[N]pT ensemble and finite-size scaling study of the GEM-4 critical isostructural transition

First-order transitions of system where both lattice site occupancy and lattice spacing fluctuate, such as cluster crystals, cannot be efficiently studied by traditional simulation methods. These methods necessarily fix one of these two degrees of freedom, but this difficulty is surmounted by the generalized [N]pT ensemble [J. Chem. Phys. 136, 214106 (2012)]. Here it is shown that histogram reweighting and the [N]pT ensemble can be used to study an isostructural transition between cluster crystals of different occupancy in the generalized exponential model of index 4 (GEM-4). Extending this scheme to finite-size scaling studies also allows to accurately determine the critical point parameters and to verify that it belongs to the Ising universality class.