Partial electron localization functions ELF(sigma_loca), ELF(pi) and ELF(sigma_delo) of boron B-n and silicon MSi12 double ring (DR) clusters were analyzed. In a DR, separated basins are localized within peripheral bonds (sigma), delocalized outside inner bonds (pi), or delocalized above and below peripheral bonds (sigma). MO spectrum of skeleton D-6h Si-12 DR follows delightfully the hollow cylinder model. A mixture of different sets of MOs makes the D-6h Si-12 structure highly unstable. Upon interacting with 3d orbitals of Cr dopant, such a mixed behavior of MO sets is removed and the Cr@Si-12 DR becomes a global minimum structure. (C) 2017 Elsevier B.V. All rights reserved.