Publications by Alfredo Pasquarello

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A new formulation of the current within the London approximation allows the calculation of ring currents in topologically complex molecules. Application of this theory to C60 demonstrates the existence of remarkable pi-electron ring currents. Paramagnetic currents, in size comparable to the ones in benzene, flow within the pentagons, whereas weaker diamagnetic currents flow all around the C60 molecule. The overall vanishing ring-current magnetic susceptibility results from a cancellation of diamagnetic and

Using constrained ab initio molecular dynamics, we investigate the reaction of the O-2 molecule at the Si(100)-SiO2 interface during Si oxidation. The reaction proceeds sequentially through the incorporation of the O-2 molecule in a Si-Si bond and the dissociation of the resulting network O-2 species. The oxidation reaction occurs nearly spontaneously and is exothermic, irrespective of the O-2 spin state or of the amount of excess negative charge available at the interface. The reaction evolves through the

A magneto-optical study of accepters in varying degrees of confinement in GaAs/Al-x Ga-l-x, As quantum wells (QW's) is presented. A model for the splitting of the acceptor bound exciton (BE) and the allowed BE transitions in the presence of a magnetic field is presented. Our experimental results for the acceptor BE emission agree with calculated g values for bound holes, e.g., g(3/2) = 0. 61 and g(1/2) = 0.35 for a 150-Angstrom-wide QW. Furthermore, the energy separation between the acceptor m(j) = +/-3/2 1

We extend the quasiparticle self-consistent approach beyond the GW approximation by using a range separated vertex function. The developed approach yields band gaps, dielectric constants, and band positions with an accuracy similar to highest-level electro ...

We investigate the absorption spectra of the

F

centers in MgO and CaO using material-specific hybrid functionals combined with time-dependent hybrid-functional theory calculations. Our study accounts for electron-hole interaction, zero-phonon renormalization, and finite-size effects, which are all found to contribute to the achieved accuracy. The spectra of the neutral states solely present absorption lines stemming from internal defect-to-defect transitions without involving conduction band states of the

Arsenic 2p core-level shifts at GaAs/Al2O3 interfaces are determined with respect to bulk GaAs through density functional calculations. Atomistic interface models are constructed in which As atoms are found in various chemical environments. Both Ga-termina ...

Band offsets of the Ge/GeO2 interface are calculated through a hybrid density functional scheme. We first generate a model of disordered GeO2 through ab initio molecular dynamics to describe the oxide component. For addressing the interface, we then consider an atomistic model in which amorphous GeO2 is connected to crystalline Ge through a suboxide transition region showing regular structural parameters. The band offsets are obtained through the application of an alignment scheme, which reproduces the expe

Partial molar volumes of ions in water solution are calculated through pressures obtained from ab initio molecular dynamics simulations. The correct definition of pressure in charged systems subject to periodic boundary conditions requires access to the va ...

We determine energy levels of candidate defects for the high defect density observed just below the SiC conduction band at SiC/SiO 2 interfaces. We address C interstitials and H bridge defects which both show defect levels in the upper part of the SiC band ...

A model interface between Si and disordered SiO2 is obtained which incorporates the interface bonding pattern previously generated by first-principles molecular dynamics. The model is then characterized by comparing its properties with experimental data which provide an atomic-scale characterization of the interfacial region. The model is found to adequately reproduce the disordered nature of the oxide, the good coordination at the interface, the transition to stoichiometric SiO2, and the photoemission data

We calculate the Raman spectra of vitreous SiO 2 , vitreous GeO 2 , and vitreous GeSe 2 within a density functional scheme. Due to the sensitivity of the Raman spectra to correlations extending beyond the tetrahedral unit, we extract through the comparison ...

