arXiv subjects

Rodolfo Del Sole

Publications and source records attributed to Rodolfo Del Sole.

14 recordsLinked to original sources

arXiv2008

Many-Body meets QM/MM: Application to indole in water solution

Spectral properties of chromophores are used to probe complex biological processes in vitro and in vivo, yet how the environment tunes their optical properties is far from being fully understood. Here we present a method to calculate such properties on large scale systems, like biologically relevant molecules in aqueous solution. Our approach is based on many body perturbation theory combined with quantum-mechanics/molecular-mechanics (QM/MM) approach. We show here how to include quasi-particle and excitonic effects for the calculation of optical absorption spectra in a QM/MM scheme. We apply this scheme, together with the well established TDDFT approach, to indole in water solution. Our calculations show that the solvent induces a redshift in the main spectral peak of indole, in quantitative agreement with the experiments and point to the importance of performing averages over molecular dynamics configurations for calculating optical properties.

physics.chem-ph↗

arXiv2005

Many-body perturbation theory using the density-functional concept: beyond the GW approximation

We propose an alternative formulation of Many-Body Perturbation Theory that uses the density-functional concept. Instead of the usual four-point integral equation for the polarizability, we obtain a two-point one, that leads to excellent optical absorption and energy loss spectra. The corresponding three-point vertex function and self-energy are then simply calculated via an integration, for any level of approximation. Moreover, we show the direct impact of this formulation on the time-dependent density-functional theory. Numerical results for the band gap of bulk silicon and solid argon illustrate corrections beyond the GW approximation for the self-energy.

cond-mat.other↗

arXiv2004

Ab initio study of reflectance anisotropy spectra of a sub-monolayer oxidized Si(100) surface

The effects of oxygen adsorption on the reflectance anisotropy spectrum (RAS) of reconstructed Si(100):O surfaces at sub-monolayer coverage (first stages of oxidation) have been studied by an ab initio DFT-LDA scheme within a plane-wave, norm-conserving pseudopotential approach. Dangling bonds and the main features of the characteristic RAS of the clean Si(100) surface are mostly preserved after oxidation of 50% of the surface dimers, with some visible changes: a small red shift of the first peak, and the appearance of a distinct spectral structure at about 1.5 eV. The electronic transitions involved in the latter have been analyzed through state-by-state and layer-by-layer decompositions of the RAS. We suggest that new interplay between present theoretical results and reflectance anisotropy spectroscopy experiments could lead to further clarification of structural and kinetic details of the Si(100) oxidation process in the sub-monolayer range.

cond-mat.mtrl-sci↗

arXiv2003

Dynamical excitonic effects in metals and semiconductors

The dynamics of an electron--hole pair induced by the time--dependent screened Coulomb interaction is discussed. In contrast to the case where the static electron--hole interaction is considered we demonstrate the occurrence of important dynamical excitonic effects in the solution of the Bethe--Salpeter equation.This is illustrated in the calculated absorption spectra of noble metals (copper and silver) and silicon. Dynamical corrections strongly affect the spectra, partially canceling dynamical self--energy effects and leading to good agreement with experiment.

cond-mat.mtrl-sci↗

arXiv2002

Quasiparticle bandstructure effects on the {\it d} hole lifetimes of copper within the GW approximation

We investigate the lifetime of {\it d} holes in copper within a {\it first--principle} $GW$ approximation. At the $G_0W_0$ level the lifetime of the topmost {\it d} bands are in agreement with the experimental results and are four times smaller than those obtained in the ``on--shell'' calculations commonly used in literature. The theoretical lifetimes and bandstructure, however, worsen when further iterative steps of self-consistency are included in the calculation, pointing to a delicate interplay between self--consistency and the inclusion of vertex corrections. We show that the $G_0W_0$ success in the lifetimes calculation is due to the opening of new ``intraband'' decay channels that disappear at self--consistency.

cond-mat.str-el↗

arXiv2002

First--principles calculation of the plasmon resonance and of the reflectance spectrum of Silver in the GW approximation

We show that the position and width of the plasmon resonance in Silver are correctly predicted by ab--initio calculations including self--energy effects within the GW approximation. Unlike in simple metals and semiconductors, quasiparticle corrections play a key role and are essential to obtain Electron Energy Loss in quantitative agreement with the experimental data. The sharp reflectance minimum at 3.92 eV, that cannot be reproduced within DFT--LDA, is also well described within GW.The present results solve two unsettled drawbacks of linear response calculations for Silver.

