Publications de Alfredo Pasquarello

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The occurrence of an ultrathin SiO2 oxide layer at the interface between silicon and high-k dielectrics in metal-oxide-semiconductor devices contributes to degrading the capacitance of the gate stack. In this work, we investigate the dielectric and infrared properties of atomically thin SiO2 layers on Si(100) through a fully quantum-mechanical description. For this purpose, we construct atomistic models of the Si(100)-SiO2 interface on the basis of available experimental data, by using both classical and fi

Within many-body perturbation theory, we calculate band offsets for a set of epitaxial interfaces, including AlP/GaP, AlAs/GaAs, Ge/AlAs, Ge/GaAs, Ge/ZnSe, Si/GaP, ZnSe/GaAs, and CaF2/Si. We consider various quasiparticle self-consistent GW schemes with or ...

We report on a first-principles investigation of the structural and vibrational properties of vitreous germania (v-GeO2). Our work focuses on a periodic model structure of 168 atoms, but three smaller models are also studied for comparison. We first carry out a detailed structural analysis both in real and reciprocal spaces. Our study comprises the partial pair correlation functions, the angular distributions, the total neutron correlation function, the neutron and x-ray total structure factors, and the Fab

We investigate at the atomic scale the oxygen diffusion process occurring during silicon oxidation. First, we address the energetics of several oxygen species in the oxide using density-functional calculations. Our results support the interstitial O-2 molecule as the most stable oxygen species. We then adopt a classical scheme for describing the energetical and topological properties of the percolative diffusion of the O-2 molecule through the interstitial network of the oxide. By studying a large set of di

A procedure for calculating the resonance width of a state degenerate with a continuum is proposed. It is based on a diagonalization of the Hamiltonian on a finite variational basis followed by application of the Fano theory on the resulting eigenstates. The method is first tested on a one-dimensional model that admits an exact solution, and then applied to the problem of the light-hole (LH) exciton in narrow GaAs-Ga(1-x)Al(x)As quantum wells. The resonance width of the LH exciton is found to be of the orde

A model structure of vitreous silica, for which the vibrational frequencies and eigenmodes were calculated from first principles, is used to investigate vibrational amplitudes. Calculated mean-square displacements for oxygen and silicon atoms are obtained as a function of temperature. The square displacement tensors of oxygen atoms show a marked anisotropic character, which is related to the local geometry. The displacements of oxygen atoms along the three principal directions can be associated to distinct

Metal-halide perovskites exhibit high efficiencies in photovoltaic applications and low recombination rates, despite the high concentrations of intrinsic defects. We here study the hole trapping at the negative iodine interstitial, which corresponds to the ...

We review the structural and hyperfine properties of Si dangling bond defects occurring in amorphous SiO2 and at various Si-SiO2 interfaces. These defects have in common a singly occupied orbital on a, trivalent Si Centre. We first briefly summarize the most important methodologies for calculating hyperfine parameters, pointing out their advantages and drawbacks. The properties of the defect centres composed Of Si equivalent to SinO3-n kernels, with n varying from 0 to 3, are then discussed in a,systematic

We study proton diffusion in amorphous SiO2 and hafnium silicates at the atomic scale. In amorphous SiO2, ab initio molecular dynamics suggest that the dominant atomic process consists in cross-ring interoxygen hopping assisted by network vibrations. In ha ...

We develop a theory for investigating atomic-scale dielectric permittivity profiles across interfaces between insulators. A local susceptibility chi(x;omega) is introduced to describe variations of the dielectric response over length scales of the order of interatomic distances. The nonlocality of the microscopic susceptibility tensor chi(ij)(r,r';omega) occurs at smaller distances and therefore does not intervene in our formulation. The local permittivity is obtained from the microscopic charge density ind

Using a density-functional scheme, we study the structural and vibrational properties of vitreous germanium diselenide (v-GeSe2). Through the use of classical and first-principles molecular-dynamics methods, we generate a set of structural models showing a varying degree of chemical disorder. In particular, two types of structural concepts are represented: one in which the tetrahedral order is preserved to a very large extent, and one which reproduces the high degree of disorder in first-neighbor shells fou

We develop a computationally efficient scheme to accurately determine finite-temperature band gaps for metal halide perovskites belonging to the class ABX(3) (A = Rb, Cs; B = Ge, Sn, Pb; and X = F, Cl, Br, I). First, an initial estimate of the band gap is ...

