BASIS-SET AND NUCLEAR-RELAXATION EFFECTS IN HOLE AND ELECTRON-TRANSFER IN A WATER DIMER SYSTEM

Electronic coupling elements between initial and final-states for a mo del water dimer system were calculated for hole and electron transfer reactions using the corresponding orbitals method of King, With an ext ension to allow for differing initial- and final-state nuclear geometr ies, Three basis sets, 6-311G, 6-311 + + G and 6-311 + + G(3pd, 3df), were used, and calculations were performed approximating slow (nuclear relaxation included) or fast (no nuclear relaxation) timescales. Elec tronic overlaps and coupling elements were observed to decay exponenti ally and smoothly with separation in the case of hole transfer in all combinations of slow vs. fast and basis sets. In the case of electron transfer, the decay of coupling was strongly basis set dependent, givi ng rapid and unrealistic decay at short distances with the non-diffuse -extended basis set, and approximately exponential decay with diffuse- extended basis sets. The addition of diffuse functions to the 6-311 G basis set is significant and important in these calculations, while th e addition of polarization functions seems to have little importance.