Ab initioabsorption spectrum of NiO combining molecular dynamics with the embedded cluster approach in a discrete reaction field

Abstract

We developed a procedure that combines three complementary computational methodologies to improve the theoretical description of the electronic structure of nickel oxide. The starting point is a Car-Parrinello molecular dynamics simulation to incorporate vibrorotational degrees of freedom into the material model. By means of complete active space self-consistent field second-order perturbation theory (CASPT2) calculations on embedded clusters extracted from the resulting trajectory, we describe localized spectroscopic phenomena on NiO with an efficient treatment of electron correlation. The inclusion of thermal motion into the theoretical description allows us to study electronic transitions that, otherwise, would be dipole forbidden in the ideal structure and results in a natural reproduction of the band broadening. Moreover, we improved the embedded cluster model by incorporating self-consistently at the complete active space self-consistent field (CASSCF) level a discrete (or direct) reaction field (DRF) in the cluster surroundings. The DRF approach offers an efficient treatment of electric response effects of the crystalline embedding to the electronic transitions localized in the cluster. We offer accurate theoretical estimates of the absorption spectrum and the density of states around the Fermi level of NiO, and a comprehensive explanation of the source of the broadening and the relaxation of the charge transfer states due to the adaptation of the environment.

Determination of the optical gap bowing parameter for ternary Ni1−xZnxO cubic rocksalt solid solutions

“…[1][2][3]31 The value of E g,ZnO in the RS structure which is reported in the literature is 2.45 ± 0.15 eV, measured by performing pressure dependent absorption measurements on ZnO thin films. The value of E g,NiO in the RS structure is 3.85 ± 0.03 eV as determined in the present study, which is in good agreement with the values reported in the literature.…”

“…4,31 The leading absorption edge observed in NiO is related to the ligand to metal charge transfer (ligand O-2p to metal Ni-3d orbitals), which is termed as the optical gap. Thus, a plot between [F(R ∞ ) × hν] n versus hν yields a straight line and the intercept on the energy axis gives the value of the bandgap.…”

Orbital reconstruction in nonpolar tetravalent transition-metal oxide layers

“…To obtain a clear picture on crystal-field effects and spin-orbit interactions at the central Ir site, we cutoff the magnetic couplings with the adjacent Ir ions by replacing the tetravalent open-shell d 5 NNs with tetravalent closed-shell Pt 4+ species. This is a usual procedure in quantum chemistry studies on TM systems, see for example, refs 42 , 45 , 53 , 54 , 55 , 56 . We used energy-consistent relativistic pseudopotentials and valence basis sets of quadruple-zeta quality supplemented with f polarization functions for the central Ir ion 57 and all-electron triple-zeta basis sets for the six adjacent ligands 58 .…”

On the Synergism between Cu and Ni for Photocatalytic Hydrogen Production and their Potential as Substitutes of Noble Metals

“…NiO cannot trap photogenerated electrons because the conduction band of NiO is more negative than that of TiO 2 . There is some controversy in the literature about the valence and conduction band energies of NiO . Values in the ranges of −0.3 to −1.0 eV are reported for the conduction band, and 2.4 to 4.3 eV for the valence band (with respect to the standard hydrogen electrode (SHE)) .…”