A MOLECULAR DYNAMICS STUDY OF THE BEHAVIOR OF SODIUM IN LOW ALBITE

Abstract

The structural features of albite (atomic coordinates and distances, thermal displacements) at 25 and 1040 'C, obtained by Molecular Dynamic simulations following the Car-Parrinello approach, were favorably compared with those obtained by single-crystal diffraction experiments. Starting from this basis, it was shown that the marked anisotropy of electron density distribution about the positions of the sodium atoms is due to a time average of highly anisotropic thermal vibrations, and not to a space average of multiple positions occupied by Na. Although the large displacement of Na from its center of gravity results in great variations over time of the individual Na-0 distances of the sodium coordination polyhedron, the average distance remains approximately constant, reaching its minimum variation when the 9 nearest 0 atoms are considered, thus supporting a true 9-coordination of sodium.