Publications (22)36.71 Total impact
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Article: Ab-initio angle and energy resolved photoelectron spectroscopy with time-dependent density-functional theory
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ABSTRACT: We present a time-dependent density-functional method able to describe the photoelectron spectrum of atoms and molecules when excited by laser pulses. This computationally feasible scheme is based on a geometrical partitioning that efficiently gives access to photoelectron spectroscopy in time-dependent density-functional calculations. By using a geometrical approach, we provide a simple description of momentum-resolved photoe- mission including multi-photon effects. The approach is validated by comparison with results in the literature and exact calculations. Furthermore, we present numerical photoelectron angular distributions for randomly oriented nitrogen molecules in a short near infrared intense laser pulse and helium-(I) angular spectra for aligned carbon monoxide and benzene.06/2012; -
Article: Ab-initio Computation of Superconducting Properties of Elemental Superconductors and MgB2
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ABSTRACT: We present ab-initio predictions of superconducting properties of some elemental superconductors and of MgB2, based on the Super-Conducting Density Functional theory (SC-DFT). This formalism allows a description of superconducting properties at thermal equilibrium by means of three “densities”: the ordinary electron density, the superconducting order parameter, and the diagonal of the nuclear N-body density matrix. These quantities are determined through self-consistent solutions of Bogoliubov-de Gennes Kohn-Sham like equations, involving exchange-correlation potentials which are universal functionals of the three above-mentioned quantities. By means of approximate expressions for the relevant functionals, we obtain an ab-initio description of the superconducting state, completely free of empirical parameters. The results of our present implementation of SC-DFT for selected materials are discussed in terms of superconducting energy gap, critical temperature and specific heat, and compared with experiments. KEY WORDS: Ab-initio computation–superconducting density functional theory–magnesium diboride.Journal of Superconductivity 04/2012; 18(5):649-652. -
Article: Density functional theory beyond the linear regime: Validating adiabatic LDA
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ABSTRACT: We present a local density approximation (LDA) for one-dimensional (1D) systems interacting via the soft-Coulomb interaction based on quantum Monte-Carlo calculations. Results for the ground-state energies and ionization potentials of finite 1D systems show excellent agreement with exact calculations, obtained by exploiting the mapping of an $N$-electron system in $d$ dimensions, onto a single electron in $N\times d$ dimensions properly symmetrized by the Young diagrams. We conclude that 1D LDA is of the same quality as its three-dimensional (3D) counterpart, and we infer conclusions about 3D LDA. The linear and non-linear time-dependent responses of 1D model systems using LDA, exact exchange, and the exact solution are investigated and show very good agreement in both cases, except for the well known problem of missing double excitations. Consequently, the 3D LDA is expected to be of good quality beyond linear response. In addition, the 1D LDA should prove useful in modeling the interaction of atoms with strong laser fields, where this specific 1D model is often used.01/2011; -
Article: Density-Matrix-Power Functional: Performance for Finite Systems and the Homogeneous Electron Gas
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ABSTRACT: An exchange correlation energy functional involving fractional power of the one-body reduced density matrix [Phys. Rev. B {\bf 78}, 201103 (2008)] is applied to finite systems and to the homogeneous electron gas. The performance of the functional is assessed for the correlation and atomization energies of the molecules contained in the G2 set and for the correlation energy of the homogeneous electron gas. High accuracy is found for these two very different types of systems.01/2009; -
Article: Cluster-surface and cluster-cluster interactions: Ab initio calculations and modeling of asymptotic van der Waals forces
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ABSTRACT: We present fully ab initio calculations of van der Waals coefficients for two different situations: (i) the interaction between hydrogenated silicon clusters and (ii) the interactions between these nanostructures and a nonmetallic surface (a silicon or a silicon carbide surface). The methods used are very efficient and allow the calculation of systems containing hundreds of atoms. The results obtained are further analyzed and understood with the help of simple models. These models can be of interest for molecular-dynamics simulations of silicon nanostructures on surfaces, where they can give a very fast yet sufficiently accurate determination of the van der Waals interaction at large separations.Physical Review B 07/2008; 78(3):035333. · 3.69 Impact Factor -
Article: Specification of an extensible and portable file format for electronic structure and crystallographic data
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ABSTRACT: In order to allow different software applications, in constant evolution, to interact and exchange data, flexible file formats are needed. A file format specification for different types of content has been elaborated to allow communication of data for the software developed within the European Network of Excellence "NANOQUANTA", focusing on first-principles calculations of materials and nanosystems. It might be used by other software as well, and is described here in detail. The format relies on the NetCDF binary input/output library, already used in many different scientific communities, that provides flexibility as well as portability accross languages and platforms. Thanks to NetCDF, the content can be accessed by keywords, ensuring the file format is extensible and backward compatible.06/2008; -
Article: Octopus: a tool for the application of time-dependent density functional theory
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ABSTRACT: We report on the background, current status, and current lines of development of the octopus project. This program materializes the main equations of density-functional theory in the ground state, and of time-dependent density-functional theory for dynamical effects. The focus is nowadays placed on the optical (i.e. electronic) linear response properties of nanostructures and biomolecules, and on the non-linear response to high-intensity fields of finite systems, with particular attention to the coupled ionic-electronic motion (i.e. photo-chemical processes). In addition, we are currently extending the code to the treatment of periodic systems (both to one-dimensional chains, two-dimensional slabs, or fully periodic solids), magnetic properties (ground state properties and excitations), and to the field of quantum-mechanical transport or “molecular electronics.” In this communication, we concentrate on the development of the methodology: we review the essential numerical schemes used in the code, and report on the most recent implementations, with special attention to the introduction of adaptive coordinates, to the extension of our real-space technique to tackle periodic systems, and on large-scale parallelization. More information on the code, as well as the code itself, can be found at http://www.tddft.org/programs/octopus/.physica status solidi (b) 06/2006; 243(11):2465–2488. · 1.32 Impact Factor -
Article: Superconductivity in lithium, potassium, and aluminum under extreme pressure: a first-principles study.
