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The introduction of fluorine(F)into the borate crystals is proven to be an effective approach in designing novel non-centrosymmetric crystals,which is a requirement for nonlinear optical(NLO)materials.In this contribution,the electronic structure and optical properties of borate fluoride crystals are determined by the first-principles method.First-principles calculations indicate that the key second-harmonic generation(SHG)factor is attributed not only to borate groups but also to the bonding of the F anions with cations where F coordinates to cations(Sr,Ba).The electron withdrawing effect of the F atom leads to the higher values for anisotropy of the polarizability around cation-centered polyhedra,ultimately making it easy for the external electric field of incident light to effect the dielectric susceptibility.The direct contribution of anion on the NLO properties is observed as fluorine-induced variation of electronic structure.