arXiv subjects

J. M. Pitarke

Publications and source records attributed to J. M. Pitarke.

At least 73 records · Page 4Linked to original sources

arXiv2001

An inhomogeneous and anisotropic Jastrow function for non-uniform many-electron systems

Quantum Monte Carlo simulations of interacting electrons in solids often use Slater-Jastrow trial wave functions. The Jastrow function takes into account correlations between pairs of electrons. In simulations of solids, it is common to use a Jastrow function which is both homogeneous and isotropic. The use of a homogeneous and isotropic Jastrow factor is questionable in applications to systems with strong density inhomogeneities, such as surfaces and multilayers. By generalizing the original derivation of the RPA Jastrow factor for the homogeneous electron gas [Gaskell] to inhomogeneous systems we derive an scheme for generating inhomogeneous and anisotropic Jastrow factors for use in nonuniform systems, from the non-interacting static structure factor and density of the system. We discuss aspects of our scheme and illustrate it with a first application to an inhomogeneous electron gas.

cond-mat.mtrl-sci↗

arXiv2001

Dynamic structure factor of gold

We have investigated the role of localized {\it d} bands in the dynamical response of Au, on the basis of {\it ab initio} pseudopotential calculations. The density-response function has been evaluated in the random-phase approximation. For small momenta, we have found a double peak structure in the energy-loss function, which results from the presence of {\it d} electrons. These results are in good agreement with the experimentally determined optical response of gold. We also analyze the dependence of the dynamical structure factor on the wave vector {\bf q}.

cond-mat.mtrl-sci↗

arXiv2000

Thin-film effects on the surface stopping power of a free electron gas

The electronic properties of thin films present quantum-size effects, which are a consequence of the finite size of the system. Here we focus on the investigation of these effects on the electronic energy loss of charged particles moving parallel with thin metallic films. The energy loss is calculated, within linear-response theory, from the knowledge of the density-response function of the inhomogeneous electron system, which we evaluate either in the random-phase approximation or with the use of an adiabatic and local exchange-correlation kernel.

cond-mat.mtrl-sci↗

arXiv2000

Recent Progress in the Computational Many-Body Theory of Metal Surfaces

In this article we describe recent progress in the computational many-body theory of metal surfaces, and focus on current techniques beyond the local-density approximation of density-functional theory. We overview various applications to ground and excited states. We discuss the exchange-correlation hole, the surface energy, and the work function of jellium surfaces, as obtained within the random-phase approximation, a time-dependent density-functional approach, and quantum Monte Carlo methods. We also present a survey of recent quasiparticle calculations of unoccupied states at both jellium and real surfaces.

cond-mat.mtrl-sci↗

arXiv2000

Electronic response of aligned multishell carbon nanotubes

We report calculations of the effective electronic response of aligned multishell carbon nanotubes. A local graphite-like dielectric tensor is assigned to every point of the multishell tubules, and the effective transverse dielectric function of the composite is computed by solving Maxwell's equations. Calculations of both real and imaginary parts of the effective dielectric function are presented, for various values of the filling fraction and the ratio of the internal and external radii of hollow tubules. Our full calculations indicate that the experimentally measured macroscopic dielectric function of carbon nanotube materials is the result of a strong electromagnetic coupling between the tubes, which cannot be accounted for with the use of simplified effective medium theories. The presence of surface plasmons is investigated, and both optical absorption cross sections and energy-loss spectra of aligned tubules are calculated.

cond-mat.mtrl-sci↗

arXiv2000

Jellium surface energy beyond the local-density approximation: Self-consistent-field calculations

We report extensive self-consistent calculations of jellium surface energies, by going beyond the local-density approximation. The density-response function of a bounded free-electron gas is evaluated within the random-phase approximation, with use of self-consistent electron density profiles. The exchange-correlation energy is then obtained from an exact adiabatic fluctuation-dissipation formula. We also investigate quantum-size effects and the extrapolation of finite-slab calculations to the infinite-width limit.

