Electronic structure of NiO∕Ag(100) thin films from DFT+U and hybrid functional DFT approaches

The electronic properties of unsupported and supported NiO films on Ag(100) have been studied theoretically using two methods. Results from density functional theory using the $\mathrm{GGA}+\mathrm{U}$ approach and plane wave basis sets have been compared with those obtained with a hybrid functional and an atomic orbital basis set. In general the two approaches provide similar answers, with the exception of the NiO band gap which is better reproduced in the hybrid DFT approach. Both unsupported and supported films have an antiferromagnetic ordering, and only the magnetization of the Ni ions at direct contact with the metal substrate is slightly reduced, the rest being basically unperturbed. At variance with $\mathrm{Mg}\mathrm{O}∕\mathrm{Ag}(100)$ interfaces, NiO films adhere to Ag(100) with a bonding which includes also important covalent contributions. This results in a much smaller work function change than in $\mathrm{Mg}\mathrm{O}∕\mathrm{Ag}(100)$ and in tails of the NiO states which contribute to the density of states at the Fermi level.