Knowledge Bank

Diffusion Monte Carlo (DMC) has been shown to be a successful technique for treating the quantum zero-point effects of floppy molecules and clusters. Here, we report the results of our fixed-node DMC methodology when applied to the model systems H3+ and H2D+. The fixed-node approach has been developed to account for the nodes in the wave functions of rotationally excited states. The accuracy of our fixed-node DMC studies will be examined and compared with other methods. In particular, a comparison with converged variational calculations provides the most thorough test of the effectiveness of our methodology over a large range of quantum states. The fixed-node DMC methodology produces more accurate energetic calculations than evaluations using a rigid rotor model of the excited states of fluxional molecules.