Transition-metal dioxides: A case for the intersite term in Hubbard-model functionals

Abstract

Triatomic transition-metal oxides in the "inserted dioxide" (O-M-O) structure represent one of the simplest examples of systems that undergo qualitative geometrical changes via subtle electronic-structure modulation. We consider here three transition-metal dioxide molecules (MO(2) where M = Mn, Fe, or Co), for which the equilibrium structural (e.g., bent or linear geometry) and electronic (e.g., spin or symmetry) properties have been challenging to assign both theoretically and experimentally. Augmenting a standard density-functional theory (DFT) approach with a Hubbard term (DFT+U) occasionally overlocalizes the 3d manifold, leading to an incorrect bond elongation and, in turn, poor equilibrium geometries for MO(2) molecules, while preserving good spin-state splittings. Proper description of both geometry and energetics for these molecules is recovered; however, through either calculating DFT+U relaxations at fixed M-O bond lengths or by inclusion of an intersite interaction term V that favors M(3d)-O(2p) interactions. In this latter case, both U and V are calculated fully from first-principles and are not fitting parameters. Finally, we identify an approach that more accurately determines the Hubbard U over a coordinate in which the covalent character of bonding varies.

Evolutionary Algorithm‐Based Crystal Structure Prediction for Copper(I) Fluoride

“…A hybrid DFT‐PBE0 functional with 25 % Hartree–Fock exchange was utilized . For a 3d metal such as Cu, the use of hybrid DFT over GGA or GGA+ U is expected to increase the accuracy of the predictions . All‐electron, Gaussian‐type triple‐ ζ ‐valence + polarization (TZVP) and split‐valence + polarization (SVP) basis sets based on Karlsruhe def2 basis sets were used within the crystal structure predictions (a list with of all used basis sets is provided as SI) .…”

“…[35,36] For a3 dm etal such as Cu, the use of hybrid DFT over GGA or GGA + U is expected to increase the accuracy of the predictions. [37][38][39][40][41][42][43] All-electron, Gaussian-type triple-z-valence + polarization (TZVP) and split-valence + polarization (SVP) basis sets based on Karlsruhe def2 basis sets were used within the crystal structure predictions (a list with of all used basis sets is provided as SI). [44] Cu I ions are expected to show weak "cuprophilic" d 10 -d 10 interactions, [45][46][47][48] which were taken into account in the USPEX search using Grimme's D3 dispersion correction with zero-damping (ZD).…”

Perspective: Treating electron over-delocalization with the DFT+U method

“…Typically, calculated values of U do not exclude bonding, but sufficiently large values of U will elongate bonds and alter angular potentials leading to qualitative changes in geometry. 80 Instead, alternative methods include constraining bonds, 80 varying U along the bonding coordinate 64 or considering intersite terms 80 (i.e., V ) is necessary.…”

Role of electronic localization in the phosphorescence of iridium sensitizing dyes

“…transition-metal oxides), but also in cases where electrons are delocalized (e.g., band insulators) [41]. The V correction has also proved to be crucial in obtaining accurate structural properties of transition-metal dioxide molecules [71], and in describing the dimerization of V atoms in VO 2 accross the high-temperature to low-temperature phase transition through a DMFT approach [72]. In Ir complexes, while the on-site interaction U helps capturing the localization of d electrons on the central Ir atom, the inter-site V is expected to improve the description of the interactions with the surrounding organic ligands.…”