Compounds of superatom clusters: preferred structures and significant nonlinear optical properties of the BLi6-X (X = F, LiF2, BeF3, BF4) motifs.

A new type of superalkali-(super)halogen compound, BLi6-X (X = F, LiF2, BeF3, BF4), is theoretically predicted. The interaction between superalkali BLi6 and different shaped superhalogen X is found to be strong and ionic in nature. Bond energies of these BLi6-X species are in the range of 151.3-220.6 kcal/mol at the CCSD(T)/aug-cc-pVDZ level, which are much larger than the traditional ionic bond energy of 130.1 kcal/mol for LiF. Furthermore, because of their delocalized electron character, these superalkali-(super)halogen species exhibit extraordinarily large first hyperpolarizabilities with beta0 ranging from 5166.5 to 17791.0 au. Besides, the examination of the variation of nonlinear optical (NLO) properties with the size of (BLi6-BeF3)n assemblies shows the dependence of NLO properties on the chain length of (BLi6-BeF3)n. The present investigation gives hints to scientists in extending the research in atomic dimension to direct the interaction between superatoms, and using superatoms as building blocks to synthesize novel meaningful materials with unusual properties such as nonlinear optical properties.