First-principles calculation of the electronic, dielectric, and dynamical properties of CaF2

in Physical Review. B : Condensed Matter (2003), 68

First-principles calculations of the nonlinear optical susceptibilities and Raman scattering spectra of lithium niobate

in Journal of Physics : Condensed Matter (2007), 19(45),

Nonlinear optical susceptibilities and nonresonant Raman scattering spectra of the ferroelectric phase of lithium niobate (LiNbO3) are computed using a first-principles approach based on density ... [more ▼]

Nonlinear optical susceptibilities and nonresonant Raman scattering spectra of the ferroelectric phase of lithium niobate (LiNbO3) are computed using a first-principles approach based on density functional theory and taking advantage of a recent implementation based on the nonlinear response formalism and the 2n+1 theorem. Infrared reflectivity spectra of the ferroelectric phase of LiNbO3 are also calculated. New assignments are proposed for the E-modes, clarifying a longstanding debate in the literature. In addition, it is shown that knowledge of the nonlinear optical susceptibility tensor of LiNbO3 does not significantly alter the profile of its Raman spectra in a configuration where the longitudinal optic modes are involved. [less ▲]

First-Principles Calculations of Thermodynamic Properties and Pressure- Induced Phase Transitions in Ga2O3 and Al2O3

Conference (2007, March)

First-principles computation of material properties: the ABINIT software project

in Computational Materials Science (2002), 25(3), 478-492

The density functional theory (DFT) computation of electronic structure, total energy and other properties of materials, is a field in constant progress. In order to stay at the forefront of knowledge, a ... [more ▼]

The density functional theory (DFT) computation of electronic structure, total energy and other properties of materials, is a field in constant progress. In order to stay at the forefront of knowledge, a DFT software project can benefit enormously from widespread collaboration, if handled properly. Also, modern software engineering concepts can considerably ease its development. The ABINIT project relies upon these ideas: freedom of sources, reliability, portability, and self-documentation are emphasised, in the development of a sophisticated plane-wave pseudopotential code. We describe ABINITv3.0, distributed under the GNU General Public License. The list of ABINITv3.0 capabilities is presented, as well as the different software techniques that have been used until now: PERL scripts and CPP directives treat a unique set of FORTRAN90 source files to generate sequential (or parallel) object code for many different platforms; more than 200 automated tests secure existing capabilities; strict coding rules are followed; the documentation is extensive, including online help files, tutorials, and HTML-formatted sources. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

First-principles computation of material properties: the ABINIT software project.

in Computational Materials Science (2002), 25

First-principles design of efficient solar cells using two-dimensional arrays of core-shell and layered SiGe nanowires

in Physical Review. B, Condensed Matter and Materials Physics (2011), 83(3), 0353176-03531760353176

Research for third generation solar cell technology has been driven by the need to overcome the efficiency and cost problems encountered by current crystalline Si- and thin-film-based solar cells. Using ... [more ▼]

Research for third generation solar cell technology has been driven by the need to overcome the efficiency and cost problems encountered by current crystalline Si- and thin-film-based solar cells. Using first-principles methods, Ge/Si and Si/Ge core/shell and Si-Ge layered nanowires are shown to possess the required qualities for an efficient use in photovoltaic applications. We investigate the details of their band structure, effective mass, absorption property, and charge-carrier localization. The strong charge separation and improved absorption in the visible spectrum indicate a remarkable quantum efficiency that, combined with new designs, compares positively with bulk Si. [less ▲]

First-principles modeling of the thermoelectric properties of SrTiO3/SrRuO3 superlattices

in Physical Review. B, Condensed Matter and Materials Physics (2012), 86

Using a combination of first-principles simulations, based on density functional theory and Boltzmann’s semiclassical theory, we have calculated the transport and thermoelectric properties of the half ... [more ▼]

Using a combination of first-principles simulations, based on density functional theory and Boltzmann’s semiclassical theory, we have calculated the transport and thermoelectric properties of the half-metallic twodimensional electron gas confined in single SrRuO3 layers of SrTiO3/SrRuO3 periodic superlattices. Close to the Fermi energy, we find that the semiconducting majority-spin channel displays a very large in-plane component of the Seebeck tensor at room temperature, S ∼ 1500 μV/K, and the minority-spin channel shows good in-plane conductivity, σ = 2.5 (m cm)−1. However, we find that the total power factor and thermoelectric figure of merit for reduced doping is too small for practical applications. Our results support that the confinement of the electronic motion is not the only thing that matters to describe the main features of the transport and thermoelectric properties with respect the chemical doping, but the shape of the electronic density of states, which in our case departs from the free-electron behavior, is also important. The evolution of the electronic structure, electrical conductivity, Seebeck coefficient, and power factor as a function of the chemical potential is explained by a simplified tight-binding model. We find that the electron gas in our system is composed by a pair of one-dimensional electron gases orthogonal to each other. This reflects the fact the physical dimensionality of the electronic system (1D) can be even smaller than that of the spacial confinement of the carriers (2D). [less ▲]

First-principles studies of ferroelectric oxides

in Physics of Ferroelectrics: A Modern Perspective (2007)

The application of first-principles methods to the study of ferroelectric oxides is reviewed. While the main focus is on the perovskites, particularly the most-studied compounds BaTiO3, PbTiO3, and SrTiO3 ... [more ▼]

The application of first-principles methods to the study of ferroelectric oxides is reviewed. While the main focus is on the perovskites, particularly the most-studied compounds BaTiO3, PbTiO3, and SrTiO3, other oxide families, including LiNbO3, layered perovskites, nitrites and nitrates, and electronic and magnetic ferroelectrics, are included. Results are presented for crystal structure, polarization and dielectric and piezoelectric coefficients. The identification of lattice instabilities through the computation of phonon dispersion relations for a high-symmetry reference phase is presented. Results at nonzero temperature, obtained through effective Hamiltonian and interatomic potential approaches, are given. Calculations for solid solutions, defects, thin films, superlattices and nanostructures are described. Challenges and prospects for future research are identified. [less ▲]

First-principles study of barium titanate under hydrostatic pressure

in Physical Review B (2006), 74(18),

The behavior of the ferroelectric instability of cubic barium titanate under increasing hydrostatic pressure is investigated from first principles. Beyond a rapid suppression and then reappearance of this ... [more ▼]

The behavior of the ferroelectric instability of cubic barium titanate under increasing hydrostatic pressure is investigated from first principles. Beyond a rapid suppression and then reappearance of this instability at about 140 GPa, we highlight a sudden change in the dynamical behavior of BaTiO3 at a pressure of approximate to 20 GPa. We show that the ferroelectric instability at high pressure has a totally different character than at atmospheric pressure. From the analysis of the interatomic force constants, we demonstrate that the destabilizing role of the short-range forces at high pressure must be related to the change of the soft mode eigenvector rather than to an original electronic effect. [less ▲]

First-Principles Study of Electron-Phonon Coupling in STO and 2DEG

Conference (2011, May)