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Mondal, Swastik ; van Smaalen, Sander ; Schoenleber, Andreas ; Filinchuk, Yaroslav ; Chernyshov, Dmitry ; et. al. Electron-Deficient and Polycenter Bonds in the High-Pressure gamma-B-28 Phase of Boron. In: Physical Review Letters, Vol. 106, no. 21, p. 215502 (2011)