摘要：

We report diffusion quantum Monte Carlo (DMC) calculations of the equilibrium dissociation energyDeof the water dimer. The dissociation energy measured experimentally,D0, can be estimated fromDeby adding a correction for vibrational effects. Using the measured dissociation energy and the modern value of the vibrational energyMaset al., [J. Chem. Phys.113,6687(2000)]leads toDe=5.00±0.7kcalmol−1, although the resultCurtisset al., [J. Chem. Phys.71,2703(1979)]De=5.44±0.7kcalmol−1, which uses an earlier estimate of the vibrational energy, has been widely quoted. High-level coupled cluster calculationsKlopperet al., [Phys. Chem. Chem. Phys.2,2227(2000)]have yieldedDe=5.02±0.05kcalmol−1. In an attempt to shed new light on this old problem, we have performed all-electron DMC calculations on the water monomer and dimer using Slater-Jastrow wave functions with both Hartree-Fock approximation (HF) and B3LYP density functional theory single-particle orbitals. We obtain equilibrium dissociation energies for the dimer of5.02±0.18kcalmol−1(HF orbitals) and5.21±0.18kcalmol−1(B3LYP orbitals), in good agreement with the coupled cluster results.

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