  A first-order liquid-liquid phase transition in high-pressure hydrogen
between molecular and atomic fluid phases has been predicted in computer
simulations using ab initio molecular dynamics approaches. However, experiments
indicate that molecular dissociation may occur through a continuous crossover
rather than a first-order transition. Here we study the nature of molecular
dissociation in fluid hydrogen using an alternative simulation technique in
which electronic correlation is computed within quantum Monte Carlo, the
so-called Coupled Electron Ion Monte Carlo (CEIMC) method. We find no evidence
for a first-order liquid-liquid phase transition.
