at the HS-S dissociation channel.…”

Introductory lecture: Nonadiabatic effects in chemical dynamics

“…(Such a transformation has also been used fruitfully by other workers, based on other criteria. 37,42 ) In order for this to produce useful diabatic states, it is necessary to first re-express the configuration state functions (CSFs) in terms of diabatic molecular orbitals (DMOs), and these are produced by the fourfold way. The essential step in using the fourfold way to obtain DMOs is maximizing a three-parameter functional that involves the sum of the squares of the orbital occupation numbers for all of the states, a state-averaged natural orbital term, 38 and a transition density term.…”

The Diabatic Picture of Electron Transfer, Reaction Barriers, and Molecular Dynamics

“…It can be shown that this procedure minimizes the 2 norm of the derivative coupling (|d| 2 = min) in the vicinity of the reference point [30]. Other techniques in the same spirit include: enforcing configurational uniformity, so that each diabatic wavefunction is predominantly constructed from a fixed set of electronic configurations [31,32]; regularizing adiabatic states to remove the divergent portion of the coupling [33,34]; and the fourfold way, which combines many of the positive features of the above methods [35,36]. As a starting point, these techniques require a very accurate description adiabatic states and are thus typically used in conjunction with high-level CI calculations.…”