First-principles calculations of the specific heats of cubic carbides and nitrides

Calculated specific heats of several carbides and nitrides with a B1 structure have been compared with those of experimental data up to 3000 K. The specific heats at constant pressure are calculated with the quasiharmonic approximation, using phonon dispersions calculated from direct method, and pseudopotential plane-wave method. The calculated results of HfC, TaC, TiC, ZrC, and ZrN are in excellent agreement with the experimental data up to 3000 K. For NbC, TiN, and VC, the calculated results are also in excellent agreement with the experimental data up to 2000 K, while they show an excessive rise over the experimental data above 2000 K. The deviation of the calculation from the experiment at high temperature is caused by instability of the B1 structure or anharmonic effect.