504 publications from this institution
The $G\phantom{\rule{0}{0ex}}W$ method of Lars Hedin is the most popular approach to predict electron addition and removal energies in solids. To date, most $G\phantom{\rule{0}{0ex}}W$ calculations are performed assuming that the many-body system features sharp resonances, also known as quasiparticle peaks. The authors go beyond this approximation and determine the Green's function $G$ and the screened interaction $W$ fully self-consistently in the $G\phantom{\rule{0}{0ex}}W$ approximation. They find strong broadening of the quasiparticle peaks. Somewhat disappointingly, the predicted band gaps are too large. This notwithstanding, the work is an important step towards a full solution of Hedin's equations.
We present a detailed study of the lattice dynamics and of the phase stability of cubic zincblende (c-BN) and hexagonal (h-BN) boron nitrides. The phonon-dispersion relations at different densities are calculated using a first-principles force-constant method. The calculated eigenfrequencies and phonon Gr\"uneisen parameters are in good agreement with experimental findings. From the electronic and vibrational energies as a function of volume we calculate the phase $(p,T)$ diagram of boron nitride in a quasiharmonic approximation. At low temperature c-BN is the stable modification; the c-BN/h-BN coexistence line intersects the temperature axis at 1440 K. In experiments this temperature lies between 1200 and 1800 K. Anharmonic corrections improve the agreement between the calculation and experiment for high pressure and temperature.
