Critical point particle number fluctuations from molecular dynamics

Particle number fluctuations are studied in a vicinity of the critical point and inside the mixed phase for a system with the liquid-gas 1st order phase transition. We use molecular dynamics simulations of the classical Lennard-Jones fluid in a periodic box. The numerical solution of the problem incorporates all correlations, exact conservation laws, and finite size effects, allowing us to study the fluctuation signatures of the critical point in a dynamical setup. We find that large fluctuations associated with the critical point and inside the mixed phase are observed when measurements are performed in coordinate subspace, but, in the absence of collective flow and expansion, are essentially washed out when momentum cuts are imposed instead.