NiO and UPd2Al3 are considered as prototype compounds with very strong electron correlations, not well theoretically described so far. We have consistently described properties of NiO, reconciling its insulating ground state and a strong (antiferro-)magnetism with TN of 525 K. We calculated low-energy electronic structure associated with eight 3d strongly-correlated electrons at the Ni site in the incomplete 3d shell.
For intermetallic UPd2Al3 we have proved the existence of the strongly-correlated 5f3 configuration (U3+ ion). Our result is in agreement with inelastic-neutron-scattering experiment which reveals a low-energy structure below 20 meV.
From consistent description of basic properties of such different compounds as NiO and UPd2Al3 are I conclude that the strong correlations are mainly related with 1) the charge transfer during the formation of the compounds and with 2) the intra-atomic correlations responsible for the formation of the strongly-correlated atomic-like systems 3dn, 4fn or 5fn. For successful description the multipolar charge potentials, described customarily as the crystal field, and relativistic spin-orbit interactions are fundamentally important. According to the developed Quantum Atomistic Solid-State Theory (QUASST) I claim that the crystal-field interactions should be evaluated the first for any meaningful description of magnetic and electronic properties of any 3d/4f/5f compound. QUASST is supported by a recent EPR experiment on heavy-fermion metal YbRh2Si2 – the strongly-correlated 4f13 configuration has been found to exist at 1.5 K, i.e. at temperature being 15 times lower than the Kondo temperature.
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