Population Analysis of Sodium Chloride Crystals Having Unusual Stoichiometries

Recently, Zhang et al. (Science, Dec. 2013, Vol. 342, pp. 1502-1505) predicted and synthesized crystals of sodium chloride compounds that have novel stoichiometries under high pressure conditions (in excess of 1 million atmospheres of pressure): NaCl₇, Na₃Cl, Na₂Cl, Na₃Cl₂, NaCl, and NaCl₃. We used the Density Derived Electrostatic and Chemical (DDEC) and Bader atomic population analysis methods to study atomic charge states and bonding between atoms in Zhang et al.’s ten published crystal structures. The computed DDEC effective bond orders showed that in several of these structures the chlorine atoms bond to form chains along the crystals, which confirms Zhang et al.’s electron localization function (ELF) results. Bader and DDEC net atomic charges are also compared and discussed for these crystals.