Comment on “Negative heat capacities and first order phase transitions in nuclei”

In a recent paper Moretto et al. [Phys. Rev. C 66, 041601 (2002)] claim that the negative heat capacities presented in our previously published paper [Chomaz, Duflot, and Gulminelli, Phys. Rev. Lett. 85, 3587 (2000)] are “artifacts” coming from the use of periodic boundary conditions in the lattice-gas calculations. We stress in this Comment that this claim is wrong: in Chomaz, Duflot, and Gulminelli we did not use periodic boundary conditions and anyhow the boundary conditions are irrelevant for the statistical ensemble used in Chomaz, Duflot, and Gulminelli. The second claim of Moretto et al. is that, because of the Coulomb repulsion, systems “with $A>60$ should present no anomalous negative heat capacities.” We show that this conclusion is contradicted by exact lattice-gas simulations including Coulomb forces which present negative heat capacities even for $A>200$.

Figure 1

Caloric curve for the lattice-gas Hamiltonian augmented with the Coulomb interaction in the microcanonical isobar ensemble $\left(\ln \lambda =-7,A=207,Z=82\right)$ from Ref. 15. The coupling between neighboring sites is fixed to $ϵ=5.5\text{MeV}$.