Analytic non-adiabatic derivative coupling terms for spin-orbit MRCI wavefunctions. II. Derivative coupling terms and coupling angle for KHeA2Π1/2⇔KHeB2Σ1/2

Abstract

A method for calculating the analytic nonadiabatic derivative coupling terms (DCTs) for spin-orbit multi-reference configuration interaction wavefunctions is reviewed. The results of a sample calculation using a Stuttgart basis for KHe are presented. Additionally, the DCTs are compared with a simple calculation based on the Nikitin’s 3 × 3 description of the coupling between the Σ and Π surfaces, as well as a method based on Werner’s analysis of configuration interaction coefficients. The nonadiabatic coupling angle calculated by integrating the radial analytic DCTs using these different techniques matches extremely well. The resultant nonadiabatic energy surfaces for KHe are presented.

Electronic Structure Methods for the Description of Nonadiabatic Effects and Conical Intersections

“…127,128,132,385 The NAC in COLUMBUS has also been expanded recently to the relativistic MRCI-SD method. 386,387 MRCISD NAC has also been developed by Hoffmann and coworkers extending to state-averaged MCSCF where the states do not need to have the same weights. 388 Implementations of CASSCF NAC are the most widespread and exist in most packages with MCSCF capabilities, such as COLUMBUS, 132 GAMESS, 187,188 GAUSSIAN, 389 MOLPRO, 176 MOL-CAS, 175 and OPENMOLCAS.…”

“…Implementations of analytic gradients and derivative couplings at the MRCI level are not as widespread as CASSCF ones. The Columbus software is a main publicly distributed software that has analytic gradients readily available and extended them to NAC. ,,, The NAC in Columbus has also been expanded recently to the relativistic MRCI-SD method. , MRCISD NAC has also been developed by Hoffmann and co-workers extending to state-averaged MCSCF where the states do not need to have the same weights …”

Ab initio molecular dynamics study of intersystem crossing dynamics for MH2 (M = Si, Ge, Sn, Pb) on spin‐pure and spin‐mixed potential energy surfaces

“…To perform such SH-AIMD simulations based on spin-mixed states, the SOC must be taken into account for the potential gradient and the NAC. Unfortunately, there are only a few methods and programs that can analytically calculate the gradient and NAC terms of the spin-mixed states, [24][25][26] and their application to ISC dynamics has not yet progressed. As one solution, Kamiya et al 27 developed a TFS-SH-AIMD code utilizing numerically evaluated gradients and NAC terms of the spin-mixed states and applied it to the photodissociation reaction of methyl iodide.…”