Hybrid density functional theory study of vanadium monoxide

First-principles calculations of nondefective VO in the Fm3m structure based on a range of single-particle Hamiltonians containing varying amounts of exact exchange indicate that the ground electronic state is that of a d 3 high spin, antiferromagnetic (AF), Mott-Hubbard insulator with an AF, spin alignment of the local cation moments. This description remains essentially unchanged down to 10% exact exchange, and only for the pure density functional theory (DFT) potential is the AF 1 phase found to be metallic. Strong spin-lattice interaction is predicted with differences in lattice constant of up to 1.6% between AF, and FM (ferromagnetic) order. The AF 1 lattice constant is predicted to be ∼4.37 A, which is roughly 7% greater than the reported lattice constants for the defective material. The bulk modulus is comparable to those of CaO, MnO, and NiO. A mapping of total energies onto an Ising spin Hamiltonian containing both direct and superexchange interactions reveals the dominant magnetic interaction to be the direct coupling of antiferromagnetically aligned nearest-neighbor cation spins, which leads to the stability of the AF 1 phase. Direct coupling energies are found in the range - 11.1 to -44.3 meV as the proportion of exact exchange is reduced, leading to an estimated critical disorder temperature in the range 300-450 K. However, the limitations of such mapping are exposed by a consideration of the relative stabilities of the AF 1 and AF 3 alignments. Orbital projected densities of states reveal filled to unfilled gaps which depend strongly on the proportion of exact exchange and for the B3LYP potential (20% exact exchange) are ∼2.5 eV for the spin-forbidden xy(∩)→xy(↓) excitation, ∼ 3.0 eV for xy(∩) → z 2 (∩), and ∼3.5 eV for V→O charge transfer. Variationally stable, highly local crystal-field excited states ranging in energy from ∼0.6 to ∼2.7 eV are predicted for exchange-correlation potentials down to 30% exact exchange and from comparisons with the corresponding band excitation estimates of ∼1 to ∼2 eV are obtained for the localization energy of Frenkel excitons. From a mapping of the excited crystal-field energies onto a Kanamori Hamiltonian, values are obtained for the lattice Racah B and C parameters and the d-orbital averaged exchange and crystal-field energies. A comparison of mapped and directly calculated energies of the two-electron excitation (xz,yz)→(z 2 ,x 2 -y 2 ) confirms the validity of Kanamori mapping, notably in the limit of exact exchange.