cond-mat.mtrl-sci↗

arXiv2000

Surface-state electron dynamics in noble metals

Theoretical investigations of surface-state electron dynamics in noble metals are reported. The dynamically screened interaction is computed, within many-body theory, by going beyond a free-electron description of the metal surface. Calculations of the inelastic linewidth of Shockley surface-state electrons and holes in these materials are also presented. While the linewidth of excited holes at the surface-state band edge (${\bf k}_\parallel=0$) is dominated by a two-dimensional decay channel, within the surface-state band itself, our calculations indicate that major contributions to the electron-electron interaction of surface-state electrons above the Fermi level come from the underlying bulk electrons.

cond-mat.mtrl-sci↗

arXiv2000

Metallic slabs: Perturbative treatments based on jellium

We examine first-order perturbative results based on jellium for the surface energy of slabs of simple metals, using various local pseudopotentials (Ashcroft, Heine-Abarenkov and evanescent core). The difference between the pseudopotential and the jellium potential is averaged along the plane parallel to the surface. We compare these perturbative results with those of the stabilized jellium model (a modification of the regular jellium model in which the perturbation appears in the energy functional right from the outset) and with the output of other perturbative and non-perturbative calculations.

cond-mat.mtrl-sci↗

arXiv2000

Hole dynamics in noble metals

We present a detailed analysis of hole dynamics in noble metals (Cu and Au), by means of first-principles many-body calculations. While holes in a free-electron gas are known to live shorter than electrons with the same excitation energy, our results indicate that d-holes in noble metals exhibit longer inelastic lifetimes than excited sp-electrons, in agreement with experiment. The density of states available for d-hole decay is larger than that for the decay of excited electrons; however, the small overlap between d- and sp-states below the Fermi level increases the d-hole lifetime. The impact of d-hole dynamics on electron-hole correlation effects, which are of relevance in the analysis of time-resolved two-photon photoemission experiments, is also addressed.

cond-mat.mtrl-sci↗

arXiv2000

Nonlinear interaction of charged particles with a free electron gas beyond the random-phase approximation

A nonlinear description of the interaction of charged particles penetrating a solid has become of basic importance in the interpretation of a variety of physical phenomena. Here we develop a many-body theoretical approach to the quadratic decay rate, energy loss, and wake potential of charged particles moving in an interacting free electron gas. Explicit expressions for these quantities are obtained either within the random-phase approximation (RPA) or with full inclusion of short-range exchange and correlation effects. The Z^3 correction to the energy loss of ions is evaluated beyond RPA, in the limit of low velocities.

cond-mat.mtrl-sci↗

arXiv2000

The role of occupied d states in the relaxation of hot electrons in Au

We present first-principles calculations of electron-electron scattering rates of low-energy electrons in Au. Our full band-structure calculations indicate that a major contribution from occupied d states participating in the screening of electron-electron interactions yields lifetimes of electrons in Au with energies of $1.0-3.0 {\rm eV}$ above the Fermi level that are larger than those of electrons in a free-electron gas by a factor of $\sim 4.5$. This prediction is in agreement with a recent experimental study of ultrafast electron dynamics in Au(111) films (J. Cao {\it et al}, Phys. Rev. B {\bf 58}, 10948 (1998)), where electron transport has been shown to play a minor role in the measured lifetimes of hot electrons in this material.

cond-mat.mtrl-sci↗

arXiv2000

Slabs of stabilized jellium: Quantum-size and self-compression effects

We examine thin films of two simple metals (aluminum and lithium) in the stabilized jellium model, a modification of the regular jellium model in which a constant potential is added inside the metal to stabilize the system for a given background density. We investigate quantum-size effects on the surface energy and the work function. For a given film thickness we also evaluate the density yielding energy stability, which is found to be slightly higher than the equilibrium density of the bulk system and to approach this value in the limit of thick slabs. A comparison of our self-consistent calculations with the predictions of the liquid-drop model shows the validity of this model.

