  We perform successive umbrella sampling grand canonical Monte Carlo computer
simulations of the original ST2 model of water in the vicinity of the proposed
liquid-liquid critical point, at temperatures above and below the critical
temperature. Our results support the previous work of Y. Liu, A.Z.
Panagiotopoulos and P.G. Debenedetti [J. Chem. Phys. {\bf 131}, 104508 (2009)],
who provided evidence for the existence and location of the critical point for
ST2 using the Ewald method to evaluate the long-range forces. Our results
therefore demonstrate the robustness of the evidence for critical behavior with
respect to the treatment of the electrostatic interactions. In addition, we
verify that the liquid is equilibrated at all densities on the Monte Carlo time
scale of our simulations, and also that there is no indication of crystal
formation during our runs. These findings demonstrate that the processes of
liquid-state relaxation and crystal nucleation are well separated in time.
Therefore, the bimodal shape of the density of states, and hence the critical
point itself, is a purely liquid-state phenomenon that is distinct from the
crystal-liquid transition.
