PREDICTION OF STRUCTURAL PARAMETERS AND PHYSICAL-PROPERTIES OF CSHSO3UP TO 60 GPA

Ab initio calculations based on density-functional theory have been us ed to predict the position of the hydrogen atom in CsHSO3 and the pres sure dependence of structural parameters and physical properties up to 60 GPa. For the calculations, a generalized gradient approximation, p seudopotentials, and a constant pressure relaxation based on a Broyden -Fletcher-Goldfarb-Shanno algorithm were used. At ambient pressure all calculated structural parameters coincide within 3% with experimental data. The S-H stretch frequency calculated within a frozen-phonon app roach matches experimental observations within 2%. The present calcula tions predict a tetrahedral HSO3- ion with a S-H distance of 1.35 Angs trom. Above 20-30 GPa a framework of HSO3- units, interconnected by tr ifurcated S-H ... O bonds, forms. The pressure dependence of optical p roperties was also predicted: for 0 (60) GPa the calculations give a d ouble refraction of -0.046 (-0.025) and a dispersion of 0.013 (0.018). [S0163-1829(98)01107-2].