arXiv subjects

Agnieszka L. Kozub

Publications and source records attributed to Agnieszka L. Kozub.

4 recordsLinked to original sources

arXiv2021

Polaronic Enhancement of Second-Harmonic Generation in Lithium Niobate

Density-functional theory within a Berry-phase formulation of the dynamical polarization is used to determine the second-order susceptibility $χ^{(2)}$ of lithium niobate (LiNbO$_3$). Defect trapped polarons and bipolarons are found to strongly enhance the nonlinear susceptibility of the material, in particular if localized at Nb$_\mathrm{V}$-V$_{\mathrm{Li}}$ defect pairs. This is essentially a consequence of the polaronic excitation resulting in relaxation-induced gap states. The occupation of these levels leads to strongly enhanced $χ^{(2)}$ coefficients and allows for the spatial and transient modification of the second-harmonic generation of macroscopic samples.

physics.optics↗

arXiv2016

Electronic structure and magnetism of samarium and neodymium adatoms on free-standing graphene

The electronic structure of selected rare-earth atoms adsorbed on a free-standing graphene was investigated using methods beyond the conventional density functional theory (DFT+U, DFT+HIA and DFT+ED). The influence of the electron correlations and the spin-orbit coupling on the magnetic properties has been examined. The DFT+U method predicts both atoms to carry local magnetic moments (spin and orbital) contrary to a nonmagnetic $f^6$ ($J=0$) ground-state configuration of Sm in the gas phase. Application of DFT${}+{}$Hubbard-I (HIA) and DFT${}+{}$exact diagonalization (ED) methods cures this problem, and yields a nonmagnetic ground state with six $f$ electrons and $J=0$ for the Sm adatom. Our calculations show that Nd adatom remains magnetic, with four localized $f$ electrons and $J=4.0$. These conclusions could be verified by STM and XAS experiments.

cond-mat.str-el↗

arXiv2016

Screening of magnetic moment at Co impurity in Cu host

Cobalt impurity located in the bulk copper is described making use of the multi-orbital Anderson impurity model that is parametrized to match the electronic structure from the local density approximation, and solved using the Lanczos method. We concentrate on the many-body description of the ground state and excitation spectra. The calculations yield a nonmagnetic ground state for the impurity atom. The computed spectral densities are in a good agreement with those obtained using the quantum Monte Carlo method.

cond-mat.str-el↗

arXiv2014

Theory of valence-band and core-level photoemission from plutonium dioxide

The correlated-band theory implemented as a combination of the local-density approximation with the dynamical mean-field theory is applied to PuO2. An insulating electronic structure, consistent with the experimental valence-band photoemission spectra, is obtained. The calculations yield a nonmagnetic ground state that is characterized by a noninteger filling of the plutonium 5f shell. The noninteger filling as well as the satellites appearing in the 4f core-level photoemission spectra originate in a sizable hybridization of the 5f shell with the 2p states of oxygen.

cond-mat.str-el↗