Thesis (MSc. (Physics)) --University of Limpopo, 2009 / Calculations were carried out on transition-metal sulphides (TMS) and transitionmetal
arsenides (TMA), in both pyrite- and marcasite-type structures, using planewave
(PW) pseudopotential methods within density functional theory (DFT) in the local density approximation (LDA). The structural, electronic and optical properties for both pyrite- and marcasite-type structures (naturally occurring and converted)
have been investigated. The equilibrium lattice parameters were investigated and are
in good agreement with the experimental values. The heats of formation calculations
predict that the naturally occurring pyrite- and marcasite-type structures are more
stable than the converted ones. In particular, the calculated pyrite-type RuS2 compares well to the experimental value (with energy difference of 0.381 eV/atom). The bulk modulus and elastic properties were calculated. The predicted anisotropic ratio shows that the naturally occurring pyrite- and marcasite-type structures are more stable than the converted ones.
Moreover, the electronic density of states and band structure calculations reveal that
most compositions shows semiconducting behaviour except for the converted pyritetype
structures, i.e OsAs2 and RuAs2 where a metallic behaviour was observed. The
electronic charge density and charge density difference show charge accumulation on
bonding atoms, predicting the charge gain/ loss and nature of bonding to be covalent/
weak ionic between the atoms.
Lastly, optical properties are computed at equilibrium and predict that naturally
occurring structures have lower absorption and reflectivity than the converted
structures. At different pressures ranging from -10 GPa to 10 GPa, the absorption and
reflectivity spectra show a shift from the 0 GPa spectrum for all the structures / National Research Foundation
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/574 |
| Date | January 2009 |
| Creators | Rapetsoa, Mamphule Johannes |
| Contributors | Ngoepe, P.E., Chauke, H.R. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | x, 90 leaves : ill. |
| Relation |
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