Incorporating static intersite correlation effects in vanadium dioxide through DFT+V

We analyze the effects on the structural and electronic properties of vanadium dioxide (VO₂) of adding an empirical inter-atomic potential within the density-functional theory+V (DFT+V) framework. We use the DFT+V machinery founded on the extended Hubbard model to apply an empirical self-energy correction between nearest-neighbor vanadium atoms in both rutile and monoclinic phases, and for a set of structures interpolating between these two cases. We observe that imposing an explicit intersite interaction V along the vanadium-vanadium chains enhances the characteristic bonding-antibonding splitting of the relevant bands in the monoclinic phase, thus favoring electronic dimerization and the formation of a band gap. We then explore the effect of V on the structural properties and the relative energies of the two phases, finding an insulating global energy minimum for the monoclinic phase, consistent with experimental observations. With increasing V, this minimum becomes deeper relative to the rutile structure, and the transition from the metallic to the insulating state becomes sharper. We also analyze the effect of applying the +V correction either to all or only to selected vanadium-vanadium pairs, and both in the monoclinic as well as in the metallic rutile phase. Our results suggest that DFT+V can indeed serve as a computationally inexpensive unbiased way of modeling VO₂ which is well suited for studies that, e.g., require large system sizes.

本研究旨在分析在密度泛函理论+V (DFT+V) 框架内加入经验性的原子间势能对二氧化钒 (VO₂) 的结构和电子性质的影响。我们采用基于扩展哈伯德模型的 DFT+V 机制，对金红石和单斜相中的最近邻钒原子以及介于这两种情况之间的结构集施加经验性的自能修正。观察发现，在钒-钒链上施加显式的局域间相互作用 V，可增强单斜相中相关能带的特征性成键-反成键分裂，从而有利于电子二聚化和能隙的形成。随后，我们探讨了 V 对两种相的结构性质和相对能量的影响，发现单斜相存在绝缘的全局能量最低点，这与实验观察结果相吻合。随着 V 的增加，这一最低点相对于金红石结构变得更深，金属到绝缘态的转变变得更加尖锐。此外，我们还分析了将 +V 修正应用于所有或仅应用于所选的钒-钒对，以及在大单斜相和金属金红石相中的影响。我们的结果表明，DFT+V 确实可以作为一种计算成本低廉且无偏的建模 VO₂ 的方法，非常适合需要大系统尺寸的研究。