  Using first-principles molecular dynamics, we study the influence of nuclear
quantum effects (NQEs) and nonlocal exchange--correlation density functionals
(DFs) near molecular dissociation in liquid hydrogen. NQEs strongly influence
intramolecular properties, such as bond stability, and are thus an essential
part of the dissociation process. Moreover, by including DFs that account for
either the self-interaction error or dispersion interactions, we find a much
better description of molecular dissociation and metallization than previous
studies based on classical protons and/or local or semi-local DFs. We obtain
excellent agreement with experimentally measured optical properties along
pre-compressed Hugoniots, and while we still find a first-order liquid--liquid
transition at low temperatures, transition pressures are increased by more than
100 GPa.
