First-Principle Calculations for Elastic and Thermodynamic Properties of Diamond

The elastic constants and thermodynamic properties of diamond are investigated by using the CRYSTAL03program. The lattice parameters, the bulk modulus, the heat capacity, the Griineisen parameter, and the Debye temperatureare obtained. The results are in good agreement with the available experimental and theoretical data. Moreover, therelationship between V/V;and pressure, the elastic constants under high pressure are successfully obtained. Especially,the elastic constants of diamond under high pressure are firstly obtained theoretically. At the same time, the variationsof the thermal expansion a with pressure P and temperature Tare obtained systematically in the ranges of 0-870 GPaand 0-1600 K.