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ABSTRACT: Extreme pressure strongly affects the superconducting properties of "simple" elemental metals, such as Li, K, and Al. Pressure induces superconductivity in Li (as high as 17 K) while suppressing it in Al. We report first-principles investigations of the superconducting properties of dense Li, K, and Al based on a recently proposed, parameter-free, method. Our results show an unprecedented agreement with experiments, assess the predictive power of the method over a wide range of densities and electron-phonon couplings, and provide predictions for K, where no experiments exist so far. More importantly, our results help uncover the physics of the different behaviors of Li and Al in terms of phonon softening and Fermi surface nesting in Li.Physical Review Letters 03/2006; 96(4):047003. · 7.37 Impact Factor -
Book: Time-Dependent Density Functional Theory, Lecture Notes Phys. 706
edited by M. A. L. Marques and C. A. Ulrich and F. Nagueira and A. Rubio and K. Burke and E. K. U. Gross, 01/2006; Springer. -
Article: Octopus: a Tool for the Application of Time-dependent Density Functional Theory
Physica Status Solidi: Towards Atomistic Materials Design. 01/2006; 243:2465 - 2488. -
Article: Superconductivity in lithium, potassium and aluminium under extreme pressure: A first-principles study
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ABSTRACT: Extreme pressure strongly affects the superconducting properties of ``simple'' elemental metals, like Li, K and Al. Pressure induces superconductivity in Li (as high as 17 K), while suppressing it in Al. We report first-principles investigations of the superconducting properties of dense Li, K and Al based on a recently proposed, parameter-free, method. Our results show an unprecedented agreement with experiments, assess the predictive power of the method over a wide range of densities and electron-phonon couplings, and provide predictions for K, where no experiments exist so far. More importantly, our results help uncovering the physics of the different behaviors of Li and Al in terms of phonon softening and Fermi surface nesting in Li. Comment: 4 pages, 4 figures10/2005; -
Article: Superconducting properties of MgB2 from first principles.
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ABSTRACT: Solid MgB(2) has rather interesting and technologically important properties, such as a very high superconducting transition temperature. Focusing on this compound, we report the first nontrivial application of a novel density-functional-type theory for superconductors, recently proposed by the authors. Without invoking any adjustable parameters, we obtain the transition temperature, the gaps, and the specific heat of MgB(2) in very good agreement with experiment. Moreover, our calculations show how the Coulomb interaction acts differently on sigma and pi states, thereby stabilizing the observed superconducting phase.Physical Review Letters 02/2005; 94(3):037004. · 7.37 Impact Factor -
Article: Ab-initio theory of superconductivity - I: Density functional formalism and approximate functionals
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ABSTRACT: A novel approach to the description of superconductors in thermal equilibrium is developed within a formally exact density-functional framework. The theory is formulated in terms of three ``densities'': the ordinary electron density, the superconducting order parameter, and the diagonal of the nuclear N-body density matrix. The electron density and the order parameter are determined by Kohn-Sham equations that resemble the Bogoliubov-de Gennes equations. The nuclear density matrix follows from a Schroedinger equation with an effective N-body interaction. These equations are coupled to each other via exchange-correlation potentials which are universal functionals of the three densities. Approximations of these exchange-correlation functionals are derived using the diagrammatic techniques of many-body perturbation theory. The bare Coulomb repulsion between the electrons and the electron-phonon interaction enter this perturbative treatment on the same footing. In this way, a truly ab-initio description is achieved which does not contain any empirical parameters.10/2004; -
Article: Ab-initio theory of superconductivity - II: Applications to elemental metals
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ABSTRACT: The density functional theory for superconductors developed in the preceding article [cond-mat/0408685] is applied to the calculation of superconducting properties of several elemental metals. In particular, we present results for the transition temperature, for the gap at zero temperature, and for thermodynamic properties like the specific heat. We obtain an unprecedented agreement with experimental results. Superconductors both with strong and weak electron-phonon coupling are equally well described. This demonstrates that, as far as conventional superconductivity is concerned, the first-principles prediction of superconducting properties is feasible. Comment: 12 pages, 10 figures, 3 tables, revised version08/2004; -
Article: Time-dependent density functional theory.
