Treatment of rigid bodies by diffusion Monte Carlo: Application to the para-H2⋅⋅⋅H2O and ortho-H2⋅⋅⋅H2O clusters

Application of the diffusion Monte Carlo method is discussed for ground states of molecular systems in which molecules are treated as rigid bodies. The method is applied to the investigation of the para-H2...H2O and ortho-H2...H2O clusters. Significant differences are demonstrated in the bonding of para-H2 and ortho-H2 to the water molecule.