The Fourier transform of the X-ray diffraction pattern of a crystal is the electron density of the crystal averaged over space and time. In the determination of the structure of a crystal this electron density is modeled by a set of spheres of electron density representing the atoms together with a »smearing function«, the atomic displacement parameters, representing the motion (translation and...

We present the results of studying electronic, elastic, vibrational, and thermodynamic properties of type-VIII clathrates Ba 8 Ga 16 Sn 30 Ba 8 Al 16 Sn 30 calculated from a first-principles approach. The calculations utilize the generalized gradient approximation to density functional theory. The results indicate that the Ba 8 Ga 16 Sn 30 and Ba 8 Al 16 Sn 30 are indirect semiconductors with f...

Cometary nuclei are considered to most closely reflect the composition of the building blocks of our solar system. As such, comets carry important information about the prevalent conditions in the solar nebula before and after planet formation. Recent measurements of the time variation of major and minor volatile species in the coma of the Jupiter family comet 67P/Churyumov-Gerasimenko (67P) by...

Computational studies are presented examining the degree of proton disorder in argon and molecular hydrogen sII clathrate hydrates. Results are presented using a variety of model potentials for the dielectric constant, the proton order parameter, and the molecular volume for the clathrate systems. The dielectric constant for the clathrate systems is found to be lower than the dielectric constan...

The use of high-pressure for the study and elaboration of homogeneous nanostructures is critically reviewed. Size effects, the interaction between nanostructures and guest species or the interaction of the nanosystem with the pressure transmitting medium are emphasized. Phase diagrams and the possibilities opened by the combination of pressure and temperature for the elaboration of new nanomate...

The crystal structures of the Werner clathrates Ni(NCS)2(isoquinoline)4 (H) with para-xylene (px), meta-xylene (mx) and ortho-xylene (ox) have been elucidated. The kinetics of thermal decomposition of the three inclusion compounds were performed using the isothermal technique of Flynn and Wall. Selectivity of H for the xylene isomers was determined for both the liquid and vapour phase binary mi...