Path integral molecular dynamics calculations of the and clusters on an ab initio potential energy surface

Path integral molecular dynamics simulations for the H 6 + and D 6 + cluster cations have been carried out in order to understand the floppy nature of their molecular structure due to quantum-mechanical fluctuation. A full-dimensional analytical potential energy surface for the ground electronic state of H 6 + has been developed on the basis of accurate ab initio electronic structure calculations at the CCSD(T)/cc-pVTZ level. It is found that the outer H2(D2) nuclei rotate almost freely and that the probability density distributions of the central H2(D2) nuclei show strong spatial delocalization.