Electronic structure of stoichiometric and reduced ZnO from periodic relativistic all electron hybrid density functional calculations using numeric atom‐centered orbitals

Abstract

The atomic and electronic structure of stoichiometric and reduced ZnO wurtzite has been studied using a periodic relativistic all electron hybrid density functional (PBE0) approach and numeric atom-centered orbital basis set with quality equivalent to aug-cc-pVDZ. To assess the importance of relativistic effects calculations were carried out without and with explicit inclusion of relativistic effects through the zero order regular approximation. The calculated band gap is ~0.2 eV smaller than experiment, close to previous PBE0 results including relativistic calculation through the pseudopotential and ~0.25 eV smaller than equivalent non-relativistic all electron PBE0 calculations indicating possible sources of error in non-relativistic all electron density functional calculations for systems containing elements with relatively high atomic number. The oxygen vacancy formation energy converges rather fast with the supercell size, the predicted value agrees with previously hybrid density functional calculations and analysis of the electronic structure evidences the presence of localized electrons at the vacancy site with a concomitant well localized peak in the density of states ~0.5 eV above the top of the valence band and a significant relaxation of the Zn atoms near to the oxygen vacancy. Finally, present work shows that accurate results can be obtained in systems involving large supercells containing up to ~450 atoms using a numeric atomic centered orbital basis set within a full all electron description including scalar relativistic effects at an affordable cost.

Bandgap engineering by cationic disorder: case study on AgBiS2

“…To prove that, accurate ab initio density functional theory (DFT) simulations have been carried out for the semiconductor (matildite) and metallic limit cationic arrangements, as well as for a total of 26 different cationic disorders, randomly generated by successive Ag-Bi site permutations within the crystal unit cell. Notice that such a large phase sampling ensures a proper description of the structural diversity when cations are free to exchange their positions, as observed at the phase transition temperature of 610 K, 9 and well surpasses previous analysis of cationic arrangement on I-V-VI 2 compounds, where only a few specific positions, still with a high degree of ordering, were contemplated, [8][9][10][11][12][13][14][15][16] thus biasing the results to a very narrow region of the configurational space.…”

“…Urbach tails are found when disorders or impurities as significant, 11 and should be discerned to point defects, such as low-concentration vacancies, which display discrete states within the otherwise unchanged materials bandgap. 12 Such tails are interpreted in terms of thermal fluctuations arising from temperature-dependent coupling of excitons and phonons, 13 although other authors affirm that the origin stems out from a dependence of the 3 bandgap with respect an appearing tail of the density of states (DOS) when having disordered systems. 14 Related to the above point, here we show that the photochemical response of AgBiS 2 is highly dependent on the specific cation arrangement, i.e.…”

On the H2interactions with transition metal adatoms supported on graphene: a systematic density functional study

“…Aside, we employed the Ab Initio Simulation Package -AIMS, 58,59 where electron density is described with a basis set of Numeric Atom-centered Orbitals (NAO), with light grid Tier-1 basis set options, a basis set quality comparable (or better than) to double-ζ plus polarization Gaussian Type Orbitals (GTO) aug-cc-pVDZ basis. 60 Last, we also carried out calculations on molecular models consisting of benzene and H 2 by means of Gaussian09. 61 We used here three dispersion methods; D2, D3, and D3BJ, employing NASA Ames ANO extended basis set to avoid Basis Set Superposition Error (BSSE).…”

Tailoring the Performance of ZnO for Oxygen Evolution by Effective Transition Metal Doping

“…Using a hybrid functional, such as PBE0, would be a better way to obtain a better bandgap without deteriorating the structure of ZnO [23] . However, calculations with hybrid functionals increase the computational costs by 1–2 orders of magnitude [19] .…”