Study of the Gruneisen parameters of optical modes for quartz, diamond, silicon, and germanium crystals

Isobaric $\gamma{i}^P$ and isothermal $\gamma{i}^T$ microscopic Gruneisen constants of quartz, diamond, silicon, and germanium crystals are calculated. It is shown that, from а comparison of $\gamma{i}^P$ and $\gamma_i{}^T$, the contributions bу phonon- phonon interactions and thermal expansion of а crystal to the temperature shift of the frequency of phonons can bе separated.