Improved method for predicting thermodynamic properties—KBr

A method is described for predicting the thermodynamic properties of crystals that accounts for the effect of anharmonicity on the bulk modulus and on the equilibrium condition. An iterative procedure is used that makes the predicted room-temperature values for the bulk modulus and the nearest-neighbor distance self-consistent with the experimental values. Formulas are given for determining both the temperature and pressure dependence of the coefficient of thermal expansion $\alpha$, the heat capacities $C_v$ and $C_p$, the bulk moduli $B_T$ and $B_S$, and the pressure derivatives ${\left(\frac{\partial B_T}{\partial P}\right)}_T$ and ${\left(\frac{\partial B_S}{\partial P}\right)}_T$. The method is applied to KBr, and very good agreement is obtained with the experimental values for $\alpha$ and $C_p$ over a wide range of temperatures without adjustable parameters. The Cauchy relation $C_{44}=C_{12}$ is discussed, and the macroscopic Grüneisen ratio $\gamma \mathrm{}\left(T\right)\mathrm{}$ is calculated.