Pui K. Lam

Ab initio calculation of the static structural properties of Be

Abstract An ab initio calculation of the static structural properties of Be is presented. The total structural energy is calculated using pseudopotentials and the local density-functional formalism with the atomic number as the only input. The lattice constant, Poissons ratio, and the bulk modulus are predicted by calculating the total energy of the system. The deviations of the calculated results for lattice constants c, a , and c/a are approximately 1% when compared with experimental results. Poissons ratio and the bulk modulus are also in reasonably good agreement with the measured values.

Temperature- and pressure-induced crystal phase transitions in Be

Beryllium is known to undergo a HCP-BCC transition at about 1530K and ambient pressure. This transition is studied theoretically by comparing the Gibbs free energies for the HCP, FCC and BCC modifications of Be. The static lattice energy is calculated using the ab initio pseudopotential method. The photon energy and entropy are estimated from the calculated elastic constants. A mechanism for this transition is proposed based on the results of the calculations. At high temperature, the BCC modification is found to be stabilised by the large entropy for this phase caused by the presence of soft phonon modes. Possible pressure-induced phase transitions are examined. At about 1-2 Mbar the FCC and BCC phases are both more stable than the HCP phase. The regions of FCC and BCC stability lie too close to be separated in the present calculation.

Effective radii and volumes for elements in A15 compounds

Abstract Atomic sized measured by radii and volumes are compared for elements in the A15 structures.

Dependence of lattice constants and bulk moduli on pseudopotential properties

Abstract Using a nearly-free-electron model and model pseudopotentials, an analytical relation between the Wigner-Seitz radius for a metal, r ws , and the core radius of the model pseudopotential, r c is derived. In addition, a semi-empirical formula for the bulk moduli is obtained.

Correlation of superconductivity with material properties

Abstract A simple model is used to study the trends of the electron-phonon interaction parameter γ.