A theoretical study of the crystal HgCl2 compound

A theoretical study of the crystal HgCl2 compound has been done using a qua si-relativistic density-functional method. The crystalline environment was simulated by a cut-off type Madelung potential. Bond length, dissociation e nergy, force constants, and sublimation enthalpy are calculated. The calcul ated properties are in goon agreement with available experimental data. The calculated difference in bond length between the isolated and crystalline molecule is consistent with the data obtained by the more recent gas-phase electron diffraction and X-ray single crystal measurements. The predicted s ymmetrical and antisymmetrical force constants (k(s), k(as)) and their tren d (k(as) > k(s)) are in accordance with the Raman and IR data. The trend is in contrast to the free molecule case, where k(as) < k(s). The sublimation enthalpies of hypothetical HgX2 (X = F, Cl, Br, I) compounds with the XeF2 -type structure are evaluated. It is shown that the XeF2-type structures fo r HgX2 are significantly less stable than the actual structures.