Seminarium Oddziału Badań Magnetyków
sala nr 6 (bud. II)
How to use the DFT method to describe correlated electron systems using a magnetic nanomolecule as an example
prof. dr hab. Romuald Lemański
Oddział Teorii Materii Skondensowanej INTiBS PAN we Wrocławiu
Streszczenie:
It is well known that ab initio methods based on DFT are very useful in solid state physics. However, in many cases they do not correctly describe the phenomena caused by electron correlations. On the other hand, there are theories that specialize in describing systems of correlated electrons. With this in mind we will show, using the example of a magnetic nanomolecule, how the joint application of both approaches leads to a correct description of correlated electron systems.
More specifically, we will present a microscopic description of molecular magnets by the multiorbital Hubbard model. The parameters of the Hamiltonian were taken from ab initio calculations performed using the DFT method by other authors. In the limit of large Coulomb on-site interaction, we derived the spin Hamiltonian using the perturbation theory. We determined the magnetic coupling constant between two ions in two different ways: (a) from the expression obtained in the perturbation calculus and (b) from the analysis of distances between the lowest levels of the energy spectrum obtained by diagonalization of the multiorbital Hubbard model. The procedure we use can be applied to various nanomagnets, but we performed the final calculations for the molecular ring Cr8. One of our conclusions is that the correlated hopping (the dependence of the electron hopping amplitude between orbitals on the degree of their occupancy) can reduce the antiferromagnetic exchange between ions, which is essential for a proper description of Cr8.
The main part of the presented material was published in the paper: J. Matysiak and R. Lemański, Phys. Rev. B 104, 014431 (2021).
