The aforementioned occupational Ni/V site disorder of the Ni 4 V 3 O 10 phase is challenging to model computationally because the periodic boundary conditions cannot be imposed in the same way as in perfect crystals. To simulate this material, the unit cell derived from the powder X-ray diffraction experiments as shown in Fig. was the starting point. As listed in Table , two sites, Ni1/V1 and Ni2/V2, have site disorder with Ni as the sites' primary element. Based on Ni:V occupancy ratios of about 0.8:0.2 and 0.7:0.3 for Ni1/V1 and Ni2/V2 sites, respectively, and taking into account that the Ni1/V1 site includes 8 atoms while the Ni2/V2 site hosts 2 atoms, all possible configurations in which 8 of these doubly occupied sites are filled with Ni and 2 of them are filled with V were found. This is a simple combinatorial problem leading to 10 2 = 45 configurations, which reduce to 8 symmetrically distinct classes (see Table ). For all of these, band structures, projected electronic densities of states, and dielectric functions were computed and are discussed below.