Time-dependent Local Spin-density Approximation Research Articles

Time-dependent local spin density approximation study of Luttinger liquids

We perform a time-dependent local spin density approximation (TDLSDA) study of one-dimensional Fermions with a contact interaction. We show that the simple TDLSDA approximation provides an exact description for density and spin density modes and conductance $G$ in one-dimensional quantum wires, by establishing a general equivalence between TDSLDA and Tomonaga-Luttinger model for the elementary excitation spectra in one-dimensional Fermi systems. The role of interaction effects is carefully analyzed especially in relation to the problem of the universality of the result $G=2{e}^{2}/h$ for the conductance of one-dimensional systems. Finally our results are in good agreement with the available experimental data on the one-dimensional plasmon dispersion, and conductance in GaAs quantum wires.

Effects of the exchange instability on collective spin and charge excitations of the two-dimensional electron gas

We report inelastic light scattering measurements of the elementary excitations of a two-dimensional (2D) electron gas formed in a modulation-doped GaAs single quantum well, when the first excited conduction subband begins to be populated and the sudden renormalization of its energy occurs due to an exchange-driven instability of the 2D system. The Hartree and exchange-correlation terms of the Coulomb interaction, which can be precisely determined from the energies of the charge and spin-density excitations in light scattering spectra, exhibit abrupt changes upon filling of the excited subband. Density-functional calculations of the collective excitations within the time-dependent local spin-density approximation provide a simple explanation for the strong enhancement of the Hartree term observed in the experiment. In contrast, the sudden reduction of exchange-correlation vertex corrections at the instability are not well accounted for by the theory. We discuss this discrepancy and present its peculiar temperature dependence.

Magneto-optics of three-dimensional quantum dots: a real time, time-dependent local spin–density approach

We perform adiabatic time-dependent local spin–density approximation (TDLSDA) calculations in real time of the excitation spectrum of three-dimensional quantum dots (QD's) in magnetic fields of arbitrary direction. In the case of parabolic confinement and electric dipole modes, the calculations reproduce exactly the generalized Kohn theorem, which is a stringent test of the numerical accuracy achieved by our practical implementation of TDLSDA. We apply the method to the study of spin dipole modes in a QD. Real time TDLSDA can be more efficient than Green's function methods to compute the dynamical properties of confined electrons, especially when the finite thickness of the system has to be taken into account. As an illustration, we obtain the dipole spin modes and the acoustic modes of vertical diatomic artificial quantum molecules at zero magnetic field.

Towards spectral pattern of spin polarized sodium clusters: The example of Na $\mathsf{_{12}}$

We investigate spin modes in the ground state and the polarized first isomer of the Na12 cluster describing the valence electrons in time-dependent local-spin-density approximation (TDLSDA) and the detailed ionic background using local pseudopotentials. The spin modes show a collective redshift compared to the unperturbed particle-hole excitations. They are strongly fragmented and the average energy of the modes along the principal axes are related to the underlying geometry (triaxial or axially symmetric). For the polarized isomer, we find significant cross talk between the spin modes and the dipole plasmon, which hints at a possible spectroscopic identification.

Magnetic dichroism at the giant dipole resonance of Fe and Mn via time-dependent density-functional theory

The polarization-resolved photoabsorption cross section has been calculated in the vicinity of the giant dipole resonances of Fe (45-65 eV) and Mn (45-60 eV) using the relativistic time-dependent local spin-density approximation. The method accounts for the largest features in the unpolarized experimental total cross sections, after Gaussian broadening is applied; however, minor features are not given correctly. Both circular and linear dichroic spectra are presented, however experimental data are not yet available.

Sum Rules for the spin surface response of metal clusters within the time dependent local spin density approximation

We study surface spin collective modes of simple metallic clusters using a sum rule approach. We derive analytical expressions for the energy and cubic energy-weighted moments of the time-dependent local-spin-density approximation (TDLSDA) strength function. With these two moments we obtain a mean excitation energy of multipole spin modes and study its dispersion with cluster size up to very large sizes. The crucial roles played by the surface diffuseness and by correlation and kinetic energy effects on the resonance energies are stressed.

Density-functional theory with optimized effective potential and self-interaction correction for ground states and autoionizing resonances

We present a self-interaction-free density-functional theory (DFT) for the treatment of both the static properties of the ground states and the photoionization processes of many-electron systems. The method is based on the Krieger-Li-Iafrate (KLI) treatment of the optimized effective potential (OEP) theory and the incorporation of an explicit self-interaction correction (SIC) term. Such an extended OEP--KLI-SIC method uses only orbital-independent single-particle local potentials and is thus computationally more efficient and yet maintains good accuracy. The usefulness of the procedure is examined by the studies of the static properties of the ground states of atoms (Z\ensuremath{\leqslant}18) and the dynamical photoionization processes involving autoionizing resonances. Both the energy functionals of the local spin-density approximation (LSDA) and Becke's exchange energy functional and the correlation energy functional of Lee-Yang-Parr (BLYP) are used as the input to the KLI-SIC calculations. It is found that the implementation of the KLI-SIC procedure gives rise to optimized effective potentials that possess the correct behavior in both short-range and long-range regimes. As a consequence, the LSDA and BLYP ionization potentials are significantly improved. For higher-Z atoms, the improvement of the LSDA total energies and the ionization potentials are particularly remarkable, approaching the experimental or exact values. As another test of the KLI-SIC method, we have performed the calculation of the photoionization cross sections of the Ne atom using both the time-independent and time-dependent LSDA (TDLSDA) methods. We found that the TDLSDA results agree closely with the experimental data in the broad peak region, followed by a series of sharp resonances due to the 2s\ensuremath{\rightarrow}np resonant transitions. The calculated linewidths and resonance line profile parameters are in reasonable agreement with both the experimental and the configuration-interaction (R-matrix) results, demonstrating the usefulness of the KLI-SIC procedure for achieving accurate DFT calculations in both static properties and dynamical processes.

Calculation of the photoionization cross sections for the potassium and the bromine atoms by using the time-dependent local spin density approximation

The density functional approach to local field is extended to a spin-polarized finite electronic system. The time-varying local field, which is dependent on the spin components of electrons, incorporates the polarization-type many-body effects of electronic correlations into the photoionization cross section. To examine the spin-dependent local field effects, the photoionization cross sections of the potassium and the bromine atom are calculated by using this time-dependent local spin density approximation. The results obtained are compared with available information from other theoretical methods and experiments.

Photoabsorption of Fe, Co, and Ni atoms embedded in Al-clusters near 3p-ionization threshold of impurity

Photoionization cross sections of Fe, Co, and Ni atoms inside Al jellium-clusters (containing up to 90 atoms) in the energy range near the 3p ionization threshold of the impurity atom are calculated using the time-dependent local spin-density approximation. The spectra are dominated by resonances and depend markedly on the cluster size. It is obtained that the resonances have an autoionization character and are caused by the interference between discrete electronic transitions from the 3p shell of the impurity atom to unfilled d shells of the jellium-cluster and ionization excitations ofd electrons. For comparison, within the same approach, photoionization cross sections of atomic Fe, Co, and Ni are computed.