Publications de Alfredo Pasquarello

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A finite-size supercell correction scheme is introduced for the formation energy of charged defects at surfaces and interfaces. The scheme combines classical electrostatics with the dielectric profile and the electrostatic potential extracted from the elec ...

We investigate the dielectric screening across the Si-SiO2 interface using a first-principle approach. By determining the profile of the microscopic polarization and the effective polarizabilities of SiOn (n = 0,..4) structural units, we show that the variation of the local screening across the interface relates to the chemical grading. The oxide region near the Si substrate shows the same dielectric permittivity as bulk SiO2 as long as the oxide is locally stoichiometric. The suboxide region carries an enh

Hybrid density functional calculations and atomistic models are used to study point defects in III-V compounds. We first study dangling-bonds in InxGa1-xAs. In GaAs, the cation dangling-bond levels are found in the upper part of the band gap, but they are ...

Quantum mechanical simulations that include the effects of the liquid environment are highly relevant for the characterization of solid-liquid interfaces, which is crucial for the design of a wide range of devices. In this work we present a rigorous and sy ...

We study structural and electronic properties of the oxygen vacancy in monoclinic HfO 2 for five different charge states. We use a hybrid density functional to accurately reproduce the experimental band gap. To compare with measured defect levels, we deter ...

The bifunctional mechanism for the oxygen evolution reaction (OER) involving two distinct reaction sites is studied through the computational hydrogen electrode method for a set of catalyst materials including rutile TiO2(110), anatase TiO2(101), SnO2(110) ...

In the attempt to identify the physical origin of a first sharp diffraction peak (FSDP) in the concentration-concentration partial structure factor, we perform first-principle molecular dynamics of liquid GeSe2. We compare the structural properties of two set of simulations, which differ by their treatment of the electronic structure. This is achieved by considering different energy cutoffs defining the plane-wave basis sets, the higher energy cutoff leading to a moderate enhancement of the ionicity in the

Using a density-functional scheme, we study the migration of a single O atom in a (110) plane between two adjacent bond-center sites in bulk Si. The minimum energy migration path is found through the nudged elastic band method within a generalized gradient ...

A set of low-strain commensurate interface structures for epitaxial graphene on SiC(0001) are obtained by combining rotated graphene supercells with m x m or m root 3 x m root 3R30 degrees SiC cells. For two among the interfaces with lowest strain, corresp ...

We introduce an atomistic model structure of the Si(1 0 0)-SiO2 interface which incorporates atomic-scale information from a variety of experimental probes. The interface model consists of a disordered, topologically perfect oxide network matching the Si substrate without coordination defects. The transition region on the substrate side shows a disordered bonding pattern extending over about two monolayers and including several in-plane Si-Si dimers. On the oxide side, the suboxide matches the amount, the d

We have carried out an ab initio molecular dynamics simulation of liquid oxygen, a molecular fluid in which the individual 02 units carry a molecular magnetic moment. In addition to the atomic and electronic structures, our simulation describes the evolution of the noncollinear magnetic structure. The atomic structure shows a strong preference for parallel alignment of first-neighbour molecules. The magnetic structure shows strong short-range antiferromagnetic correlations, in agreement with spin-polarized

We develop a plane-wave pseudopotential scheme for noncollinear magnetic structures, based on a generalized local spin-density theory in which the direction of the magnetization is a continuous variable of position. We allow the atomic and magnetic structures to relax simultaneously and self-consistently. Application to small Fe clusters yields noncollinear magnetic structures for Fe-3 and Fe-5. The components of the magnetization density vary smoothly with position. The spin direction undergoes sizable cha

We discuss the ab initio modeling of several processes occurring during silicon oxidation with a particular emphasis on the charge state of the diffusing oxygen molecule. For values of the electron chemical potential falling in the range of the silicon ban ...

The formation energies and charge transition levels of vacancy and antisite defects in GaAs and In0.5Ga0.5As are calculated through hybrid density functionals. In As-rich conditions, the As antisite is the most stable defect in both GaAs and InGaAs, except ...

The structural, electronic, and dielectric properties of barrier -type anodic Al oxides prepared with various thicknesses have been investigated. The planar and cross morphologies as well as the surface charge distribution were investigated as a function o ...

We introduce a variational total-energy functional to treat finite homogeneous electric fields with periodic boundary conditions and show that this functional can be implemented within a Car-Parrinello molecular dynamics scheme. The Coupling to an electric field is achieved through the Berry-phase expression of the polarization. The minimization of this extended functional gives a ground state which describes the polarized state in ail electric field. For a crystalline system, the ground state of this exten

A transient state of the excess electron in liquid water preceding the development of the solvation shell, the so-called wet electron, has been invoked to explain spectroscopic observations, but its binding energy and atomic structure have remained highly ...

The vibrational properties of vitreous GeSe2 are studied within the Becke-Lee-Yang-Parr (BLYP) generalized gradient approximation to density functional theory. For this purpose, we consider two models. The first one is derived from a chemically ordered net ...

The photo-active MIL-125 and MIL-125-NH2 metal-organic frameworks (MOFs), despite having a very similar crystalline structure, exhibit different optical behaviors. Luminescence in MIL-125 decays in about 1 ns, while for its amino counterpart, the lifetime ...

Using a density functional approach, we study structural and magnetic properties of small Fe-n clusters (nless than or equal to8) deposited on a MgO(100) substrate. Upon deposition, the clusters closely preserve their gas-phase structure. The magnetic moments for the adsorbed clusters exceed the value for bulk Fe. Compared to the gas phase, significant reductions in the magnetic moments are found for Fe-n clusters with nless than or equal to6. These reductions result from intracluster charge rearrangements

Alfredo Pasquarello

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Finite-Size Supercell Correction for Charged Defects at Surfaces and Interfaces

Atomic-scale investigation of the dielectric screening at the interface between silicon and its oxide

Identification of defect levels at InxGa1-xAs/oxide interfaces through hybrid functionals

Absolute band alignment at semiconductor-water interfaces using explicit and implicit descriptions for liquid water

Structural and electronic properties of oxygen vacancies in monoclinic HfO2

Oxygen evolution reaction: Bifunctional mechanism breaking the linear scaling relationship

Concentration fluctuations on intermediate range distances in liquid GeSe2: the critical role of ionicity

Minimum energy path and atomistic mechanism of the elementary step in oxygen diffusion in silicon: A density-functional study

Low-strain interface models for epitaxial graphene on SiC(0001)

Atomistic model structure of the Si(100)-SiO2 interface from a synthesis of experimental data

Structural and magnetic correlations in liquid oxygen: an ab initio molecular dynamics study

Fully unconstrained approach to noncollinear magnetism: Application to small Fe clusters

Modeling of atomic-scale processes during silicon oxidation: charge state of the O2 molecule

Comparison of vacancy and antisite defects in GaAs and InGaAs through hybrid functionals

Electronic and structural characterization of barrier-type amorphous aluminium oxide

Car-Parrinello Molecular Dynamics in a Finite Homogeneous Electric Field

Picture of the wet electron: a localized transient state in liquid water

Vibrational properties of vitreous GeSe2 with the Becke-Lee-Yang-Parr density functional

On the Electronic and Optical Properties of Metal-Organic Frameworks: Case Study of MIL-125 and MIL-125-NH2

Supported Fe nanoclusters: Evolution of magnetic properties with cluster size