On the inadequacy of linear pressure dependence of vibrational frequency

The pressure behaviour of vibrational frequencies was discussed in a recent paper by Liu [Solid State Commun. 114 (2000) 637]. It was found that the assumption of a linear pressure dependence is not justified, and it was concluded that the Murnaghan equation-of-state (EOS) is inadequate for solids. In contrast, here it will be shown that the linear pressure dependence provides no difficulties when introduced correctly and that the Murnaghan EOS can be used consistently.