Showing papers by "Paolo Giannozzi published in 2005"

First-principles codes for computational crystallography in the Quantum-ESPRESSO package

Abstract: The Quantum-ESPRESSO package is a multipurpose and multi-platform software for ab-initio calculations of condensed matter (periodic and disordered) systems. Codes in the package are based on density functional theory and on a plane wave/pseudopotential description of the electronic ground state and are ideally suited for structural optimizations (both at zero and at finite temperature), linear response calculations (phonons, elastic constants, dielectric and Raman tensors, etc.) and high-temperature molecular dynamics. Examples of applications of the codes included in the package are briefly discussed.

Density-functional perturbation theory

Abstract: The calculation of vibrational properties of materials from their electronic structure is an important goal for materials modeling. A wide variety of physical properties of materials depend on their lattice-dynamical behavior: specific heats, thermal expansion, and heat conduction; phenomena related to the electron‐phonon interaction such as the resistivity of metals, superconductivity, and the temperature dependence of optical spectra, are just a few of them. Moreover, vibrational spectroscopy is a very important tool for the characterization of materials. Vibrational frequencies are routinely and accurately measured mainly using infrared and Raman spectroscopy, as well as inelastic neutron scattering. The resulting vibrational spectra are a sensitive probe of the local bonding and chemical structure. Accurate calculations of frequencies and displacement patterns can thus yield a wealth of information on the atomic and electronic structure of materials. In the Born‐Oppenheimer (adiabatic) approximation, the nuclear motion is determined by the nuclear Hamiltonian H:

Origins of low- and high-pressure discontinuities of $T_{c}$ in niobium

Abstract: merical accuracy We give a few advices for an efficient calculation of the electron-phonon coupling Some of the technical details, however, can be used in general for calculations of other properties which require an accurate numerical integration with the delta function This paper is organized as follows: In the next Section we remind the physical definitions and give some details of the calculation of electron-phonon interaction coefficients using Vanderbilt’s ultrasoft pseudopotentials 10 In Sec III, we give the technical details (Subsec A) and present results for several properties under pressure: the lattice constant and bulk modulus (Subsec B), the band structure and Fermi surface (Subsec C), the phonon frequencies and linewidths (Subsec D), and the Eliashberg function and electron-phonon coupling constant (Subsec E) In Sec IV, we discuss the origin of the anomalies, and we summarize in Sec V In the Appendix, we give numerical details for the calculation of the Eliashberg function

First-Principles Molecular Dynamics

Abstract: Ab initio or first-principles methods have emerged in the last two decades as a powerful tool to probe the properties of matter at the microscopic scale. These approaches are used to derive macroscopic observables under the controlled condition of a “computational experiment,” and with a predictive power rooted in the quantum-mechanical description of interacting atoms and electrons. Density-functional theory (DFT) has become de facto the method of choice for most applications, due to its combination of reasonable scaling with system size and good accuracy in reproducing most ground state properties. Such an electronic-structure approach can then be combined with classical molecular dynamics to provide an accurate description of thermodynamic properties and phase stability, atomic dynamics, and chemical reactions, or as a tool to sample the features of a potential energy surface.

Electron correlation effects on the hydrogen passivation of Mn x Ga 1-x As dilute magnetic semiconductors

Abstract: Atomic hydrogen diffuses in semiconductor lattices and binds to impurities by forming complexes that can lead to a full neutralization of the impurity effects. In the present paper, the structural, vibrational, electronic, and magnetic properties of complexes formed by H in the ${\mathrm{Mn}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ $(x=0.03)$ dilute magnetic semiconductor have been investigated by using first-principles density-functional theory theoretical methods both in gradient-corrected spin-density ($\ensuremath{\sigma}$-GGA) and Hubbard $U(\ensuremath{\sigma}\text{\ensuremath{-}}\mathrm{GGA}+U)$ approximations. The results account for recent experimental findings showing a H passivation of the electronic and magnetic properties of Mn in GaAs. Most importantly, they show that electron correlation has crucial effects on the properties of H-Mn complexes.

Vibrational properties of DsRed model chromophores.

Abstract: We calculate the vibrational properties for models of the chromophore of DsRed – a recently cloned fluorescent protein emitting red light. The calculations are performed in the Density-Functional Theory framework, using gradient-corrected functionals, and a plane-wave basis set. Pre-resonance Raman intensities are estimated from Car-Parrinello molecular dynamics runs.

1.4 first-principles molecular dynamics

Abstract: Ab initio or first-principles methods have emerged in the last two decades as a powerful tool to probe the properties of matter at the microscopic scale. These approaches are used to derive macroscopic observables under the controlled condition of a “computational experiment,” and with a predictive power rooted in the quantum-mechanical description of interacting atoms and electrons. Density-functional theory (DFT) has become de facto the method of choice for most applications, due to its combination of reasonable scaling with system size and good accuracy in reproducing most ground state properties. Such an electronic-structure approach can then be combined with classical molecular dynamics to provide an accurate description of thermodynamic properties and phase stability, atomic dynamics, and chemical reactions, or as a tool to sample the features of a potential energy surface. In a molecular-dynamics (MD) simulation the microscopic trajectory of each individual atom in the system is determined by integration of Newton’s equations of motion. In classical MD, the system is considered composed of massive, point-like nuclei, with forces acting between them derived from empirical effective potentials. Ab initio MD maintains the same assumption of treating atomic nuclei as classical particles; however, the forces acting on them are considered quantum mechanical in nature, and are derived from an electronic-structure calculation. The approximation of treating quantummechanically only the electronic subsystem is usually perfectly appropriate, due to the large difference in mass between electrons and nuclei. Nevertheless, nuclear quantum effects can be sometimes relevant, especially for light