Nonadiabatic potential-energy surfaces by constrained density-functional theory

Nonadiabatic effects play an important role in many chemical processes. In order to study the underlying nonadiabatic potential-energy surfaces (PESs), we present a locally constrained density-functional theory approach, which enables us to confine electrons to subspaces of the Hilbert space, e.g., to selected atoms or groups of atoms. This allows one to calculate nonadiabatic PESs for defined charge and spin states of the chosen subsystems. The capability of the method is demonstrated by calculating nonadiabatic PESs for the scattering of a sodium and a chlorine atom, for the interaction of a chlorine molecule with a small metal cluster, and for the dissociation of an oxygen molecule at the Al(111) surface.