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ABSTRACT: Time-dependent density functional theory (TDDFT) can be viewed as an exact reformulation of time-dependent quantum mechanics, where the fundamental variable is no longer the many-body wave function but the density. This time-dependent density is determined by solving an auxiliary set of noninteracting Schrodinger equations, the Kohn-Sham equations. The nontrivial part of the many-body interaction is contained in the so-called exchange-correlation potential, for which reasonably good approximations exist. Within TDDFT two regimes can be distinguished: (a) If the external time-dependent potential is "small," the complete numerical solution of the time-dependent Kohn-Sham equations can be avoided by the use of linear response theory. This is the case, e.g., for the calculation of photoabsorption spectra. (b) For a "strong" external potential, a full solution of the time-dependent Kohn-Sham equations is in order. This situation is encountered, for instance, when matter interacts with intense laser fields. In this review we give an overview of TDDFT from its theoretical foundations to several applications both in the linear and in the nonlinear regime.Annual Review of Physical Chemistry 02/2004; 55:427-55. · 14.13 Impact Factor -
Article: Excited states dynamics in time-dependent density functional theory
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ABSTRACT: We present numerical simulations of femtosecond laser induced dynamics of some selected simple molecules -- hydrogen, singly ionized sodium dimer, singly ionized helium trimer and lithium cyanide. The simulations were performed within a real-space, real-time, implementation of time-dependent density functional theory (TDDFT). High harmonic generation, Coulomb explosion and laser induced photo-dissociation are observed. The scheme also describes non-adiabatic effects, such as the appearance of even harmonics for homopolar but isotopically asymmetric dimers, even if the ions are treated classically. This TDDFT-based method is reliable, scalable, and extensible to other phenomena such as photoisomerization, molecular transport and chemical reactivity.The European Physical Journal D 01/2004; 28(2):211-218. · 1.48 Impact Factor -
Article: TIME-DEPENDENT DENSITY FUNCTIONAL THEORY
Annu. Rev. Phys. Chem. 01/2004; 55. -
Article: Density functional theory for superconductors
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ABSTRACT: Two recently proposed exchange-correlation functionals describing the superconducting phase of matter are reviewed and further explored: Whereas the first is a generalization of the local density approximation dealing with purely electronic correlations, the second is a functional derived from Kohn–Sham perturbation theory that includes electronic and phononic correlations on the same footing. Superconducting properties of simple metals obtained with the latter functional agree rather well with experimental results. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004International Journal of Quantum Chemistry 12/2003; 99(5):790 - 797. · 1.36 Impact Factor -
Article: Relativistic Theory of Superconductivity
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ABSTRACT: The relativistic generalization of the theory of superconductivity is reviewed with respect to its conceptual basis and first applications. The construction of relativistically covariant order parameters for superconductors is outlined and the generalization of the Dirac equation for the superconducting state is presented. A weakly relativistic expansion of this equation leads to the Pauli equation for superconductors, which describes the lowest-order relativistic corrections to the conventional theory of superconductivity. The physics of these corrections is discussed, and the prospects for experimental detection of relativistic effects in superconductors are examined.02/2001; -
Article: Superconducting properties of MgB2 from first principles
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ABSTRACT: The discovery of superconductivity in MgB2, with a rather high transition temperature, has triggered a large number of theoretical and experimental investigations on important issues such as, e.g., the role of gap anisotropy over the Fermi surface (multi-gap superconductivity). We report here the results obtained in this compound using the density functional theory for superconductors, recently proposed by the authors. Without invoking any adjustable parameters, such as μ∗, we obtain the transition temperature, the gaps, and the specific heat in very good agreement with experiment. Moreover, our calculations allow for a detailed study of how the phonon-mediated attraction and Coulomb repulsion act differently on σ and π states, thereby stabilizing the observed superconducting phase.Physica C: Superconductivity.
Top co-authors
Top Journals
Institutions
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2012
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French National Centre for Scientific Research
Lyon, Rhone-Alpes, France
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2006
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University of Coimbra
- Departamento de Física
Coimbra, Distrito de Coimbra, Portugal
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2003–2005
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Freie Universität Berlin
- • Institute of Theoretical Physics
- • Department of Physics
Berlin, Land Berlin, Germany -
Universidad del País Vasco / Euskal Herriko Unibertsitatea
Leioa, Basque Country, Spain
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2004
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Universität Würzburg
- Department of Theoretical and Astrophysics
Würzburg, Bavaria, Germany
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