title: Second-order many-body perturbation and coupled-cluster singles and doubles study of ice VIII.
abstract: The structure, equation of state, IR, Raman, and inelastic neutron scattering (INS) spectra of high-pressure, proton-ordered phase VIII of ice are calculated by the second-order many-body perturbation and coupled-cluster singles and doubles methods. Nearly all the observed features of the pressure-dependence of the structures and spectra are reproduced computationally up to 60 GPa insofar as the anharmonic effects can be neglected. The calculations display no sign of the hypothetical isostructural transition in 2-3 GPa to phase VIII('), the existence of which has been a matter of controversy for over a decade, while they do not contradict the interpretation of the spectral anomaly at 10-14 GPa as a precursor of the VIII-X phase transition. The calculated INS spectra correct a systematic error in the peak positions of the observed spectra.
authors.affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.
authors.forename: Kandis
authors.initials: K
authors.lastname: Gilliard
authors.affiliation: Department of Chemistry, University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, USA.
authors.forename: Olaseni
authors.initials: O
authors.lastname: Sode
authors.affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.
authors.forename: So
authors.initials: S
authors.lastname: Hirata