Publications by Alfredo Pasquarello

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To assess the accuracy of hybrid functional and many-body GW methods, we study the band offsets for a set of lattice-matched semiconductor heterojunctions, including AlAs/GaAs(100), AlP/GaP(100), Si/GaP(110), Ge/GaAs(110), Ge/AlAs(110), Ge/ZnSe(110), and Z ...

We characterize the transition structure at the Si(100)-SiO2 interface by addressing the inverse ion-scattering problem. We achieve sensitivity to Si displacements at the interface by carrying out ion-scattering measurements in the channeling geometry for varying ion energies. To interpret our experimental results, we generate realistic atomic-scale models using a first-principles approach and carry out ion-scattering simulations based on classical interatomic potentials. Silicon displacements larger than 0

Using a density functional approach, we determine the relative stability of various oxygen species in alpha -quartz. We considered interstitial species in the form of atomic and molecular oxygen, as well as network species, such as peroxyl and ozonyl link-ages. The interstitial molecular oxygen species is found to be the most stable one. The ozonyl link-age lies higher in energy by 1.0 eV. Dissociation of the interstitial O-2 molecule into two peroxyl linkages or into two interstitial oxygen species occurs

Using a density functional scheme, the authors investigate the electronic properties of an epitaxial silicon oxynitride layer on a 6H-SiC(0001) surface, as recently realized experimentally. Simulated scanning-tunneling-microscopy images of filled and empty states agree well with the experiment, lending support to the proposed atomic structure. In accord with the experiment, the local density of states indicates that the electronic band gap in the thin silicate layer at the surface is close to that of bulk S

A first-principle molecular dynamics study on liquid GeSe2 yields structural properties in good agreement with detailed neutron scattering data. The short range order is accurately described by a variety of bonding configurations, in which regular tetrahedra coexist with an important fraction of homopolar bonds and threefold centers. The first sharp diffraction peak in the total structure factor, which characterizes order over intermediate range distances, is also well reproduced. However, this level of the

We present a comparison of the most common finite-size supercell correction schemes for charged defects in density functional theory calculations. Considered schemes include those proposed by Makov and Payne (MP), Lany and Zunger (LZ), and Freysoldt, Neugebauer, and Van de Walle (FNV). The role of the potential alignment is also assessed. Supercells of various sizes are considered and the corrected formation energies are compared to the values obtained by extrapolation to large supercells. For defects with

Various schemes for correcting the finite-size supercell errors in the case of charged defect calculations are analyzed and their performance for a series of defect systems is compared. We focus on the schemes proposed by Makov and Payne (MP), Freysoldt, N ...

Using density functional calculations in the generalized gradient approximation, the energetics of competing atomic processes occuring during the oxidation of silicon are evaluated. Simple molecular systems are used to model the breaking of Si-Si and Si-O bonds in the oxide. These calculations suggest that the breaking of Si-Si bonds and the formation of threefold coordinated O atoms are the most favourable transformation pathways of the bonding network of the oxide, in accord with the atomic processes obse

The method for treating finite electric fields within periodic boundary conditions is used to formally define a density functional depending on the electric field. An exchange and correlation energy functional depending on the electric field is introduced and related to the functional at zero field by a formal expansion with respect to the field. (C) 2004 Wiley Periodicals, Inc.

The electronic and structural properties of the Ge/GeO2 interface are addressed through a density functional simulation scheme which includes the use of hybrid functionals for achieving accurate band gaps, band offsets and defect levels. The present work discusses the germanium dangling bond levels, the thermodynamics of GeOx, the stability of the oxygen vacancy across Ge/HfO2 interfaces, the atomic structure of GeOx, electron and hole trapping in GeOx, and the band alignment at the Ge/GeO2 interface. (C) 2

The electronic and structural properties at the Ge/GeO2 interface are addressed through a density-functional simulation scheme, which includes the use of hybrid functionals for achieving defect levels and band gaps comparable to experiment. The present work discusses the determination of the germanium dangling bond levels, the band alignment in a model structure of the Ge/GeO2 interface, the thermodynamics of GeOx, the stability of the oxygen vacancy across Ge/GeOx/HfO2 stacks, the structural and electronic

We study the infrared absorption spectra of ultrathin SiO2, films on Si(100) using a first-principles approach, and adopting a model Si(100)-SiO2 interface with a realistic transition structure. We calculate both the transverse-optical and the longitudinal-optical infrared absorption spectra across the interface, and show that the red shift of the high-frequency peaks observed experimentally with decreasing oxide thickness originates from the softer vibrational frequencies of the substoichiometric interfaci

