Ab initio modelling of transition metals in diamond

Watkins, Matthew and Mainwood, A. (2003) Ab initio modelling of transition metals in diamond. Journal of Physics: Condensed Matter, 15 (39). S2913-S2927. ISSN 0953-8984

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Item Type:Article
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Transition metals (TM) from the first transition series are commonly used as solvent catalysts in the synthesis of diamond by high pressure, high temperature processes. Ab initio calculations on these metals, in finite clusters of tetrahedrally coordinated carbon, enable us to investigate trends in their stability and properties. By carrying out systematic studies of interstitial, substitutional and semi-vacancy TM defects, we show that the electronic structure of the TMs is complicated by the presence of 'dangling bonds' when the TM disrupts the crystal lattice: interstitial defects conform to the Ludwig - Woodbury (LW) model, whilst substitutional and semi-vacancy defects move from approximating the LW model early in the transition series to approaching the vacancy model for the heavier metals. Multi-configurational self-consistent field methods allow genuine many-electron states to be modelled; for neutral interstitial, and all substitutional TMs, the crystal fields are found to exceed the exchange energies in strength. Consequently, low spin states are found for these defects. We find substitutional defects to be the most stable, but that semi-vacancy TMs are very similar in energy to the substitutional defects late in the transition series; interstitial defects are only metastable in diamond. Given appropriate charge compensators neutral and positively charged interstitial TM defects were stable, while negatively charged species appeared to be strongly disfavoured.

Keywords:Catalysts, Crystal defects, Crystal lattices, Electronic structure, High temperature effects, Mathematical models, Solvents, Substitution reactions, Synthesis (chemical), Synthetic diamonds, Interstitial defects, Ludwig-Woodbury model, Semi vacancy defects, Transition metals
Subjects:F Physical Sciences > F200 Materials Science
F Physical Sciences > F300 Physics
Divisions:College of Science > School of Mathematics and Physics
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ID Code:17726
Deposited On:12 Aug 2015 15:51

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