A.E. Antipov^{1}, A.I. Poteryaev^{2}, A.N.Rubtsov^{1}, and A.I. Lichtenstein^{3}

{1}: Moscow State University, Physics Department, Russia
{2}: Institute for physics of metals, Ekaterinburg, Russia
{3}: Hamburg University, Germany

Modern numerically-exact continuous-time Quantum Monte Carlo codes allow to study the electron correlations with very realistic models. Whose models are multiorbital and take into account the complete rotationally invariant matrix of the Coulomb interaction.. This allows us to include the effects of multiplet structure renormalization due to hybridization of atomic orbitals.

In this report, we present results of the weak-coupling continuous-time Quantum Monte Carlo simulations for several systems, in particular LiNiO2. LiNiO2 attracts a close attention, both for applied and fundamental physics. It is a cathode material for lithium-ion batteries and thus it has a clear technological importance. Being an insulator of Mott-Hubbard type with one electron in the Ni e_g^{sigma} band, this compound, surprisingly, has no any trace of the long-range magnetic and/or orbital ordering down to low temperatures (below 1 K). These puzzling properties cannot be correctly described by conventional band structure theory neither by LDA+U method. Our results reproduce the insulating behaviour of LiNiO2 and deliver a reasonable quantitative accuracy.