Localised Wannier orbital basis for the Mott insulators GaV4S8 and GaTa4Se8

CAMJAYI, ALBERTO; RUBEN WEHT; M. J. ROZENBERG

EUROPHYSICS LETTERS

EPL ASSOCIATION

Lugar: Bristol; Año: 2012 vol. 100 p. 70041 - 70045

0295-5075

We study the electronic properties of GaV4S8 (GVS) and GaTa4Se8 (GTS), two distant members within the large family of chalcogenides AM4X8, with A = {Ga, Ge}, M = {V, Nb, Ta, Mo} and X = {S, Se}. While all these compounds are Mott insulators, their ground states show many types of magnetic order, with GVS being ferromagnetic and GTS non-magnetic. Based on their band structures, calculated with density functional theory methods, we compute an effective tight-binding Hamiltonian in a localised Wannier basis set, for each of the two compounds. The localised orbitals provide a very accurate representation of the band structure, with hopping amplitudes that rapidly decrease with distance. We estimate the superexchange interactions and show that the Coulomb repulsion with Hund´s coupling may account the for the different ground states observed in GVS and GTS. Our localised Wannier basis provides a starting point for realistic dynamical mean-field theory studies of strong-correlation effects in this family compounds.