p, d and f bonds in elemental solids

Sound velocities of PbTe to 14 GPa: evidence for coupling between acoustic and optic phonons

Sound velocities of PbTe have been determined to 14 GPa using an ultrasonic interferometric method, which allowed for a detailed investigation of the characteristic variations of P and S wave velocities across the phase transitions from Fm3¯m (B1) to the orthorhombic Pbnm to Pm3¯m (B2). Elastic bulk and shear moduli and their pressure derivatives have been determined by fitting the measured velocities using a finite-strain approach. Based on the measured velocities and Debye theory, an estimate is made of the acoustic phonon contribution to the thermal conductivity, considering inter-phonon interactions only. By combining this result with previous determinations of the thermal conductivity due to electrons, the combination was found to have a significantly lower value than the previously determined total thermal conductivity. This is interpreted as evidence for coupling between the low-lying transverse optic (TO) and longitudinal acoustic (LA) modes, allowing the transfer of thermal energy from the acoustic to the optic modes. Possible explanations are discussed in the paper.

Electronic structure and magnetic properties of solids

We review basic computational techniques for simulations of various magnetic properties of solids. Several applications to compute magnetic anisotropy energy, spin wave spectra, magnetic susceptibilities and temperature dependent magnetisations for a number of real systems are presented for illustrative purposes.