cond-mat.str-el↗

arXiv2001

Quasiparticle Electronic structure of Copper in the GW approximation

We show that the results of photoemission and inverse photoemission experiments on bulk copper can be quantitatively described within band-structure theory, with no evidence of effects beyond the single-quasiparticle approximation. The well known discrepancies between the experimental bandstructure and the Kohn-Sham eigenvalues of Density Functional Theory are almost completely corrected by self-energy effects. Exchange-correlation contributions to the self-energy arising from 3s and 3p core levels are shown to be crucial.

cond-mat.str-el↗

arXiv2001

Plane-waves DFT-LDA calculation of the electronic structure and absorption spectrum of Copper

We present an accurate, first-principles study of the electronic structure and absorption spectrum of bulk copper within Density Functional Theory in the Local Density Approximation (DFT-LDA), including the study of intraband transitions. We construct norm-conserving pseudopotentials (PPs) including the 3d shell (and optionally the underlying 3s and 3p shells) in the valence, and requiring a relatively small plane-waves basis (60 and 140 Rydbergs cutoff, respectively). As a consequence, these PPs are strongly non-local, yielding to macroscopically wrong results in the absorption spectrum when momentum matrix elements are computed naively. Our results are compared with experimental photoemission, absorption and electron energy loss data, and suggest non trivial self-energy effects in the quasiparticle spectrum of Cu.

cond-mat.mtrl-sci↗

arXiv2000

Reflectivity Anisotropy Spectra of Cu- and Ag- (110) surfaces from {\it ab initio} theory

We are able to disentagle the effects of the intraband and interband parts of the bulk dielectric function on the bare dielectric anisotropy of the surface. We show how the position, sign and amplitude of the structures observed in such spectra depend on the above quantities. The lineshape of all the calculated structures agree very well with the ones observed experimentally for samples treated by suitable surface cleaning. In particular, we reproduce the observed single peak structure of Ag at high energy, found to represent a state of the clean surface different from the one giving the originally observed double peak structure. This results is not reproduced by the 'local field' model.

cond-mat.mtrl-sci↗

arXiv1999

Surface versus crystal-termination effects in the optical properties of surfaces

We prove, by realistic microscopic calculations within the sp^3s^* Tight Binding method for GaAs (110) and (100), that the surface optical properties are not influenced by long-range crystal termination effects, and hence that they can be consistently studied considering slabs of limited thickness (20 - 30 Å). The origin of derivative-like and bulk-like lineshapes in Reflection Anisotropy Spectra is also discussed, analyzing the effects arising from possible surface-induced reduction, broadening, and shifting of the bulk spectrum near the surface.

cond-mat↗

arXiv1999

Ab initio optical properties of Si(100)

We compute the linear optical properties of different reconstructions of the clean and hydrogenated Si(100) surface within DFT-LDA, using norm-conserving pseudopotentials. The equilibrium atomic geometries of the surfaces, determined from self-consistent total energy calculations within the Car-Parrinello scheme, strongly influence Reflectance Anisotropy Spectra (RAS), showing differences between the p(2x2) and c(4x2)reconstructions. The Differential Reflectivity spectrum for the c(4x2) reconstruction shows a positive peak at energies < 1 eV, in agreement with experimental results.

cond-mat.mtrl-sci↗

arXiv1999

Study of a Nonlocal Density scheme for electronic--structure calculations

An exchange-correlation energy functional beyond the local density approximation, based on the exchange-correlation kernel of the homogeneous electron gas and originally introduced by Kohn and Sham, is considered for electronic structure calculations of semiconductors and atoms. Calculations are carried out for diamond, silicon, silicon carbide and gallium arsenide. The lattice constants and gaps show a small improvement with respect to the LDA results. However, the corresponding corrections to the total energy of the isolated atoms are not large enough to yield a substantial improvement for the cohesive energy of solids, which remains hence overestimated as in the LDA.

cond-mat↗

arXiv1998

Analytical expressions for the local-field factor G(q) and the exchange-correlation kernel K_{xc}(r) of the homogeneous electron gas

We present an analytical expression for the local field factor G(q) of the homogeneous electron gas which reproduces recently published Quantum Monte--Carlo data by S. Moroni, D.M. Ceperley, and G. Senatore [Phys. Rev. Lett. 75, 689 (1995)], reflects the theoretically known asymptotic behaviours for both small and large q limits, and allows to express the exchange-correlation kernel K_{xc} analytically in both the direct and reciprocal spaces. The last property is particularly useful in numerical applications to real solids

cond-mat↗

arXiv1998

Ab initio calculation of excitonic effects in the optical spectra of semiconductors

An ab initio approach to the calculation of excitonic effects in the optical absorption spectra of semiconductors and insulators is formulated. It starts from a quasiparticle bandstructure calculation and is based on the relevant Bethe--Salpeter equation. An application to bulk silicon shows a substantial improvement with respect to previous calculations in the description of the experimental spectrum, for both peak positions and lineshape.

cond-mat↗