Quantum chemical studies on hydrogen bonded systems. Need for large scale computations

The sequential and parallel proton transfer mechanism has been considered for some model hydrogen bonded systems. The results of preliminary quantum chemical calculations distinctly show that the proton displacement within hydrogen bridges appears to be a coupled process. Furthermore, in order to come to a better understanding of the proton transfer phenomena the authors must look at the system with its ion and solvent environment. In quantum chemical calculations at the Hartree-Fock level performed for model hydrogen bonded systems the effect of the basis set has been emphasized. Except of basis saturation, the role of polarization functions on the hydrogen bond proton seems to be of essential importance leading to the substantial enhancing of the potential barrier for the proton transfer. On the other hand, the role of correlation cannot be neglected as well giving rise to an essential lowering of the barrier. The results of recent quantum chemical studies clearly show that only large scale computations enable reliable conclusions on the proton transfer mechanism