Inadequacy of linear pressure dependence of vibrational frequency

Both Raman and IR vibrational frequencies were often reported to be linearly dependent on pressure. Thus, many reported values of the pressure dependence of frequency for the various vibrational modes, (∂νi/∂P)T, were derived by linear regression of the experimental data. Although the linear treatment of the experimental data is statistically sound, it is theoretically unjustified. The results also imply that the Murnaghan equation of state is inadequate for solids.