CALCULATIONS OF THE TUNNELING SPLITTINGS IN WATER DIMER AND TRIMER USING DIFFUSION MONTE-CARLO

The diffusion Monte Carlo (DMC) method is used to calculate rovibrational bound states of the water dimer and trimer. The rigid body form of DMC is employed, together with correlated sampling of energy differences between states of different symmetry. This allows calculation of the tunneling splittings in (H2O)2 and (H2O)3. The results for (H2O)2 are in quite good agreement with those obtained using a basis set method, and also agree well with experiment. In addition, we have made predictions for similar splittings in (D2O)3 and several water dimer isotopomers. In all the calculations, we have used the potential energy surface due to Millot and Stone which is known to give quite good agreement with experiment for the tunneling splittings in (H 2O)2. © 1995 American Institute of Physics.