The dihydrogen storage capacity of ScxNy (x + y = 4) compounds have been theoretically investigated at different levels. At B3LYP-D3/6-311G(3df,3pd) level, ScN3 has multiple isomers with similar energies, which is an interference of hydrogen storage research. Sc2N2 and Sc3N has four and three isomers, respectively. For both systems, the lowest-lying isomers are planar Sc2N2 01 and Sc3N 01, which are energetically much low-lying by at least 20 kcaVmol than the other isomers, respectively. Sc3N 01 can adsorb 8H(2) with gravimetric uptake capacity of 9.77 wt %. It satisfies the target specified by US DOE, however, some hydrogen molecules will dissociate and bond atomically on scandium atoms. The strong binding energy (0.66 eV/H-2) exceeds the reversible adsorption range (0.1-0.4 eV/ H2), which will cause high operating temperature to desorb hydrogen during the application process. Sc2N2 01 can adsorb 9H(2) in the molecular form. The H-2 gravimetric uptake capacity of Sc2N2 01 (9H(2)) (13.33 wt %) exceeds the target set by US Department of Energy, moreover, its average adsorption energy (0.32 eV/H-2) is in the reversible adsorption range. The interaction of Sc2N2 01 with H2 molecules is considered by means of the bond critical points (bcp) in the quantum theory of atoms in molecules (QTAIM). The Gibbs free energy corrected adsorption energy points that the adsorption of Sc2N2 01(9H(2)) is energetically favorable below 240 K. Therefore, in ScxNy (x + y = 4), the planar compound Sc2N2 01 is more suitable to be a dihydrogen adsorption material. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.