Hole localization in [AlO4] defects in silica materials

Abstract

First-principles calculations based on cluster models have been performed to investigate the ground state and the optically excited states of the [AlO(4)](0) hole in alpha-quartz and in the siliceous zeolite ZSM-5. The structure and spectroscopic properties of this defect have been studied using the recently developed Becke88-Becke95 one-parameter model for kinetics (BB1K) functional of Zhao et al., [J. Phys. Chem. A 108, 2715 (2004)]. Our results show that the BB1K method is significantly more reliable and more accurate than the standard density-functional theory (DFT) functionals at reproducing the localized spin density on one oxygen atom and the hyperfine coupling constants associated with the hole. Furthermore, we find that the BB1K results are in close agreement with experiments, and with the self-interaction-free unrestricted Hartree-Fock (UHF) and unrestricted second-order Møller-Plesset perturbation theory (UMP2) calculations. For the first time, we present results of the ground-state paramagnetic properties of the Al defect in ZSM-5. Similar to the theoretical work for defective alpha-quartz, we find that the BB1K, UHF, UHFLee-Yang-Parr, and UMP2 calculations show a localized hole on one oxygen neighboring the Al, while even the best to date thermochemically derived hybrid generalized gradient approximation density-functional, B97-2, predicts a different model where the hole is distributed over two oxygen. We have further considered the optical transitions of the [AlO(4)](0) center in alpha-quartz and ZSM-5. In both systems, our BB1K time-dependent density-functional theory (TDDFT) and configuration interaction singles (CIS) calculations predict that the most likely transition involves electron transfer from the hole-bearing oxygen to other neighboring oxygen ions. This reinforces the experimental conclusions obtained for defective alpha-quartz. Notably, the two lowest, most dominant excitation energies calculated by BB1K-TDDFT (1.99 and 3.03 eV) show excellent agreement with experiment (1.96 and 2.85 eV [B. K. Meyer, J.M. Spaeth, and J.A. Weil, J. Phys. C: Solid State Phys. 17, L31 (1987)]) clearly outperforming the CIS method and other DFT calculations available in the literature.

Hybrid functional calculations of the Al impurity inαquartz: Hole localization and electron paramagnetic resonance parameters

“…This defect is believed to cause the smoky coloration of quartz crystals 2,7 . On theoretical level, this 'classical' model has been confirmed by cluster calculations on unrestricted Hartree-Fock or hybrid functional level [8][9][10][11] , yielding a polaronic hole localization and hyperfine coupling constants with 27 Al, 17 O and 29 Si in good agreement with experiments. It was shown that the defect undergoes local symmetry breaking and Jahn-Teller reconstruction with one oxygen atom relaxing away from the Al ion.…”

“…Correspondingly, the Al-O bond lengths in this case are very similar. On the other hand, To et al 11 found a bond elongation of 12% using the BB1K functional (42% HF exchange), whereas Pacchioni et al 10 reported a 14% elongation from their 100% Hartree-Fock calculations. Our cluster calculations using the BHandHLYP hybrid functional (50% exact exchange) yield spin localization and defect geometry very similar to our sX-LDA results.…”

Communication: Hole localization in Al-doped quartz SiO2 within ab initio hybrid-functional DFT

“…21 For instance, To et al found that a semi-empirical hybrid functional including 42% of EXX (called BB1K functional) yields the correct picture. 22 In view of the preceding work, it may be concluded that some amount of empiricism is required to tackle the Alimpurity problem within DFT, casting doubts on its actual predictive power. Recently, a rationale for the value that the EXX fraction takes in extended systems has been put forward.…”

Polaronic hole localization and multiple hole binding of acceptors in oxide wide-gap semiconductors

“…A number of electronic structure methods are able to restore the qualitative picture of single-site localization, e.g., self-interaction correction (SIC) [4,5], DFT+U [6,9], and hybrid-DFT [10,11].…”