Spectral and Magnetic Properties ofα- andγ-Ce from Dynamical Mean-Field Theory and Local Density Approximation

Abstract

We have calculated ground state properties and excitation spectra for Ce metal with the ab initio computational scheme combining local density approximation and dynamical mean-field theory (LDA+DMFT). We considered all electronic states, i.e. correlated f -states and non-correlated s-, p-and d-states. The strong local correlations (Coulomb interaction) among the f -states lead to typical many-body resonances in the partial f -density, such as lower and upper Hubbard band. Additionally the well known Kondo resonance is observed. The s-, p-and d-densities show small to mediate renormalization effects due to hybridization. We observe different Kondo temperatures for α-and γ-Ce (TK,α ≈ 1000 K and TK,γ ≈ 30 K), due to strong volume dependence of the effective hybridization strength for the localized f -electrons. Finally we compare our results with a variety of experimental data, i.e. from photoemission spectroscopy (PES), inverse photoemission spectroscopy (BIS), resonant inverse photoemission spectroscopy (RIPES) and magnetic susceptibility measurements.71.27.+a Strongly correlated electron systems , 74.25.Jb Electronic structure Ce metal is the simplest lanthanide compound with only one atom in a face centered cubic (fcc) crystal structure and a relatively small set of relevant electronic states derived from s-, p-d-and f -orbitals of Ce. It shows an unique isostructural (fcc to fcc) α → γ phase transition with increasing temperature. The high-temperature γ phase has 15% larger volume and displays a Curie-Weiss-like temperature dependence of the magnetic susceptibility signaling the existence of local magnetic moments while the α-phase has a Pauli-like temperature independent paramagnetism [1].While many different models were proposed to describe this system (for a review see [2]), the most relevant seems to be the periodic Anderson model. Studies based on the single impurity Anderson model [3] with a hybridization function obtained from LDA band structure calculations were rather successful in reproducing Kondo scales and spectra for α-and γ-Ce. However, an empirical renormalization of the hybridization function and position of the impurity level were needed for satisfactory agreement between calculated and experimental spectra.Due to the recent development of the Dynamical Mean-Field Theory [4] a more realistic treatment of Ce is now possible. In contrast to the Hubbard model (degenerate and non-degenerate), where hybridization occurs only between correlated d-or f -orbitals, Ce is much more complicated. The direct f -f hybridization is of the same order of magnitude as the hybridization of f -orbitals with the delocalized spd-states. Thus in order to describe Ce one even has to go beyond the periodic Anderson model, where only hybridization of the correlated f -orbitals with the delocalized states is included. In order to address this problem we used the most general procedure for calculating the Green function using a full basis set (s, p, d, f ) Hamiltonian with the integration over Brillouin zone in k-space....

Screening of4fmoments and delocalization in the compressed light rare earths

“…LDA+DMFT calculations 41,42,43,44,45,46 have consistently supported the KVC scenario 25,26,27,28 for Ce. They show, e.g., a rapid build up of the Kondo resonance for volume reduced across the γ-α two-phase region, which is taken as a signature of the onset of screening.…”

“…There have been experimental determinations of the Ce configuration weights w 0,1,2 using Anderson impurity model analyses of photoemission 27 and resonant inelastic x-ray scattering 22 data, and a number of LDA+DMFT calculations 41,42,43,44,46 of these quantities or related n f = 1−w 0 +w 2 . All are consistent with w 1 → 1, w k =1 → 0 in the large volume limit.…”

“…41,42,43,44,45,46 Such calculations for Ce also point to ongoing 4f delocalization in the relevant volume range, a critical driver of Mott transitions. 42,43 To further clarify the behavior of the compressed trivalent rare earths, the present paper reports LDA+DMFT calculations of the 4f spin and charge susceptibilities and the 4f n , 4f n±1 configuration weights for the first three members, Ce (n = 1), Pr (n = 2), and Nd (n = 3).…”

Theα→γTransition in Ce: A Theoretical View from Optical Spectroscopy

“…The expressions (4),(5) represent generalizations of the formulae for optical conductivity for a strongly correlated system, and involve the extra internal frequency integral appearing in Eq. (4).…”

“…The modern Dynamical Mean Field Theory (DMFT) modifies this simple single impurity picture by imposing a self-consistency condition on the bath that the f electrons experience. The full power of the DMFT method in combination with realistic band structure calculations (LDA+DMFT) [3] was recently brought to bear on this problem [4,5]. LDA+DMFT allowed the computation of the photoemission spectra of Cerium in both phases, and the thermodynamics of the transition starting from first principles.…”