  We report an exhaustive numerical study of the statistical properties of the
potential energy landscape of TIP4P/2005, one of the most accurate rigid water
models. We show that, in the region where equilibrated configurations can be
generated, a Gaussian landscape description is able to properly describe the
model properties. We also find that the volume dependence of the landscape
properties is consistent with the existence of a locus of density maxima in the
phase diagram. The landscape-based equation of state accurately reproduces the
TIP4P/2005 pressure-vs-volume curves, providing a sound extrapolation of the
free-energy at low T. A positive-pressure liquid-liquid critical point is
predicted by the resulting free-energy.
