To assess the thermodynamic stability of NaxV2(PO4)3 with distinct Na-vacancy orderings at 0 K, we used the spin-polarized density functional theory (DFT), as implemented in VASP. The exchange-correlation was approximated by the strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation functional, with a U correction of 1.0 eV on all vanadium atoms to improve the localization of 3d electrons. The total energies were converged to within 10 -5 eV/cell, atomic forces (stresses) within 10 -2 eV/Å (0.29 GPa). The 1 st Brillouin zone was integrated over a G-centered k-point grid of 3 × 3 × 3 for all primitive structures containing 2 formula units (f.u.) with 42 atoms, a 1 × 3 × 3 k-point mesh for all supercells with 4 f.u. (84 atoms), and a 1 × 1 × 3 mesh for 8 f.u. (168 atoms). The valence electrons were treated in terms of plane-waves up to an energy cutoff of 520 eV, while projector augmented wave potentials were used to describe the core electrons, with Na 3s 1 , V_pv 3p 6 3d 4 4s 1 , P 2s 2 3p 3 , O 2s 2 2p 4 .