Publications de Alfredo Pasquarello

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Local density functional theory within the framework of the Car-Parrinello method has been used to study the structural parameters and the energetics of offretite, when a Si4+ ion is substituted by (Al3+, H+). The calculations have been performed on a periodically repeated unit cell with 54 atoms and a proton. in agreement with previous cluster calculations, we conclude that the sites with the lowest (Al, H)/Si substitution energies are also those with the largest proton affinity. In addition a correlation

Equilibrium positions on the Li+-PEO and on the Cu++-PEO ground state potential energy surfaces have been determined by ab initio molecular dynamics. Our results confirm the previously proposed jump mechanism for ion diffusion in polymer electrolytes. The energy barriers for Li+ and Cu++ ionic diffusion along the PEO chain have been estimated. (C) 1998 American Institute of Physics.

Using a density-functional approach, we investigate the reactivity of supported metal nanoclusters. We focus on the sequential adsorption of N-2 molecules on a Fe nanocluster supported by an MgO substrate. For an increasing number of N atoms preadsorbed on the nanocluster, we found that the binding energy of the N-2 molecule increases, and can become higher than that of its dissociation products, in marked contrast with the behavior at the respective metallic surface. We identify the electrostatic interacti

The determination of band alignments and defect levels is demonstrated for the technologically relevant Si-SiO2-HfO2 gate stack. The proposed scheme, which combines first-principles molecular dynamics for model generation and hybrid density functionals for electronic-structure calculations, yields band offsets in close agreement with experiment. Charge transition and pinning levels associated with oxygen vacancies are aligned with respect to the silicon band edges. The vacancies are shown to preferentially

We develop a method to determine redox levels of half reactions through the use of ab initio molecular dynamics evolving at constant Fermi energy. This scheme models the effect of an electrode by controlling the charge transfer between the single-particle ...

Charge transition levels of dangling bonds in III-V semiconductors (AlAs, GaAs, and InAs) are determined via hybrid density-functional calculations. In GaAs, the Ga and As levels are found at 0.28 eV below the conduction band and at 0.16 eV above the valen ...

Defect levels of dangling bonds in germanium are calculated through the use of hybrid density functionals. The theoretical approach is first validated through the consideration of the well-characterized defect levels of the dangling bond in silicon, for wh ...

The fundamental band gaps of liquid water and hexagonal ice are calculated through advanced electronicstructure methods. We compare specifically the performance of state-of-the-art GW calculations with nonempirical hybrid functionals. For the latter, we fi ...

The adsorption of atomic H above the carbon buffer layer in the graphene/SiC(0001) interface system is investigated within density functional theory through a set of realistic interface models that do not impose large artificial strains on the graphene. We ...

A density-functional scheme for the calculation of Raman spectra of disordered materials was developed. Applied to vitreous silica, it was found that the HH Raman spectrum is strongly sensitive to intermediate range order.

We studied protons attached to bridging O atoms in the vicinity of the Si(100)-SiO2 interface through density-functional calculations for realistic interface models. These protons do not disrupt the bonding network except in the case of strained SiO bonds for which they lead to the formation of positively charged threefold coordinated Si(3)(+). Defect energies mainly fall within a band of similar to 0.5 eV, which is stabilized by similar to 0.3 eV at the interface, the energies of the Si(3)(+) defects lying

We carry out first-principles calculations of band gaps of cubic inorganic perovskites belonging to the class CsBX3, with B = Pb, Sn and X = Cl, Br, I. We use the quasi particle self-consistent GW method with efficient vertex corrections to calculate the e ...

We have determined equilibrium geometries and electronic properties of neutral and anionic Cu-n (n = 2,9) clusters by means of first principles calculations in which s and d electrons are treated on equal footing. We find that the calculated electronic density of states is inadequate to interpret photoelectron spectra of Cu-n(-) clusters. We obtain good agreement between calculated excitation energies and experimental spectra when we include final states effects.

Using hybrid density functional calculations, we address the structural properties, formation energies, and charge transition levels of a variety of oxygen defects in GaAs. The set of considered defects comprises the bridging O atom in a As-O-Ga configurat ...

We propose the use of an approximate bootstrap exchange-correlation kernel to account for vertex corrections in self-consistent GW calculations. We show that the approximate kernel gives accurate band gaps for a variety of extended systems, including simpl ...

This book investigates the possible ways of improvement by applying more sophisticated electronic structure methods as well as corrections and alternatives to the supercell model. In particular, the merits of hybrid and screened functionals, as well as of ...

We show that the complete set of intermediate states in second-order perturbation expressions can be replaced by a finite number of states, provided the subspace they span contains one effective state, solution of an inhomogeneous equation. It is therefore not necessary that the subspace be complete. The existence of this effective state guides the choice of the basis in approximate calculations. As an example, we apply these considerations to two-photon transition rates in hydrogen.

Copper vanadates have been proposed as promising photoanodes for water-splitting photoelectrochemical cells, but their performance has recently been shown to be severely limited. To understand this behavior, we study the electronic structure and the optica ...

Self-consistent GW calculations with efficient vertex corrections are employed to determine the electronic structure of liquid water. Nuclear quantum effects are taken into account through ab initio path-integral molecular dynamics simulations. We reveal a ...

We investigate the intercalation of hydrogen at the graphene/SiC(0001) interface through atomistic models characterized by very low strains both in the epitaxial graphene and in the SiC substrate. Adsorption of H at the interface is always stable but shows ...

Alfredo Pasquarello

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1st Principles Molecular-Dynamics Calculation of the Structure and Acidity of a Bulk Zeolite

Cu++ and Li+ interaction with polyethylene oxide by ab initio molecular dynamics

Supported nanoclusters: Preadsorbates tuning catalytic activity

Band alignments and defect levels in Si-HfO2 gate stacks: Oxygen vacancy and Fermi-level pinning

Redox Levels through Constant Fermi-Level ab Initio Molecular Dynamics

Dangling bond charge transition levels in AlAs, GaAs, and InAs

Defect levels of the Ge dangling bond defect

Band gaps of liquid water and hexagonal ice through advanced electronic-structure calculations

First-principles study of H adsorption on graphene/SiC(0001)

Concentration of small ring structures in vitreous silica from a first-principles analysis of the Raman spectrum

Protons at the Si-SiO2 interface: a first principle investigation

Predictive Determination of Band Gaps of Inorganic Halide Perovskites

First Principles Study of Photoelectron-Spectra of Cu-N(-) Clusters

Oxygen defects in GaAs: A hybrid functional study

Accurate band gaps of extended systems via efficient vertex corrections in GW

Advanced Calculations for Defects in Materials: Electronic Structure Methods

Effective-State Approach to 2nd-Order Perturbation-Theory

Sizable Excitonic Effects Undermining the Photocatalytic Efficiency of beta-Cu2V2O7

Ab initio Electronic Structure of Liquid Water

Intercalation of H at the graphene/SiC(0001) interface: Structure and stability from first principles