Nonadiabatic Potential Energy Surfaces for a Molecule on a Surface as Found by Constrained Complete Active Space Theory

Inorder to study electron-transfer mediated chemical processeson a metal surface, one requires not one but two potential energysurfaces (one ground state and one excited state) as in Marcus theory.In this letter, we report that a novel, dynamically weighted, state-averagedconstrained CASSCF(2,2) (DW-SA-cCASSCF(2,2)) can produce such surfacesfor the Anderson impurity model. Both ground and excited state potentialsare smooth, they incorporate states with a charge transfer character,and the accuracy of the ground state surface can be verified for somemodel problems by renormalization group theory. Future developmentof gradients and nonadiabatic derivative couplings should allow forthe study of nonadiabatic dynamics for molecules near metal surfaces.