Using a first-principles approach, we calculate Si 2p core-level shifts for spherosiloxane H8Si8O12 clusters chemisorbed on Si(001). A chemisorption mechanism that preserves the cage structure of the clusters is assumed. The resulting relaxed surface structure yields shifts consistent with the position and width of the peak at high binding energy in the photoemission spectrum. The role of dielectric effects on core-hole relaxation is essential to achieve this agreement. The other experimentally observed pea

We report on the strengths and limitations of scanning tunnelling microscopy (STM) when used for characterising atomic-scale features of quasi two-dimensional materials, such as graphene and single layers of hexagonal boron nitride, which may present stron ...

A first-principle approach allows the study of relaxed structural models for surfaces and interfaces. This is a powerful tool for the study of the local bonding. The utility of the first-principle theory is substantially extended through the calculation of core-level shifts. Such results can be used in conjunction with measured photoemission spectra to make progress in understanding the local atomic structure at interfaces. We review the quantitative comparison of the calculated core level shifts with exper

Using a first-principles approach, we investigate the effect of interdimer interactions on N Is core-level shifts at the NH3 saturated Si(100)-2 X 1 surface. Fully relaxed model structures are generated in which -NH2 groups on adjacent dimers in a row are located either on opposite ends (OE) or on the same ends of the respective dimers. By comparing calculated core-level shifts with measured photoemission spectra, we show that the OE configuration dominates, supporting the occurrence of an ordered coverage

Homogeneous electric fields are treated within density functional calculations with periodic boundary conditions. A nonlocal energy functional depending on the applied field is used within an ab initio molecular dynamics scheme. The reliability of the method is demonstrated in the case of bulk MgO for the Born effective charges, and the high- and low-frequency dielectric constants.

By using first-principle molecular dynamics within density functional theory, we study the structural properties of amorphous GeSe2 at a temperature T of 300 K. For each property, a statistical average is obtained from six independent partial averages taken on temporal trajectories, each one lasting 12 ps. Each trajectory stems from an initial configuration of the liquid phase at T=1100 K and is generated by extensive annealing at T=300 K. Overall, our level of theory provides a picture of this prototypical

We study the formation energies of native point defects in GaN through density-functional theory. In our first-principles scheme, the band edges are positioned in accord with hybrid density functional calculations, thus yielding a band-gap in agreement wit ...

We propose a method within density functional theory for aligning defect energy levels at interfaces without relying on experimental data. We apply our scheme to the alignment of charge transition levels of the interstitial hydrogen and the hydrogen bridge defect (-Si-H-Si-) at the Si-SiO2 interface. We find that the +/- charge transition level of the interstitial hydrogen is located in the upper part of the silicon band gap. The defect level alignment obtained in our scheme supports that the hydrogen bridg

Alfredo Pasquarello

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Band offsets of lattice-matched semiconductor heterojunctions through hybrid functionals and G(0)W(0)

Transition structure at the Si(100)-SiO2 interface

Oxygen species in SiO2: a first-principles investigation

Electronic properties of an epitaxial silicon oxynitride layer on a 6H-SiC(0001) surface: A first-principles investigation

Microscopic structure of liquid GeSe2: The problem of concentration fluctuations over intermediate range distances

Comparison between various finite-size supercell correction schemes for charged defect calculations

Finite-size supercell correction schemes for charged defect calculations

Network transformation processes during oxidation of silicon

Density functional theory with finite electric field

First principles study of electronic and structural properties of the Ge/GeO2 interface

Electronic and structural properties at Ge/GeO2 interfaces: A density-functional investigation

Infrared properties of ultrathin oxides on Si(100)

Spherosiloxane H8Si8O12 clusters on Si(001): First-principles calculation of Si 2p core-level shifts

Giant apparent lattice distortions in STM images of corrugated sp2-hybridised monolayers

Core-level shifts in Si(001)-SiO2 systems: The value of first-principle investigations

Nitrogen 1s core-level shifts at the NH3 saturated Si(100)-2 x 1 surface: a first-principles study

Finite electric field in density functional calculations with periodic boundary conditions

Short and intermediate range order in amorphous GeSe2

Energetics of native point defects in GaN: A density-functional study

Alignment of hydrogen-related defect levels at the Si-SiO2 interface