Titanium nitride: A correlated metal at the threshold of a Mott transition

We investigate electron correlation effects in stoichiometric titanium nitride (TiN) using a combination of electronic structure and many-body calculations. In a first step, the Nth-order muffin-tin-orbital technique is used to obtain parameters for the low-energy Hamiltonian in the Ti-d(t(2g))-band manifold. The Coulomb interaction U and Hund's rule exchange parameter J are estimated using a constrained local-density-approximation calculation. Finally, the many-body problem is solved within the framework of the variational cluster approach. Comparison of our calculations with different spectroscopy results stresses the importance of electronic correlation in this material. In particular, our results naturally explain a suppression of the TiN density of states at the Fermi level (pseudogap) in terms of the proximity to a Mott-metal-insulator transition.