cond-mat.mtrl-sci↗

arXiv2000

First-principles calculations of hot-electron lifetimes in metals

First-principles calculations of the inelastic lifetime of low-energy electrons in Al, Mg, Be, and Cu are reported. Quasiparticle damping rates are evaluated from the knowledge of the electron self-energy, which we compute within the GW approximation of many-body theory. Inelastic lifetimes are then obtained along various directions of the electron wave vector, with full inclusion of the band structure of the solid. Average lifetimes are also reported, as a function of the electron energy. In Al and Mg, splitting of the band structure over the Fermi level yields electron lifetimes that are smaller than those of electrons in a free-electron gas. Larger lifetimes are found in Be, as a result of the characteristic dip that this material presents in the density of states near the Fermi level. In Cu, a major contribution from $d$ electrons participating in the screening of electron-electron interactions yields electron lifetimes which are well above those of electrons in a free-electron gas with the electron density equal to that of valence ($4s^1$) electrons.

cond-mat.mtrl-sci↗

arXiv1999

Polarization induced by charged particles in real solids

We report a first-principles description of the induced wake potential and density in real solids. The linear-response formalism is used to obtain the potential and density induced by an external charge penetrating through an inhomogeneous periodic system. The linear dynamical response of the system is evaluated in the random-phase approximation, by including the full band structure of the solid. The impact of the periodic crystalline potential is analyzed, and variations of the wake along different channels in Al and Si are investigated.

cond-mat.mtrl-sci↗

arXiv1999

Band structure effects on the interaction of charged particles with solids

A survey is presented of current investigations of the impact of band structure effects on various aspects of the interaction of charged particles with real solids. The role that interband transitions play in the decay mechanism of bulk plasmons is addressed, and results for plasmon linewidths in Al and Si are discussed. {\it Ab initio} calculations of the electronic energy loss of ions moving in Al and Si are also presented, within linear response theory, from a realistic description of the one-electron band structure and a full treatment of the dynamic electronic response of valence electrons. Both random and position-dependent stopping powers of valence electrons are computed.

cond-mat.mtrl-sci↗

arXiv1999

Hydrodynamic approximation for the nonlinear response of a metal surface

We present semi-classical and quantized hydrodynamic models to obtain the quadratic electronic response of a plane-bounded electron gas. Explicit expressions for the dynamic image potential experienced by charged particles moving near a jellium surface are derived, up to third order in the projectile charge. These expressions are employed to compute the image potential at all distances outside the surface. Though nonlinear corrections are found to be more important far inside the solid than outside, our results indicate that the nonlinear image potential is enhanced with respect to the linear image potential by a factor that is for Al as large as $\sim 1.15$ near the surface in the case of a stationary particle ($v\to 0$) with positive unit charge $e$.

cond-mat.mtrl-sci↗

arXiv1999

Self-energy of image states on copper surfaces

We report extensive calculations of the imaginary part of the electron self-energy in the vicinity of the (100) and (111) surfaces of Cu. The quasiparticle self-energy is computed by going beyond a free-electron description of the metal surface, either within the GW approximation of many-body theory or with inclusion, within the GW$Γ$ approximation, of short-range exchange-correlation effects. Calculations of the decay rate of the first three image states on Cu(100) and the first image state on Cu(111) are also reported, and the impact of both band structure and many-body effects on the electron relaxation process is discussed.

cond-mat.mtrl-sci↗

arXiv1999

Theory of inelastic lifetimes of low-energy electrons in metals

Electron dynamics in the bulk and at the surface of solid materials are well known to play a key role in a variety of physical and chemical phenomena. In this article we describe the main aspects of the interaction of low-energy electrons with solids, and report extensive calculations of inelastic lifetimes of both low-energy electrons in bulk materials and image-potential states at metal surfaces. New calculations of inelastic lifetimes in a homogeneous electron gas are presented, by using various well-known representations of the electronic response of the medium. Band-structure calculations, which have been recently carried out by the authors and collaborators, are reviewed, and future work is addressed.

cond-mat.mtrl-sci↗