Evolutionary searches using the USPEX method (Universal Structure Predictor: Evolutionary Xtallography) combined with density functional theory (DFT) calculations were performed to obtain the global minimum structures of beryllium (Ben, n=3-25)...

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Calculated steric charges (q s r ð Þ ¼ À1 4p r 2 u s r ð Þ, where n s is steric potential) on the molecular surfaces are used to investigate the non-covalent interactions formed between some RÀX molecules (R = NC, NCCC, CF 3 CC, FCC, CF 3 , CH 3 , and X=F, Cl, Br) and ammonia, water as well as formaldehyde. It is shown that the formation of halogen-bonded complexes could be regarded as the interaction between a negative steric charge (steric potential depletion) on the surface of halogen atom and a positive steric charge (steric potential accumulation) region of an electron-donor site. But the evaluated positive steric charges on the surface of fluorine atoms in RÀF molecules predict no halogen bonds for these compounds. Therefore, it is suggested that the R< CÀ >FÁ Á ÁY interactions should be renamed to "fluorine bond", instead of halogen bond. The evaluated steric charges also successfully determine both the strength and direction of halogen bonds for those cases in which the s-hole concept fails.