Modeling charge self-trapping in wide-gap dielectrics: Localization problem in local density functionals

Gavartin, J. L.; Sushko, Peter V.; Shluger, Alexander L.

doi:10.1103/physrevb.67.035108

Cited by 98 publications

(89 citation statements)

References 53 publications

(81 reference statements)

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“…51 In this work we used the nonlocal functional HSE and obtained the electron localization in Ge in Li electron centers in α-quartz. The hyperfine splitting constants and g-tensor components calculated for the Li center in quartz are in good agreement with the experimental values suggesting that HSE can predict the electronic structure of electron traps in silica relatively accurately.…”

Section: Discussionmentioning

confidence: 99%

Nature of intrinsic and extrinsic electron trapping in SiO2

et al. 2014

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Using ab initio calculations we demonstrate that extra electrons in pure amorphous SiO2 can be trapped in deep band gap states. Classical potentials were used to generate amorphous silica models and density functional theory to characterize the geometrical and electronic structures of trapped electrons. Extra electrons can trap spontaneously on pre-existing structural precursors in amorphous SiO2 and produce ≈ 3.2 eV deep states in the band gap. These precursors comprise wide (≥132 • ) O-Si-O angles and elongated Si-O bonds at the tails of corresponding distributions. The electron trapping in amorphous silica structure results in an opening of the O-Si-O angle (up to almost 180 • ). We estimate the concentration of these electron trapping sites to be ≈ 4 × 10 19 cm −3 . The structure of these centers is similar to that of Ge and Li electron centers in α-quartz.

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Section: Discussionmentioning

confidence: 99%

Nature of intrinsic and extrinsic electron trapping in SiO2

et al. 2014

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“…[11]), the self-trapping of hole centres and their trapping at defects (see, e.g., Ref. [12]), and the conflict between theory and experiment for the slope, dT /dp, of their melting curves [13,14,15,16]. Beyond this, we hope that the experience gained here will help to prepare the way for the application of QMC to transition-metal oxides such FeO, where electron correlation is highly non-trivial.…”

Section: Introductionmentioning

confidence: 99%

Quantum Monte Carlo calculations of the structural properties and the B1-B2 phase transition of MgO

et al. 2005

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We report diffusion Monte Carlo (DMC) calculations on MgO in the rock-salt and CsCl structures. The calculations are based on Hartree-Fock pseudopotentials, with the single-particle orbitals entering the correlated wave function being represented by a systematically convergeable cubic-spline basis. Systematic tests are presented on system-size errors using periodically repeating cells of up to over 600 atoms. The equilibrium lattice parameter of the rock-salt structure obtained within DMC is almost identical to the Hartree-Fock result, which is close to the experimental value. The DMC result for the bulk modulus is also in good agreement with the experimental value. The B1-B2 transition pressure (between the rock-salt and CsCl structures) is predicted to be just below 600 GPa, which is beyond the experimentally accessible range, in accord with other predictions based on Hartree-Fock and density functional theories.

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“…61 Note that LDA and GGA calculations typically fail to describe the localized 3d and 4f states and the charge localization in self-trapped electrons, holes, and excitons due to the self-interaction error. [62][63][64] The minimization of the artificial self-interaction often leads to artificial over-delocalization of orbitals. On the other hand, the Hartree-Fock (HF) calculations with exact exchange but no correlation usually overestimate the localization.…”

Section: 57mentioning

confidence: 99%

Using DFT Methods to Study Activators in Optical Materials

2015

ECS J. Solid State Sci. Technol.

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Density functional theory (DFT) calculations of various activators (ranging from transition metal ions, rare-earth ions, ns 2 ions, to self-trapped and dopant-bound excitons) in phosphors and scintillators are reviewed. As a single-particle ground-state theory, DFT calculations cannot reproduce the experimentally observed optical spectra, which involve transitions between multi-electronic states. However, DFT calculations can generally provide sufficiently accurate structural relaxation and distinguish different hybridization strengths between an activator and its ligands in different host compounds. This is important because the activator-ligand interaction often governs the trends in luminescence properties in phosphors and scintillators, which can be used to search for new materials. DFT calculations of the electronic structure of the host compound and the positions of the activator levels relative to the host band edges in scintillators are also important for finding optimal host-activator combinations for high light yields and fast scintillation response. Mn 4+ Luminescence of materials when excited by photons or ionizing radiation is the foundation for numerous technologies, such as energy efficient lighting (fluorescent lamps and white LEDs), laser, medical imaging, and nuclear materials detection.1-3 Efficient luminescence in semiconductors and insulators usually relies on the localization of excited electrons and holes at certain impurities, which act as luminescence centers (or activators). An activator can trap electrons and holes for efficient radiative recombination and is the essential component of a phosphor or scintillator material. The commonly used activators are typically multivalent ions, which can insert multiple electronic states inside the bandgap of the host material. 45 Good examples of the multivalent ions that can act as luminescent centers are rare-earth ions (e.g., Ce 3+ , Eu 2+ ), 6-11 transition metal ions (e.g., Cr 3+ , Mn 4+ ), [12][13][14][15][16][17] and ns 2 ions (ions with outer electron configuration of ns 2 , such as Tl + , Sn 2+ ). 18-20Energy efficiency is critically important for phosphors used for lighting. To suppress the energy loss through nonradiative recombination, a phosphor is excited by directly exciting activators, not the host (see Fig. 1a). The excitation energy is less than the bandgap energy of the host but is large enough to excite the activator. Since the excitation occurs locally at the activator, the chance for the excited activator to interact with nonradiative recombination centers, such as deep defects, is small. This is important for achieving high quantum efficiencies for phosphors. In scintillators used for detecting ionizing radiation, the radiation creates charge carriers in the valence and conduction bands of the host, which are subsequently trapped by activators, leading to radiative recombination (see Fig. 1b). In scintillators, a portion of the charge carriers need to travel a certain distance before being trapped by the activators, which ...

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Modeling charge self-trapping in wide-gap dielectrics: Localization problem in local density functionals

Cited by 98 publications

References 53 publications

Nature of intrinsic and extrinsic electron trapping in SiO2

Nature of intrinsic and extrinsic electron trapping in SiO2

Quantum Monte Carlo calculations of the structural properties and the B1-B2 phase transition of MgO

Using DFT Methods to Study Activators in Optical Materials

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