Publications de Audrius Alkauskas

Dynamic structure factors of Cu, Ag, and Au: Comparative study from first principles

Simon Schneider, Audrius Alkauskas, Cécile Hébert

We present a comparative theoretical and experimental study of dynamic structure factors (momentum-dependent loss functions) of the noble metals Cu, Ag, and Au in the energy range of 0-60 eV. The emphasis is on theoretical results that are compared with ne ...

Amer Physical Soc2013

Defect levels of carbon-related defects at the SiC/SiO2 interface from hybrid functionals

Alfredo Pasquarello, Fabien Devynck, Peter Broqvist, Audrius Alkauskas

We investigate carbon single-atom and pair defects at the SiC/SiO2 interface as candidate defects for the density of defect states in the SiC band gap. In order to accurately describe the electronic defect levels with respect to the SiC band edges, we use ...

2011

Charge transition levels of carbon-, oxygen-, and hydrogen-related defects at the SiC/SiO2 interface through hybrid functionals

Alfredo Pasquarello, Fabien Devynck, Peter Broqvist, Audrius Alkauskas

We calculate charge transition levels of various defects at the SiC/SiO2 interface within a scheme based on hybrid density functionals, which accurately reproduce the involved band gaps and band offsets. The defect levels are first evaluated in bulk models ...

2011

Band-edge problem in the theoretical determination of defect energy levels: The O vacancy in ZnO as a benchmark case

Alfredo Pasquarello, Audrius Alkauskas

Calculations of formation energies and charge transition levels of defects routinely rely on density functional theory (DFT) for describing the electronic structure. Since bulk band gaps of semiconductors and insulators are not well described in semilocal ...

2011

Advanced Calculations for Defects in Materials: Electronic Structure Methods

Alfredo Pasquarello, Audrius Alkauskas

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 ...

Wiley-VCH2011

Capturing EELS in the reciprocal space

Audrius Alkauskas, Cécile Hébert

In this work two aspects of momentum-dependent electron energy loss spectrometry are studied, both in the core-loss and in the low-loss region. In the case of core losses, we focus on the demonstration and the interpretation of an unexpected non-Lorentzian ...

2011

Defect levels through hybrid density functionals: Insights and applications

Alfredo Pasquarello, Peter Broqvist, Audrius Alkauskas

Hybrid density functional calculations applied to defect charge transition levels are explored in the attempt to overcome the band-gap problem of semilocal density functionals. Charge transition levels of a large set of point defects calculated with semilo ...

2011

Theoretical analysis of the momentum-dependent loss function of bulk Ag

Simon Schneider, Audrius Alkauskas, Cécile Hébert

We analyze the momentum-dependent loss function of bulk silver, calculated via the random-phase approximation and based on the band structure from semi-local density functional theory calculations. In the energy range of 0-55 eV the spectrum reveals the ex ...

Elsevier2010

Energy levels of candidate defects at interfaces SiC/SiO2 interfaces

Alfredo Pasquarello, Fabien Devynck, Peter Broqvist, Audrius Alkauskas

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 ...

2010

Hybrid-functional calculations with plane-wave basis sets: Effect of singularity correction on total energies, energy eigenvalues, and defect energy levels

Alfredo Pasquarello, Peter Broqvist, Audrius Alkauskas

When described through a plane-wave basis set, the inclusion of exact nonlocal exchange in hybrid functionals gives rise to a singularity, which slows down the convergence with the density of sampled k points in reciprocal space. In this work, we investiga ...

2009

First principles investigation of defect energy levels at semiconductor-oxide interfaces: Oxygen vacancies and hydrogen interstitials in the Si-SiO2-HfO2 stack

Alfredo Pasquarello, Peter Broqvist, Audrius Alkauskas

We introduce a scheme for the calculation of band offsets and defect energy levels at semiconductor-oxide interfaces. Our scheme is based on the use of realistic atomistic models of the interface structure and of hybrid functionals for the evaluation of th ...

American Institute of Physics2009

Li-related defects in ZnO : hybrid functional calculations

Nava Setter, Alexander Tagantsev, Alfredo Pasquarello, Audrius Alkauskas, Alexandra Sarabando de Carvalho

Hybrid density functional calculations are used to model substitutional lithium (LiZn) and interstitial lithium (Lii) defects in ZnO. The calculated transition levels and formation energies are compared to those obtained using a semilocal density functiona ...

2009

Alignment of defect energy levels at the Si-SIO2 interface from hybrid density functional calculations

Alfredo Pasquarello, Peter Broqvist, Audrius Alkauskas

2010

Defect levels of the Ge dangling bond defect

Alfredo Pasquarello, Peter Broqvist, Audrius Alkauskas

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 ...

2010

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

Nava Setter, Alexander Tagantsev, Alfredo Pasquarello, Audrius Alkauskas, Alexandra Sarabando de Carvalho

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 ...

2009

Charge state of the O-2 molecule during silicon oxidation through hybrid functional calculations

Alfredo Pasquarello, Peter Broqvist, Audrius Alkauskas

We study the charge state of the diffusing O-2 molecule during silicon oxidation through hybrid functional calculations. We calculate charge-transition levels of O-2 in bulk SiO2 and use theoretical band offsets to align these levels with respect to the Si ...

2008

Charge transition levels of the Ge dangling bond defect at Ge/insulator interfaces

Alfredo Pasquarello, Peter Broqvist, Audrius Alkauskas

We calculate defect levels of dangling bonds in germanium using hybrid density functionals. To validate our approach, we first consider the dangling bond in silicon finding two well-separated defect levels, in excellent correspondence with their experiment ...

2008

Defect levels of dangling bonds in silicon and germanium through hybrid functionals

Alfredo Pasquarello, Peter Broqvist, Audrius Alkauskas

Defect levels of dangling bonds in silicon and germanium are determined within their respective band gaps through the use of hybrid density functionals. To validate our approach, we first considered the dangling bond in silicon finding two well-separated d ...

2008

Defect energy levels in density functional calculations: Alignment and band gap problem

Alfredo Pasquarello, Peter Broqvist, Audrius Alkauskas

For materials of varying band gap, we compare energy levels of atomically localized defects calculated within a semilocal and a hybrid density-functional scheme. Since the latter scheme partially relieves the band gap problem, our study describes how calcu ...

2008

Band offsets at semiconductor-oxide interfaces from hybrid density-functional calculations

Alfredo Pasquarello, Fabien Devynck, Peter Broqvist, Audrius Alkauskas

Band offsets at semiconductor-oxide interfaces are determined through a scheme based on hybrid density functionals, which incorporate a fraction alpha of Hartree-Fock exchange. For each bulk component, the fraction alpha is tuned to reproduce the experimen ...

2008