The Electronic Pseudo Band Gap States And Electronic Transport Of The Full-Heusler Compound Fe2val

For Fe2VAl the temperature-dependent Seebeck coefficient S(T) and electrical resistivity rho(T) were calculated within the framework of density functional theory (DFT). The DFT calculations were extended in terms of a DFT/LDA+U approach with U - J values attributed to Fe-d-like states. For simulating the general features of the measured data, a large range of U - J values was scanned with U - J = 2.145 eV as the recommended value. For this value a very small negative indirect gap of E(X) - E(Gamma) = -0.0093 eV is found, which is significantly reduced as compared to the DFT-GGA value of -0.164 eV. Charge transfer was derived by Bader's approach, resulting in a significant transfer of 0.75 electronic charges to each Fe atom from Al (1.03) and V (0.48). The pseudogap states around the Fermi energy were analyzed in detail in terms of density of states, band structures and charge density contours. These states almost exclusively govern S(T) and rho(T). They have large dispersions and are centered at Gamma and X. They consist of tails of localized V and Fe states dangling to the Al site. The dispersion of the band along the k space direction X-Gamma was modelled in terms of a tight-binding ansatz, resulting in k-dependent matrix elements. From our DFT study, based on the findings for S(T) and rho(T), it appears that Fe2VAl has a very small negative indirect gap in the electronic structure. By fitting the temperature-dependent Seebeck coefficient within a parabolic band model, a tiny positive band gap of around 0.003 eV is revealed which qualitatively agrees with the DFT results.