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We discuss the key steps that have to be followed to calculate quantum transport out of equilibrium by means of the {\it ab initio} Gaussian Embedded Cluster Method recently developed by the authors. Our main aim is to emphasize through several examples that, if a sufficiently large portion of the electrodes is included in the {\it ab initio} calculation, which does also incorporate an electrochemical potential difference $\mu_L-\mu_R=eV$, there is no need to impose an electrostatic potential $V$ drop accross the system., Comment: 4 pages, 4 figures, submitted to Physical Review B

Level and wavefunction statistics have been studied for two dimensional clusters of the square lattice in the presence of random magnetic fluxes. Fluxes traversing lattice plaquettes are distributed uniformly between - (1/2) Phi_0 and (1/2) Phi_0 with Phi_0 the flux quantum. All considered statistics start close to the corresponding Wigner-Dyson distribution for small system sizes and monotonically move towards Poisson statistics as the cluster size increases. Scaling is quite rapid for states close to the band edges but really difficult to observe for states well within the band. Localization properties are discussed considering two different scenarios. Experimental measurement of one of the considered statistics --wavefunction statistics seems the most promising one-- could discern between both possibilities. A real version of the previous model, i.e., a system that is invariant under time reversal, has been studied concurrently to get coincidences and differences with the Hermitian model., Comment: 12 twocolumnn pages in revtex style, 17 postscript figures, to be published in PRB, send comments to jav@boston.icmm.csic.es

Quantum chaotic dynamics is obtained for a tight-binding model in which the energies of the atomic levels at the boundary sites are chosen at random. Results for the square lattice indicate that the energy spectrum shows a complex behavior with regions that obey the Wigner-Dyson statistics and localized and quasi-ideal states distributed according to Poisson statistics. Although the averaged spatial extension of the eigenstates in the present model scales with the size of the system as in the Gaussian Orthogonal Ensemble, the fluctuations are much larger., Comment: 4 twocolumnn pages in revtex style, 4 postscript figures, to be published in PRL, send comments to jav@boston.icmm.csic.es

Persistent currents in mesoscopic metallic rings induced by static magnetic fields are investigated by means of a Hamiltonian which incorporates diagonal disorder and the electron-electron interaction through a Hubbard term ($U$). Correlations are included up to second order perturbation theory which is shown to work accurately for $U$ of the order of the hopping integral. If disorder is not very strong, interactions increase the current up to near its value for a clean metal. Averaging over ring lengths eliminates the first Fourier component of the current and reduces its value, which remains low after interactions are included., Comment: uuencoded gzipped tar file containing the manuscript (tex file) and four figures (postscript files). Accepted for publication in Solid State Communications. Send e-mail to: jav@boston.icmm.csic.es

It is shown that the peak structure observed in angle-resolved photoelectron spectra of metallic deposits can only be unambiguously associated to single electronic states if the deposit has a two dimensional character (finite along one spatial direction). In one and zero dimensions the density of states shows peaks related to bunches of single electron states (the finer structure associated to the latter may not always be experimentally resolved). The characteristics of the peak structure strongly depend on the band dispersion in the energy region where they appear. Results for the density of states and photoemission yield for Ag crystallites on GaAs(110) are presented and compared with experimental photoelectron spectra., Comment: Uuencoded gz-compressed postcript file including text and three figures; Send comments to jav@boston.icmm.csic.es

The low energy spin and charge excitations in the 2D Hubbard model near half filling are analyzed. The RPA spectra derived from inhomoheneous mean field textures are analyzed. Spin excitations show a commensurate peak at half filling, incommensurate peaks near half filling, and a broad background typical of a dilute Fermi liquid away from half filling. Charge excitations, near half filling, are localized near (0,0), and they occupy a small portion of the Brillouin Zone, in a way consistent with the existence of a small density of carriers, and a small Fermi surface. At higher hole densities, they fill the entire BZ, and can be understood in terms of a conventional Fermi liquid picture. The results are consistent with the observed features of the high-T$_c$ superconductors., Comment: Latex manuscript (4 pages) + 4 postscript figures (upon request)

The wavefunction renormalization in the Hubbard model is studied, by using well tested mean field tecniques. The 'orthogonality catastrophe' is shown to exist, even in 2D, for doping levels sufficiently close to half filling. The results are extended beyond mean field, by constructing delocalized wavefunctions, with the correct symmetries of the exact solutions. The physics are still well described by the assumption of the existence of the orthogonality catastrophe., Comment: 8 pages

The applicability of the Hartree-Fock and random phase approximations to models of strongly correlated electrons is discussed. The 2D Hubbard model is analyzed. An antiferromagnetic phase (at half filling) and Fermi liquid behavior (at low electron densities) are found. In addition, the system shows an unconventional regime near half filling. It is characterized by the formation of spin and charge textures. Local magnetic moments and spin waves are also present, and the quasiparticle pole at the Fermi energy vanishes. The charge excitation spectrum is gapless. The overall features resemble those of the 1D Luttinger liquid., Comment: 8 pages. Latex