An ab initio study of tunneling splittings in the water dimer

Tunneling splittings in the water dimer have been determined by the semiclassical WKB method, based on pathways characterized at the computational level of second-order M?ller-Plesset (MP2) theory with basis sets of aug-cc-pVTZ quality. This calculation takes into account all three acceptor tunneling, donor-acceptor interchange, and bifurcation tunneling rearrangements of the water dimer. The tunneling splittings were evaluated as 7.73 cm(-1) (large splitting) and 0.42 cm(-1) (small splitting), which are in good agreement with the corresponding experimental values of 11.18 cm(-1) and 0.70 cm(-1), respectively.