The fractionation of Ca isotopes has been computed between various solids (calcite, dolomite, aragonite, lime CaO, diopside, grossular) based on six different DFT-based theoretical schemes (PZ, PBE, vdW-DF2, BLYP, BLYP + Grimme-D2 correction, and PBEsol). The results strongly depend on the selected theoretical scheme, with almost 2 differences in some cases, for isotope fractionations varying by 8 overall. Based on several quality criteria (accuracy and consistency of the error on structure and vibrations in particular), the PBEsol functional appears more accurate and more consistent than the others, with PZ and VdW-oriented functionals behaving particularly badly. The possibilities for correction based on experimental frequencies were evaluated in details, pushing further the principle of frequency rescaling. Even for exceptional cases where the