材料期刊网

The structural stability, thermodynamic, electronic, and optical properties of NaH with rock salt (B1) structure and cesium chloride (B2) structure under high pressure are investigated by first-principles calculations using norm-conserving pseudopotential applying a generalized gradient approximation (GGA) for exchange and correlation. Through the analysis of energy-volume variation, we find the phase transition of NaH from B1 to B2 structure occurs at 32.3 GPa, which in good agreement with the diamond-anvil-cell high-pressure experimental value of 29.3 +/- 0.9 GPa [Phys. Rev. B 36 (1987) 7664). By using the quasi-harmonic Debye model, the thermodynamic properties including the Debye temperature Theta(D), heat capacity C-V, thermal expansion coefficient alpha, and Gruneisen parameter gamma are successfully obtained in the temperature range from 0 to 700K and pressure ranges from 0 to 32 GPa and 33 to 100 GPa for NaH B1 and B2 phases, respectively. Analysis of band structures suggests that the NaH has an indirect band gap that the valence band maximum is at the W point and the conduction minimum locates at L point. The calculated energy gaps is very close to that value obtained in recent full potential augmented plane wave calculations. The optical properties including dielectric function epsilon(omega), absorption coefficient alpha(omega), reflectivity coefficient R(omega), and refractive index n(omega) are also calculated and analyzed. (C) 2012 Elsevier B.V. All rights reserved.