arXiv subjects

Malgorzata Wierzbowska

Publications and source records attributed to Malgorzata Wierzbowska.

21 records · Page 2Linked to original sources

arXiv2005

Effect of electron correlations in Pd, Ni, and Co monowires

We investigated the effect of mean-field electron correlations on the band electronic structure of Co, Ni, and Pd ultra-thin monatomic nanowires, at the breaking point, by means of density-functional calculations in the self-interaction corrected LDA approach (LDA+SIC) and alternatively by the LDA+$U$ scheme. We find that adding static electron correlations increases the magnetic moment in Pd monowires, but has negligible effect on the magnetic moment in Co and Ni. Furthermore, the number of $d$-dominated conductance channels decreases somewhat compared to the LDA value, but the number of $s$-dominated channels is unaffected, and remains equal to one per spin.

cond-mat.mtrl-sci↗

arXiv2004

Different origin of the ferromagnetic order in (Ga,Mn)As and (Ga,Mn)N

The mechanism for the ferromagnetic order of (Ga,Mn)As and (Ga,Mn)N is extensively studied over a vast range of Mn concentrations. We calculate the electronic structures of these materials using density functional theory in both the local spin density approximation and the LDA+U scheme, that we have now implemented in the code SIESTA. For (Ga,Mn)As, the LDA+U approach leads to a hole mediated picture of the ferromagnetism, with an exchange constant $Nβ$ =~ -2.8 eV. This is smaller than that obtained with LSDA, which overestimates the exchange coupling between Mn ions and the As $p$ holes. In contrast, the ferromagnetism in wurtzite (Ga,Mn)N is caused by the double-exchange mechanism, since a hole of strong $d$ character is found at the Fermi level in both the LSDA and the LDA+U approaches. In this case the coupling between the Mn ions decays rapidly with the Mn-Mn separation. This suggests a two phases picture of the ferromagnetic order in (Ga,Mn)N, with a robust ferromagnetic phase at large Mn concentration coexisting with a diluted weak ferromagnetic phase.

cond-mat.mtrl-sci↗

arXiv2004

Multiplet Structures of Charged Fullerenes

We calculated multiplet splittings for positively and negatively charged fullerene ions within the CAS SCF method, and extracted model parameters for the intramolecular Hamiltonian. The method treats correctly the symmetry of ground and excited states for partially occupied degenerate molecular orbitals. We compare our results to previous calculations by the LDA, MNDO and model SCF methods. The multiplet averaged Coulomb parameter U is about 3.1 eV for electrons and 3.2 eV for holes. The Hund's rule exchange parameter J is found to be 113 meV for electrons and 192 meV for holes.

cond-mat.str-el↗