  Effects of pressure and temperature on structural and thermodynamic
properties of ice VII have been studied by using path-integral molecular
dynamics (PIMD) simulations. Temperatures between 25 and 450 K, as well as
pressures up to 12 GPa were considered. Interatomic interactions were modeled
by using the effective q-TIP4P/F potential for flexible water. We analyze the
pressure dependence of the molar volume, bulk modulus, interatomic distances,
kinetic energy, and atomic delocalization at various temperatures. Results of
PIMD simulations are compared with those derived from a quasi-harmonic
approximation (QHA) of vibrational modes, which helps to assess the importance
of anharmonic effects, as well as the influence of the different modes on the
properties of ice VII. The accuracy of the QHA for describing this
high-pressure phase decreases for rising temperature, but this approximation
becomes more reliable as pressure grows, since anharmonicity becomes less
relevant. Comparisons with low-pressure cubic ice are presented.