Diffusion of carbon is the crucial step in chemical vapor deposition (CVD) growth of carbon nanotubes (CNTs) On metal nanoparticles. Using first principles techniques we model the binding and diffusion of carbon atoms and dimers on late transition (Ni, Pd, Pt) and coinage (Cu, Ag, Au) metal catalysts. We consider various diffusion mechanisms including both surface and subsurface channels, finding the lowest activation barriers for carbon adatoms on nanoparticles of coinage metals. For these metals, our calc

Using density-functional calculations, we investigate the possibility of ammonia synthesis at supported Fe nanoclusters along catalytic routes closely resembling those in biological nitrogen fixation. To achieve similar catalytic conditions as at the activ ...

We discuss the structural, electronic and dielectric properties of a model structure of the Si(100)-SiO2 interface that accounts for the amorphous nature of the oxide. After showing that the structural properties of this model are consistent with a variety of experimental data, we consider the variation of the valence and conduction band edges across the interface. Our calculations indicate that the width of the electronic structure transition from the substrate to the oxide is 0.7-0.8 nm. We also address t

Periodically corrugated epitaxial graphene and hexagonal boron nitride (h-BN) on metallic substrates are considered as perspective templates for the self-assembly of nanoparticles arrays. By using first-principles calculations, we determine binding energie ...

To address the slow recombination of photogenerated charges in tetragonal CH 3 NH 3 PbI 3 , the evolution of extra electrons and holes is simulated through advanced ab initio molecular dynamics. We show that the localization of the charge carriers and thei ...

claim (i) that our estimate is only based on the analysis of Raman spectra which are notoriously difficult to calculate, (ii) that we inappropriately obtained the value of f 0:75 on the basis of the Raman spectrum of a model structure with f 0:09, and (iii) that 11 B NMR spectra are insensitive to f. We here show that these claims are unsubstantiated. The accuracy of Raman intensities and frequencies as obtained within density functional schemes has amply been demonstrated for a variety of systems including

The charge "belonging" to a given atom in a condensed system is not a measurable quantity, and can be defined only by means of some arbitrary model and/or theory: the static dipole (or multipole) associated with a given molecule in a molecular solid or liquid is analogously ill-defined. At variance with this, the dynamical (alias infrared, IR) atomic charge is a well defined quantity, much studied in recent years for various materials: it measures the coupling of atomic displacements to macroscopic electric

The properties of interstitial and substitutional Li in wurtzite ZnO are modeled using hybrid density functional calculations. We investigate the impact of the band-gap error on the formation energies of the two defects and their dependence on the Fermi le ...

Alfredo Pasquarello

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Dielectric and infrared properties of ultrathin SiO2 layers on Si(100)

Band alignments through quasiparticle self-consistent GW with efficient vertex corrections

Vibrational spectra of vitreous germania from first-principles

Multiscale modeling of oxygen diffusion through the oxide during silicon oxidation

Variational Calculation of Fano Linewidth - Application to Excitons in Quantum-Wells

Vibrational amplitudes in vitreous silica

Mechanism suppressing charge recombination at iodine defects in CH3NH3PbI3 by polaron formation

Modelling of paramagnetic trivalent silicon defect centres in amorphous silica and at Si-SiO2 interfaces

Proton Diffusion in Amorphous SiO2 and Hafnium Silicate by Ab Initio Molecular Dynamics

Theory of atomic-scale dielectric permittivity at insulator interfaces

First-principles investigation of the structural and vibrational properties of vitreous GeSe2

Accurate and efficient band-gap predictions for metal halide perovskites at finite temperature

Carbon diffusion in CVD growth of carbon nanotubes on metal nanoparticles

Nitrogen fixation at passivated Fe nanoclusters supported by an oxide surface: Identification of viable reaction routes using density functional calculations

Atomic-scale modelling of the Si(100)-SiO2 interface

Metal adatoms on graphene and hexagonal boron nitride: Towards rational design of self-assembly templates

Origin of low electron-hole recombination rate in metal halide perovskites

Comment on "fraction of boroxol rings in vitreous boron oxide from a first-principles analysis of Raman and NMR spectra" - Umari and Pasquarello reply

A generalization of the effective-charge concept: Dynamical multipoles in molecular solids and liquids

A hybrid density functional study of lithium in ZnO: Stability, ionization levels, and diffusion