Structure determination of the AlO4 hole centres in α-quartz by EPR and SCF MO

We report the theoretical prediction of single and paired electron self-trapping in Ge(2)Se(3). In finite atomic cluster, density functional calculations, we show that excess single electrons in Ge(2)Se(3) are strongly localized around single germanium dimers. We also find that two electrons prefer to trap around the same germanium dimer, rupturing a neighboring Ge-Se bond. Localization is less robust in periodic, density functional calculations. While paired electron self-trapping is present, as shown by wavefunction localization around a distorted Ge-Ge dimer, single-electron trapping is not. This discrepancy appears to depend only on the boundary conditions and not on the exchange-correlation potential or basis set. For single- and paired-electron trapping, we report the adiabatic barriers to motion and we estimate hopping rates and freeze-in temperatures. For the single trapped electron, we also predict the (73)Ge and (77)Se hyperfine coupling constants.

Section: Discussionmentioning

confidence: 99%

Self-trapping of single and paired electrons in Ge₂Se₃

Edwards

Campbell

Pineda

2012

“…y,z =x,y,z m=x,y,z n=x,y,z × p=x,y,z r=x,y,z g j, mnpr B j S S m S n S p S r . (11) At first sight each of equations ( 10) and ( 11) appears a more compact way of expressing the SH for such terms but both are reducible. In equations (10), for example, 21 B S 3 terms reduce to 14 and 33 B S 5 terms reduce to 22, i.e., 7 and 11 redundancy equations respectively are required.…”

Section: Extension To Cartesian Tensors Of Ranks 4 Andmentioning

confidence: 99%

“…(11) At first sight each of equations ( 10) and ( 11) appears a more compact way of expressing the SH for such terms but both are reducible. In equations (10), for example, 21 B S 3 terms reduce to 14 and 33 B S 5 terms reduce to 22, i.e., 7 and 11 redundancy equations respectively are required. These are results that we have stated earlier [1,2], and shall return Table 2.…”

Section: Extension To Cartesian Tensors Of Ranks 4 Andmentioning

confidence: 99%

“…Secondly, as addressed in a recent paper [9], is it valid to frame a SH in, for example, a combination of Cartesian (for g, A, D, P and g n ), Stevens' (for ZFS terms J 2(J = S, I )) and TSTO forms? This is an option for example in the international programme EPR-NMR [10,11] on the grounds that the Cartesian and Stevens' forms are most familiar to would-be users-but, is the SH thus framed valid when high-spin terms of the type described above are present? This is a particular question raised in [9].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Higher-order Zeeman and spin terms in the electron paramagnetic resonance spin Hamiltonian; their description in irreducible form using Cartesian, tesseral spherical tensor and Stevens’ operator expressions

McGavin¹,

Tennant²

2009

In setting up a spin Hamiltonian (SH) to study high-spin Zeeman and high-spin nuclear and/or electronic interactions in electron paramagnetic resonance (EPR) experiments, it is argued that a maximally reduced SH (MRSH) framed in tesseral combinations of spherical tensor operators is necessary. Then, the SH contains only those terms that are necessary and sufficient to describe the particular spin system. The paper proceeds then to obtain interrelationships between the parameters of the MRSH and those of alternative SHs expressed in Cartesian tensor and Stevens operator-equivalent forms. The examples taken, initially, are those of Cartesian and Stevens' expressions for high-spin Zeeman terms of dimension BS(3) and BS(5). Starting from the well-known decomposition of the general Cartesian tensor of second rank to three irreducible tensors of ranks 0, 1 and 2, the decomposition of Cartesian tensors of ranks 4 and 6 are treated similarly. Next, following a generalization of the tesseral spherical tensor equations, the interrelationships amongst the parameters of the three kinds of expressions, as derived from equivalent SHs, are determined and detailed tables, including all redundancy equations, set out. In each of these cases the lowest symmetry, [Formula: see text] Laue class, is assumed and then examples of relationships for specific higher symmetries derived therefrom. The validity of a spin Hamiltonian containing mixtures of terms from the three expressions is considered in some detail for several specific symmetries, including again the lowest symmetry. Finally, we address the application of some of the relationships derived here to seldom-observed low-symmetry effects in EPR spectra, when high-spin electronic and nuclear interactions are present.

“…Rather than fix the g n matrix as the 3 × 3 unit matrix multiplied by an isotropic value for an assumed nucleus, it was constrained to be isotropic and fitted along with the elements of all the other parameter matrices using the programme EPR-NMR [7]. As shown in table 1, the final fitting was very precise with a root-mean-squared deviation (RMSD) of only 0.003 mT, being one-tenth of the average peak-to-peak linewidth of 0.03 mT.…”

Section: Fittingmentioning

confidence: 99%

15 K EPR of an oxygen-hole boron centre, [BO₄]⁰, in x-irradiated zircon

Walsby

Lees

Tennant

et al. 2000

Precise interaction matrices are reported for a boron-stabilized oxygenic-hole centre in x-irradiated zircon as derived from x-band electron paramagnetic resonance (EPR) measurements at ca 15 K. The presence of boron has been identified unequivocally through the observation and spin Hamiltonian analysis of superhyperfine structures from both naturally occurring isotopes of boron. Each of the parameter matrices indicates that the centre has point-group symmetry m (Cs ), as is common in hole centres in zircon, where the hole centre is trapped on an oxygen atom within one of the crystal mirror planes. Analysis of the principal directions of these matrices indicates that the boron atom resides in a silicon position neighbouring the oxygenic electron vacancy.