Quantum effects on elastic constants of diamond by path-integral Monte Carlo simulations

Using the path-integral Monte Carlo method, we investigate the quantum effects on the elastic constants C-11, C-12, and C-44 of the diamond crystal in a wide temperature range at ambient pressure. The Tersoff potential is used to describe the interatomic interactions and the elastic constants are determined by a direct method derived from the stress-strain curve. We find that the elastic constants C-11 and C-44 behave as a quadratic function of temperature at low temperatures and C-12 is practically a constant being independent of temperature. The quantum effects are significant at low temperatures up to about 1000 K. The quantitative differences between the PIMC calculations and the experimental measurements of the elastic constants C-11, C-12, and C-44 at low temperatures are about 3%, 17%, and 9%, respectively. Using the obtained elastic constants, we also estimate the bulk modulus B, anisotropic factor A, Cauchy pressure P-Cauchy, and Poisson ratio v of the diamond crystal.