Extended Huckel electronic calculations for PrFe 4 P 12
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Extended Huckel electronic calculations for PrFe4P 12 D. H. Galvan and J. C. Samaniego Reyna Centro de Ciencias de la Materia Condensada-UNAM, Apartado Postal 2681, CP 22800, Ensenada, B. C., México Abstract Electronic structure calculations were performed on PrFe 4P 12 filled skutterudite, in order to provide more information regarding its properties. The energy bands yielded information regarding the metallic behavior as well as a mini gap of 0.02 eV. Total and projected Density of States (DOS) yielded information for the existence of a hybridization between Pr -f, Fe -d and P -p orbitals. Hence, this compound could be considered a likely candidate as a thermoelectric compound. Introduction Filled skutterudites [1] are family of compounds with general formula RT4X12 (where R = alkaline earth, rare earth, actinide; T = Fe, Ru, Os; X = pnictogen: P, As, Sb) and crystallize [1,2] in the cubic skutterudite structure. These materials show a variety of interesting physical properties such as: superconductivity [3,4], magnetic order [5], small hybridization gap semiconductivity [6], valence fluctuation and heavy fermion behavior [7-8], non-Fermi liquid behavior [9] and metal-insulator transition [10]. Moreover, these compounds have attracted attention toward thermoelectric applications [11]. Computational details The electronic structure calculations reported in this study were performed using the tight-binding method [12] within the extended Huckel [13] framework using YAeHMOP [14] computer package including forbitals [15]. More details about the mathematical formulation of the method has been described elsewhere [16] and are omitted here for brevity. The structure for PrFe 4P 12 used through out the calculations is illustrated in Fig. 1, fro Leithe-Jasper et al. [17]. Large spheres represent Pr atoms, while medium size spheres represent Fe and smaller spheres depict P atoms. This material is characterized by the space group Im-3-Th 5 , No. 204 with primitive vector given by a = 0.771 nm. The Pr atoms are located in (2a), four Fe atoms at (8c) and 12 P atoms located at (24g). The atomic parameters employed in our calculations were provided by Alvarez et al. [18].
Figure 1 Unit cell for PrFe 4P 12. Large spheres represent Pr, medium size spheres correspond to Fe and small spheres are P atoms. Results and Discussion The band structure for PrFE4P 12 is depicted in Figures 2 (a) and (b), and were calculated using 51 k-points sampling the first Brillouin zone. The Fermi level is indicated by a horizontal dotted line. The inset in Fig. 2 depicts the Wigner-Seitz cell for a base center cubic configuration. The most important features in the dispersion diagrams for the filled skutterudite under study, is a tendency to form a pseudo gap that appears above the Fermi level (see Fig. 2 (b)), which is a typical characteristic of skutterudites, specially when a single band crosses the Fermi level, in this case a phosphorous p-band. This crossing band is pushed down by the repulsion with Pr f-resonance states. Fig. 2 (b) yie
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