Excited state structures and vibronic spectra of H2CO+, HDCO+, and D2CO+ using molecular gradient and Hessian techniques

Abstract

We choose H2CO+ and its deuterated species to demonstrate the potential for using second-order multiconfigurational self-consistent field theory to optimize structures and calculate properties of ionized and excited states. We focus on the calculation of multidimensional vibronic spectra using only the local information of the potential hypersurface, viz. the molecular energy, gradient, and Hessian. Second-order multiconfigurational self-consistent field optimization on lowest excited states using the trust radius algorithm is found to give the same stable convergence as for neutral ground states, while for higher lying states, the problem of multidimensional potential crossings renders the calculations more difficult.