Vibrational excited states by diffusion Monte Carlo

Methods for evaluating vibrationally excited states by DMC within the fixed-node approximation are described. Two central issues are identified. The first, and most important, is the identification of the coordinates that will be used to describe the molecular vibrations. The second is the determination of where the node should be placed. Strategies for addressing both of these issues are discussed within the context of the fundamental vibrations in Ne 2 OH and H 3 O 2 - .