The Role of Local DFT+U Minima in the First-Principles Modeling of the Metal–Insulator Transition in Vanadium Dioxide

Abstract

The DFT+U method is frequently employed to improve the firstprinciples description of strongly correlated materials. However, it is prone to deliver metastable electronic minima. While these local minima of the DFT+U method are often considered to be computational artifacts, their physical meaning and relationship to true excited states remains unclear. In this work, the possibility of theoretically modeling transformations in the solid state that require thermal or optical excitations of electrons is explored, taking into account the metastable states of the computationally undemanding DFT+U formalism. For this purpose, we choose to examine the example of the VO 2 metal−insulator transition. Metastable states that are located on different electronic potential energy surfaces are found to correspond to experimentally observed VO 2 phases. The identified metastable electronic states can be used to model the collapse of the VO 2 band gap at elevated temperatures and upon photoexcitation as well as other monoclinic−monoclinic phase transformations. The results suggest that local DFT+U minima can indeed carry physical meaning, while they remain under-reported in theoretical literature on transition metal oxides like VO 2 .

Magnetism between magnetic adatoms on monolayer NbSe2

“…This is due to the fact that NbSe 2 monolayer is metallic, which increases the hybridization of the 3d states of the impurity and therefore diminishes their atomic-like character. This is particularly important for DFT+U calculations, which may lead to a plethora of local minima for atomiclike systems as adatoms [73,74]. Since the N + and N − configurations arise also without spin polarization (see appendix A), they cannot be considered as metastable spin states.…”