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Density-functional calculation of the electronic structure and equilibrium geometry of iron pyrite ( FeS 2 )

1994; American Physical Society; Volume: 50; Issue: 12 Linguagem: Inglês

10.1103/physrevb.50.8214

1095-3795

Ying Zeng, N. A. W. Holzwarth,

Minerals Flotation and Separation Techniques

The electronic structure and equilibrium geometry of the pyrite form of ${\mathrm{FeS}}_{2}$ was studied using self-consistent density-functional theory comparing the local-density-approximation (LDA) and the generalized-gradient-approximation (GGA) forms of the exchange-correlation functional. The calculated contour map of the electron-deformation density is consistent with analysis of high-resolution x-ray-diffraction data, showing excess charge in nonbonding d states on the Fe sites. At the experimentally measured geometry, the cohesive energy is calculated to be 16.7 eV/${\mathrm{FeS}}_{2}$ and 9.4 eV/${\mathrm{FeS}}_{2}$ for the LDA and GGA forms, respectively; the GGA result comparing well with the experimental value of 10.7 eV/${\mathrm{FeS}}_{2}$. Optimizing the cohesive energy as a function of geometry, both the LDA and GGA calculations find the optimal structure to be expanded relative to the experimental geometry with the lattice constant expanded by 1% and the S-S bond length expanded by 6%, corresponding to a 0.1-eV increase in the cohesive energy for each ${\mathrm{FeS}}_{2}$ unit. Similar results were obtained for ${\mathrm{RuS}}_{2}$.