Ab initio study of nonadiabatic coupling matrix elements between excited [formula omitted] and [formula omitted] electronic states of C 2H

Abstract

The conical intersection (CI) between the 2 2 A ′ and 3 2 A ′ electronic states of C 2H occurring at the C 2v-symmetric geometry has been characterized by line integral calculations using ab initio nonadiabatic matrix coupling elements. The calculations confirmed that when a path surrounds this CI and does not approach, too closely, CIs formed by adjacent states, the line integral produces for the topological phase, the expected π-value. Increasing the radius of the circle was accompanied by a decrease in the topological phase indicating on the existence of other CIs in the vicinity of the present one.