Supplement Number 1

structures of C2v E4F4− (E = Li, Na, K, Rb, Cs) clusters, The lowest vibrational frequency and point group at seven classical theoretical levels for the Li4F4− and Na4F4− cluster; Structures of Li4F4− (1), Na4F4− (2), Li4F4 (3) and their lowest-lying isomers; Structural evolution of neutral C2v Li4F4 optimization; The optimized structure of Li4F4− (1) at the CCSD(T)/def2-TZVPP; Isomer interconversion and their barrier (ΔG, kcal mol-1) calculated at the PBE0-D3/aug-cc-pVTZ level; The QTAIM and ELF of Li4F4− (1); The results of EDA-NOCV and IQA for 1; Cartesian coordinates of structures reported in this work.