Full-dimensional quantum calculations of the dissociation energy, zero-point, and 10 K properties of H7+/D7+ clusters using an ab initio potential energy surface

Diffusion Monte Carlo (DMC) and path-integral Monte Carlo computations of the vibrational ground state and 10 K equilibrium state properties of the H-7(+)/D-7(+) cations are presented, using an ab initio full-dimensional potential energy surface. The DMC zero-point energies of dissociated fragments H-5(+)(D-5(+))+H-2(D-2) are also calculated and from these results and the electronic dissociation energy, dissociation energies, D-0, of 752 +/- 15 and 980 +/- 14 cm(-1) are reported for H-7(+) and D-7(+), respectively. Due to the known error in the electronic dissociation energy of the potential surface, these quantities are underestimated by roughly 65 cm(-1). These values are rigorously determined for first time, and compared with previous theoretical estimates from electronic structure calculations using standard harmonic analysis, and available experimental measurements. Probability density distributions are also computed for the ground vibrational and 10 K state of H-7(+) and D-7(+). These are qualitatively described as a central H-3(+)/D-3(+) core surrounded by "solvent" H-2/D-2 molecules that nearly freely rotate. (C) 2013 AIP Publishing LLC.