Comment on ‘‘Constant pressure molecular dynamics algorithms’’ [J. Chem. Phys. 101, 4177 (1994)

Abstract

In this comment we point out the differences between the NPT ensemble techniques proposed in references [S. Melchionna, G. Ciccotti, and B. L. Holian, Mol. Phys. 78, 533 (1993)] and [W. G. Hoover, Phys. Rev. A 31, 1695 (1985)], i.e., the revised form and the original form of the Hoover NPT dynamics. We show that our dynamics generates exactly the isobaric–isothermal distribution function for a system with (N−1) particles (similarly to what happens with the molecular dynamic (MD) microcanonical ensemble in which the total momentum is conserved). Moreover we show numerically that in the original Hoover dynamics, i.e., the one leading to an incorrect distribution function, the Nosè variable thermalizes the center-of-mass velocity while that is exactly what does not happen with our dynamics which produces the correct isobaric distribution.