“…Marcasite intermetallic FeSb 2 features several properties of interest. These include a small semiconducting gap, excellent electrochemical performance in Na-ion batteries, metallic surface states of possible topological origin, and large values of thermopower whose mechanism of enhancement is relevant for future solid state cryodevices. − A large body of experimental and theoretical results point to interplay of crystal lattice effects with electron–electron correlations within the spin fluctuations, Hubbard approach, valence, or spin-state transitions. ,,,− The energy gap is driven by inter-Fe hybridization of states with different orbital characteran orbitally selective Kondo-semiconductor-like state. , On the other hand, electron correlations influence energy gap, localization of conduction states, charge transfer, and bond length between metal and ligand atomic sites, all of which are important in high energy density battery materials. − …”