We calculate the transverse and the longitudinal infrared absorption spectra of the hydrated silicon surface using a first-principles approach. The absorption spectra are computed for two different configurations of water molecules dissociatively chemisorbed on the Si(100)-(2 X 1) surface at full coverage. Our calculations compare favorably with the experimental spectra for both the frequency and the intensity of the absorption peaks. Our results suggest the possibility of combining infrared spectroscopy an

We employ constant-Fermi-level ab initio molecular dynamics to investigate defects at the InGaAs/oxide interface upon inversion. We adopt a substoichiometric amorphous model for modelling the structure at the interface and investigate the formation of defect structures upon setting the Fermi-level above the conduction band minimum. The defect formation is detected through both an analysis of the atomic structure and a Wannier-decomposition of the electronic structure. This computer driven approach is able t

We modeled liquid oxygen using ab initio molecular dynamics in which both the atomic structure and the noncollinear magnetic structure evolve without constraints. The atomic structure shows preference for parallel alignment of first-neighbor molecules and is supported by an excellent agreement between theoretical and experimental nuclear structure factors. The magnetic structure shows short-range antiferromagnetic correlations in agreement with spin-polarized neutron diffraction data. The observed correlati

Extensive machine-learning-assisted research has been dedicated to predicting band gaps for perovskites, driven by their immense potential in photovoltaics. Yet, the effectiveness is often hampered by the lack of high-quality band gap data sets, particularly for perovskites involving d orbitals. In this work, we consistently calculate a large data set of band gaps with a high level of accuracy, which is rigorously validated by experimental and state-of-the-art GW band gaps. Leveraging this achievement, our

Charge transition levels of the As-As dimer defect at the InGaAs/Al2O3 interface are determined through density-functional calculations. At variance with the GaAs/Al2O3 interface where this defect gives rise to states within the band gap, its defect levels ...

Semilocal density functionals such as the Perdew-Burke-Ernzerhof (PBE) functional substantially underestimate experimental band gaps. Hybrid functionals address this band gap problem by admixing a fraction of Fock exchange to semilocal exchange. The optimal mixing parameter depends on the specific material and can be identified as the inverse dielectric constant (dielectric-dependent hybrid functional, DDH). Here, we show that dielectric constants obtained using the r 2 SCAN meta-GGA functional are signific

We study the dielectric susceptibility of liquid hydrogen chloride at a temperature of 313 K using ab initio molecular dynamics evolving, in a homogeneous electric field. For an evolution in absence of electric field, the calculated neutron structure factor shows good agreement with the experimental one, supporting the structural properties of our model. We obtain the real and imaginary parts of the dielectric susceptibility as a function of frequency from the evolution of the polarization upon the onset of

The O center substitutional to As (O-As) is addressed through hybrid functional calculations as a candidate defect to explain the Fermi-level pinning in oxygen-doped GaAs. The defect center shows amphoteric behavior which could lead to Fermi-level pinning. ...

We determine the transition levels of electron and hole polarons at the BiVO4-water interface through thermodynamic integration within a hybrid functional scheme, thereby accounting for the liquid nature of the water component. The electron polaron is foun ...

Alfredo Pasquarello

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Ring Currents in Icosahedral C60

Reaction of the oxygen molecule at the Si(100)-SiO2 interface during silicon oxidation

Magnetooptical Studies of Acceptors Confined in Gaas/Alxga1-Xas Quantum-Wells

Vertex function compliant with the Ward identity for quasiparticle self-consistent calculations beyond GW

Absorption lines of 𝐹 centers in MgO and CaO through time-dependent hybrid-functional theory calculations

First principles study of As 2p core-level shifts at GaAs/Al2O3 interfaces

Band offsets at the Ge/GeO2 interface through hybrid density functionals

Partial Molar Volumes of Aqua Ions from First Principles

Energy levels of candidate defects at interfaces SiC/SiO2 interfaces

Model interface between silicon and disordered SiO2

Medium range structure of tetrahedrally-bonded glasses through the first principles investigation of Raman spectra

First-principles theory of infrared absorption spectra at surfaces and interfaces: Application to the Si(100): H2O surface

Electron trap states at InGaAs/oxide interfaces under inversion through constant Fermi-level ab initio molecular dynamics

Ab initio molecular dynamics investigation of the structure and the noncollinear magnetism in liquid oxygen: Occurrence of O-4 molecular units

High-Quality Data Enabling Universality of Band Gap Descriptor and Discovery of Photovoltaic Perovskites

Defect energy levels of the As-As dimer at InGaAs/oxide interfaces: A first principles study

Dielectric-dependent hybrid functional based on meta-GGA

Dielectric susceptibility of dipolar molecular liquids by ab initio molecular dynamics: application to liquid HCl

The O-As defect in GaAs: A hybrid density functional study

Electron and Hole Polarons at the BiVO4-Water Interface