Preliminary calculations on the isomers of (CdSe) 13 have shown that the PBE/DZ level of theory is able to reproduce the geometry delivered by the much expensive B3LYP/def2-TZVP (1144 Basis Functions for (CdSe) 13 ), see Table 1 . Regarding the DZ basis set, enlarging the size of the frozen core from 3d /3p (small core) to 4p/3d (medium core) for Cd/Se atoms speeds up calculations remarkably but worst geometries are obtained. For the B3LYP functional, the performance of smaller sets has been

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... ted, namely LANL2DZ (338 BFs), LANL2DZ* (442 BFs), SBKJC-VDZ (507 BFs) and SBKJC-VDZ* (637 BFs). LANL2DZ* and SBKJC-VDZ* include extra d orbitals for Se atoms as compared to the parent LANL2DZ and SBKJC-VDZ sets, given the importance of the polarization functions for the proper description of the highly-coordinated atoms in three-dimensional clusters [1, 2] . LANL2DZ is probably the most widely employed basis set to model CdSe nanostructures [3, 4, 5, 6, 7] . For the small (CdSe) 13 clusters studied here, it has shown to overestimate Cd-Se bond lengths, leading to an improper description of structure and energetics as compared to reference B3LYP/def2-TZVP calculations. This finding agrees with previous results by Nguyen and co. on [2] . For bigger (CdSe) n nanoclusters, the LANL2DZ set could benefit from basis sharing effects. The inclusion of d polarization functions for Se atoms slightly corrects the behavior of LANL2DZ. The SBKJC set previously employed for the characterization of CdSe nanoclusters provide better geometries [1, 2] . Again, extra polarization functions lead to the improvement of the geometry. The inclusion of the Grimme's dispersion terms [8] produce little changes on the geometry of the bare (CdSe) 13 isomers, see Table 2 . For the ligand-capped structures, on the contrary, the dispersion corrected PBE-D3 provides remarkably shorter nanocluster-ligand bonds than the parent PBE, see Table 3 . Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics This journal is