Structural stability and defect energetics of ZnO from diffusion quantum Monte Carlo

Santana, Juan A.; Krogel, Jaron T.; Kim, Jeongnim; Kent, Paul; Reboredo, Fernando A.

doi:10.1063/1.4919242

Cited by 58 publications

(75 citation statements)

References 118 publications

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“…In fact, recent calculations have shown that a 12.5% of Fock exchange is necessary to reproduce the band gap of stoichiometric TiO 2 rutile and anatase polymorphs, whereas within the HSE type of functional it is necessary to reduce it to 20% . Similar findings have been also recently reported for ZnO including very accurate diffusion quantum Monte Carlo calculations . This fact seems to be a consequence of the different dielectric constant of each material and, in fact, several authors suggested to use this property to define the amount of Fock exchange required to properly describe a given solid, although one needs to realize that such approach includes, in an empirical way, a macroscopic parameter external to theory, even if this can be done in a self‐consistent manner …”

Section: Models and Methodsmentioning

confidence: 59%

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

Viñes

2017

J Comput Chem

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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.

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Section: Models and Methodsmentioning

confidence: 59%

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

Viñes

2017

J Comput Chem

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“…The optimized pseudopotentials presented here have also been employed in a few recent studies of bulk transition metal oxides [65][66][67] as well as bulk metals 65,68 . For comparison with our dimer results, we reproduce the bulk data in Table IV with permission of the authors.…”

Section: Comparison With Bulk Studiesmentioning

confidence: 99%

Pseudopotentials for quantum Monte Carlo studies of transition metal oxides

2016

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Quantum Monte Carlo (QMC) calculations of transition metal oxides are partially limited by the availability of high quality pseudopotentials that are both accurate in QMC and compatible with major planewave electronic structure codes. We have generated a set of neon core pseudopotentials with small cutoff radii for the early transition metal elements Sc to Zn within the local density approximation of density functional theory. The pseudopotentials have been directly tested for accuracy within QMC by calculating the first through fourth ionization potentials of the isolated transition metal (M) atoms and the binding curve of each M-O dimer. We find the ionization potentials to be accurate to 0.16(1) eV, on average, relative to experiment. The equilibrium bond lengths of the dimers are within 0.5(1)% of experimental values, on average, and the binding energies are also typically accurate to 0.18(3) eV. The level of accuracy we find for atoms and dimers is comparable to what has recently been observed for bulk metals and oxides using the same pseudpotentials. Our QMC pseudopotential results also compare well with the findings of previous QMC studies and benchmark quantum chemical calculations.PACS numbers: 71.15.Dx, 71.15.Nc Transition metal oxides are an essential class of materials for energy applications. These materials find applications as diverse as catalysis, energy storage, and superconductivity. The ability to tailor the electronic functionality of transition metal oxides is clearly bolstered by continuing to develop a detailed theoretical understanding of these materials. Unfortunately it is this same class of materials that presents some of the greatest resistance to detailed theoretical characterization. Part of this challenge directly relates to the more localized electrons occupying the partially filled d states of the transition metal cations, leading to strong electron-electron interactions. Early characterizations of transition metal oxides by band theory incorrectly predicted many of them to be metals 1 . This departure from the expectations of band theory has lead to the widespread acceptance of strong electron correlation in these materials, in essence meaning that the Coulomb repulsion among electrons needs to be taken into account with some care. Continuum quantum Monte Carlo (QMC) methods 2 have the potential to address this need, as they are capable of taking the many body correlations of interacting electrons explicitly into account with few fundamental approximations. Though the application of such methods generally comes at a high computational cost, with the dramatic increase in available computing power seen in recent years these methods are now being brought to bear 3-9 on this challenging class of materials.One of the most prominent approximations involved in the practical application of quantum Monte Carlo techniques is the use of pseudopotentials to remove the high-energy core electrons. The fundamental idea behind pseudopotentials is that they preserve the electronic characteri...

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“…In principle, quasiparticle calculations provide a more accurate description, 33,34 but these are computationally intensive and are based on geometries that are obtained with DFT. 35,36 Quantum Monte Carlo calculations [37][38][39] can also provide a direct solution to the many-body problem, but applications to defects have been limited due to the computational complexity.…”

Section: Introductionmentioning

confidence: 99%

Computationally predicted energies and properties of defects in GaN

2017

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Recent developments in theoretical techniques have significantly improved the predictive power of density-functional-based calculations. In this review, we discuss how such advancements have enabled improved understanding of native point defects in GaN. We review the methodologies for the calculation of point defects, and discuss how techniques for overcoming the band-gap problem of density functional theory affect native defect calculations. In particular, we examine to what extent calculations performed with semilocal functionals (such as the generalized gradient approximation), combined with correction schemes, can produce accurate results. The properties of vacancy, interstitial, and antisite defects in GaN are described, as well as their interaction with common impurities. We also connect the first-principles results to experimental observations, and discuss how native defects and their complexes impact the performance of nitride devices. Overall, we find that lower-cost functionals, such as the generalized gradient approximation, combined with band-edge correction schemes can produce results that are qualitatively correct. However, important physics may be missed in some important cases, particularly for optical transitions and when carrier localization occurs.

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Structural stability and defect energetics of ZnO from diffusion quantum Monte Carlo

Cited by 58 publications

References 118 publications

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

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

Pseudopotentials for quantum Monte Carlo studies of transition metal oxides

Computationally predicted energies and properties of defects in GaN

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