Structure and stability of the (001) alpha-quartz surface Article (Published Version) http://sro.sussex.ac.uk Goumans, T P M, Wander, Adrian, Brown, Wendy A and Catlow, C Richard A (2007) Structure and stability of the (001) alpha-quartz surface. Physical Chemistry Chemical Physics, 9 (17). 2146 -2152 . ISSN 1463 This version is available from Sussex Research Online: http://sro.sussex.ac.uk/48679/ This document is made available in accordance with publisher policies and may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the URL above for details on accessing the published version. Copyright and reuse:Sussex Research Online is a digital repository of the research output of the University.Copyright and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable, the material made available in SRO has been checked for eligibility before being made available.Copies of full text items generally can be reproduced, displayed or performed and given to third parties in any format or medium for personal research or study, educational, or not-for-profit purposes without prior permission or charge, provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way.Structure and stability of the (001) The structure and surface energies of the cleaved, reconstructed, and fully hydroxylated (001) a-quartz surface of various thicknesses are investigated with periodic density functional theory (DFT). The properties of the cleaved and hydroxylated surface are reproduced with a slab thickness of 18 atomic layers, while a thicker 27-layer slab is necessary for the reconstructed surface. The performance of the hybrid DFT functional B3LYP, using an atomic basis set, is compared with the generalised gradient approximation, PBE, employing plane waves. Both methodologies give similar structures and surface energies for the cleaved and reconstructed surfaces, which validates studying these surfaces with hybrid DFT. However, there is a slight difference between the PBE and B3LYP approach for the geometry of the hydrogen bonded network on the hydroxylated surface. The PBE adsorption energy of CO on a surface silanol site is in good agreement with experimental values, suggesting that this method is more accurate for hydrogen bonded structures than B3LYP. New hybrid functionals, however, yield improved weak interactions. Since these functionals also give superior activation energies, we recommend applying the new functionals to contemporary issues involving the silica surface and adsorbates on this surface.
We implemented and compared four algorithms to locate instantons, i.e., the most likely tunneling paths at a given temperature. These allow to calculate reaction rates, including atom tunneling, down to very low temperature. An instanton is a first-order saddle point of the Euclidean action in the space of closed Feynman paths. We compared the Newton-Raphson method to the partitioned rational function optimization (P-RFO) algorithm, the dimer method, and a newly proposed mode-following algorithm, where the unstable mode is directly estimated from the instanton path. We tested the algorithms on three chemical systems, each including a hydrogen transfer, at different temperatures. Overall, the Newton-Raphson turned out to be the most promising method, with our newly proposed mode following, being the fall-back option.
The (photo)physical properties of organometallic complexes are crucially affected by relativistic effects. In a non- or scalar-relativistic picture, triplet states are threefold degenerate. Spin-orbit coupling lifts this degeneracy (zero-field splitting, ZFS) and enables phosphorescence from the three triplet-like states to the ground state. The fine structure and radiative lifetimes of phosphorescent organometallic complexes are important properties for designing efficient organic light-emitting diodes (OLEDs). Here we show that experimental ZFSs and phosphorescent lifetimes for a large variety of organometallic complexes are well reproduced by self-consistent spin-orbit coupling TDDFT (SOC-TDDFT) calculations with a continuum solvation model. By comparing with perturbative SOC-TDDFT and gas phase calculations, we find that both full spin-orbit and solvation effects are important for the predicted properties. SOC-TDDFT is thus shown to be a useful predictive tool for the rational design of phosphors in OLEDs and other optoelectronic devices.
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