Improvement of d–d interactions in density functional tight binding for transition metal ions with a ligand field model: assessment of a DFTB3+U model on nickel coordination compounds

Abstract

DFTB3+U for transition metal systems.

Biomolecular QM/MM Simulations: What Are Some of the “Burning Issues”?

“…One possible improvement is to treat the d/f electrons separately, along the lines of the DFT+U model in materials science 59 or the ligand-field model in the inorganic chemistry literature. 60,61 In a recent explorative study, 62 together with collaborators we have implemented a preliminary version of the DFTB3+U model…”

“…Energetics are generally less satisfying, especially when considering different spin states, since interactions among d/f electrons are treated in an averaged fashion in the current tight-binding models. One possible improvement is to treat the d/f electrons separately, along the lines of the DFT+U model in materials science or the ligand-field model in the inorganic chemistry literature. , In a recent explorative study, together with collaborators we have implemented a preliminary version of the DFTB3+U model in which P U ( P I ) is the spin unpolarized (polarized) density matrix element involving the d/f electrons and the usual two-electron integrals are parametrized in terms of the Slater integrals or the Racah parameters . It was found that the additional U contribution indeed improved the splitting between the low-spin and high-spin states in a series of Ni­(II) and Ni­(III) compounds as well as the populations of the 3d orbitals .…”

“…One possible improvement is to treat the d/f electrons separately, along the lines of the DFT+U model in materials science or the ligand-field model in the inorganic chemistry literature. , In a recent explorative study, together with collaborators we have implemented a preliminary version of the DFTB3+U model in which P U ( P I ) is the spin unpolarized (polarized) density matrix element involving the d/f electrons and the usual two-electron integrals are parametrized in terms of the Slater integrals or the Racah parameters . It was found that the additional U contribution indeed improved the splitting between the low-spin and high-spin states in a series of Ni­(II) and Ni­(III) compounds as well as the populations of the 3d orbitals . Further self-consistent tuning of the electronic parameters in the model will be informative regarding the degree of transferability and expected accuracy for the +U model, and whether a multideterminant formulation of the DFTB3 model (e.g., in the framework of ensemble or multistate DFT) is warranted.…”

“…(b) Examples of frontier orbital comparisons between DFTB3, DFTB3+U, and PBE calculations for high-spin [Ni­(H 2 S) 6 ] 2+ . Including the +U correction in DFTB3/3OB improves various properties such as d orbital populations, nature of frontier orbitals, ligand-field splitting, and energy difference between low-/high-spin states.…”

Tetrahedral Cyclopentadienylmetal Carbonyl Clusters of Manganese and Chromium: A Theoretical Study

“…The OPBE functional was chosen for this research since it is one of the best DFT functionals for accurate prediction of vibrational frequencies, reaction barriers, spin-state splittings, and geometries. − Energies and gradients were calculated using the local density approximation (LDA; Slater exchange and Vosko–Wilk–Nusair (VWN) correlation) with nonlocal corrections due to Handy–Cohen (OPTX exchange), , and Perdew–Burke–Ernzerhof (PBEc correlation) added self consistently . The spin-state splitting predicted by OPBE gives the correct spin ground state in almost all cases, except for the iron–porphyrin with an axial histidine ligand.…”