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The variation of the electronic Gruneisen parameter ( gamma e) is evaluated for the high-atomic-number elements thorium and lead by use of the relativistic augmented-plane-wave method and the pseudopotential method respectively. The variation of gamma e in thorium is found to be in qualitative agreement with that obtained from the Thomas-Fermi atom model, but the variation in lead is found to be in the opposite direction. The thermal electronic energy for thorium is also found to depart from the T2 behaviour often assumed in shock-wave calculations.

The shock Hugoniot equation of state for thorium has been computed, using the pseudopotential methods. The nuclear Gruneisen parameters ( gamma ), used in evaluating the ionic vibration contributions have been derived from phonon frequencies. The electronic thermal contribution is obtained using Thomas-Fermi-Dirac (TFD) theory, as the electronic Gruneisen parameter varied with temperature in accordance with TFD theory. The computed P-V curves is in agreement with the data of McQueen and Marsh (1960) although the Hugoniot temperatures at high compressions are different from those derived by them.

In the structural map for dialuminides based on Miedema parameters, the compound ThAl2, which crystallises in the AlB2 structure at ambient conditions, falls in the region of Laves phase (MgCu2) compounds. The authors have shown that only moderate pressure is required to transform it to the structure predicted by the structural map.

The metal beryllium (Be) has been studied under high pressure using an electrical resistivity technique with in situ pressure calibration. A sluggish phase transition at 12 GPa is observed which the authors identify as the HCP to distorted HCP phase transition reported in a recent high-pressure X-ray diffraction study. However, a reanalysis of the X-ray data on the high-pressure phase Be(II) indicates that a smaller orthorhombic cell with four atoms fits the observed interplanar spacings. The observed intensity ratios of the diffraction lines can be explained reasonably well on the basis of the space group P21212 with four Be atoms occupying 4c positions.