We have employed extended multiconfiguration quasidegenerate perturbation theory, fourfold-way diabatic molecular orbitals, and configurational uniformity to develop a global three-state diabatic representation of the potential energy surfaces and their couplings for the electronically nonadiabatic reaction OH* + H2 → H2O + H, where * denotes electronic excitation to the A 2ς+ state. To achieve sign consistency of the computed diabatic couplings, we developed a graphics processing unit-accelerated algorithm called the cluster-growing algorithm. Having obtained consistent signs of the diabatic couplings, we fit the diabatic matrix elements (which consist of the diabatic potentials and the diabatic couplings) to analytic representations. Adiabatic potential energy surfaces are generated by diagonalizing the 3 × 3 diabatic potential energy matrix. The comparisons between the fitted and computed diabatic matrix elements and between the originally computed adiabatic potential energy surfaces and those generated from the fits indicate that the current fit is accurate enough for dynamical studies, and it may be used for quantal or semiclassical dynamics calculations.
Bibliographical noteFunding Information:
This work was supported in part by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award No. DE-SC0015997. A.G.S.de O.-F. acknowledges support from the CoordenaÃ§Ã£o de AperfeiÃ§oamento de Pessoal de NÃ-vel Superior-Brasil (CAPES)-Finance Code 001 and the Conselho Nacional de Desenvolvimento CientÃ-fico e TecnolÃgico (CNPq) under Grant Nos. 306830/2018-3 and 421077/2018-2.
© 2019 Author(s).