Density - Functional Study of theHydrogen - Bonded Water Cluster H 5 O + 2

We study the H 5 O + 2 molecule as a basic unit of the proton transfer in hydrogen-bonded water networks in density-functional theory (DFT) scheme using the nite-diierence pseudopotential method. The comparison of dissociation energies obtained from the local-density approximation (LDA) and the generalized-gradient approximation (GGA) with experimental results and other accurate quantum chemistry calculations shows that (1) the GGA in DFT is a reliable scheme for this system, and (2) we can obtain the eeect of including higher correlation by using the GGA over the LDA. We also address the technical issue of implementing the GGA exchange-correlation potential in the real space. The transport of protons plays an important role in life processes. Proton transfers , for example, are central in the Peter Mitchell's now well-accepted hypothesis of biological energy transductions 1]. In his chemiosmotic theory, which explains how adenosine diphosphate (ADP) get converted back into the high energy form of adenosine triphosphate (ATP), the existence of proton pumps is crucial. The work by Caeri and his colleagues has also shown that the proton conductivity is an important feature of the bio-process 2]: Measuring the conductivity of nearly dry biological samples as the moisture content of normal and heavy water was increased , they have shown that the conductivity is mainly protonic and further the protonic conductivity coincides with the onset of biological activity. However important it is, the detailed understanding of the proton transfer mechanism is still lacking, and this is mainly due to the lack of our understanding of the interaction between biological molecules and water and between water molecules themselves. One important clue to this question should be the fact that protons are dominant charge carriers in hydrogen-bonded materials and that they move 1)