Paolo Giannozzi

Bio: Paolo Giannozzi is an academic researcher from University of Udine. The author has contributed to research in topics: Density functional theory & Ab initio. The author has an hindex of 38, co-authored 122 publications receiving 44408 citations. Previous affiliations of Paolo Giannozzi include Nest Labs & École Polytechnique Fédérale de Lausanne.

Core-level shift analysis of amorphous CdTeO x materials

Abstract: We show the importance of considering the detailed local distributions of oxygen atoms around tellu- rium in CdTeOx glasses when interpreting X-ray photo- emission experiments. We perform first principles calculations of core-level shifts that are used to compute X-ray photo-electron spectra. The core-level shifts are investigated by means of atomic density of states and a structural Voronoi analysis. We find that the dominating effect on the atomic core-level shift of tellurium is charge redistribution due to the oxygen atoms. There is however also a prominent effect from the geometrical arrangement of the oxygen neighbors.

Large-Scale Electronic Structure Calculations in Solids

Abstract: Electronic-structure calculations in solids have considerably evolved from early approaches (band structure calculations in periodic model potentials, aimed at reproducing simple crystals) into very sophisticated and powerful techniques. These techniques usually require no or very little experimental input beyond the basic information on atomic composition and some structural data. This is the origin of the (perhaps too ambitious) definitions of ab-initio, or first-principles, or (perhaps more appropriately) parameter-free, which usually label these techniques. In conjunction with the enormous increase in computer power (and the decrease in computer prices), ab-initio methods now allow us to accurately reproduce and even to predict electronic and structural properties of real materials, and not just the simplest ones. This predictive power makes a strong case in favour of ab-initio methods, whenever they are applicable, with respect to empirical or semiempirical methods. These are far less computationally demanding but also less reliable.

Structural and Electronic Properties of C60 and C60 Derivatives in the Solid Phases: Calculations Based on Density-Functional Theory

Abstract: Calculations based on density-functional theory have played (and continue to play) an important role in the characterization of fullerene-based materials. We discuss here several of these approaches applied to various metal fullenrides, and also present still unpublished results of our own calculations. In a number of cases we find that different calculations often result in different physical pictures for the same compound. Through specific comparison of the computational models and schemes, we provide the possibility to evaluate their validity. In addition, comparison with experiment clarifies to what extent major issues are still unresolved about the effects on doping in general and about the electronic behavior of fullendes and its relation with their structural properties in particular.

AB-Initio Molecular Dynamics Studies of Microclusters

Abstract: The study of the structural and electronic properties of microclusters is a field of growing interest. Ab-initio molecular dynamics has provided a new and important tool for the theoretical approach to these questions. Here we present some very recent results on small semiconductor aggregates with special reference to calculations of equilibrium shapes and temperature effects. Results of simulations on alkali-metal microclusters are briefly mentioned.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials

Abstract: QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.

First-principles simulation: ideas, illustrations and the CASTEP code

Abstract: First-principles simulation, meaning density-functional theory calculations with plane waves and pseudopotentials, has become a prized technique in condensed-matter theory. Here I look at the basics of the suject, give a brief review of the theory, examining the strengths and weaknesses of its implementation, and illustrating some of the ways simulators approach problems through a small case study. I also discuss why and how modern software design methods have been used in writing a completely new modular version of the CASTEP code.

Phonons and related crystal properties from density-functional perturbation theory

Abstract: This article reviews the current status of lattice-dynamical calculations in crystals, using density-functional perturbation theory, with emphasis on the plane-wave pseudopotential method. Several specialized topics are treated, including the implementation for metals, the calculation of the response to macroscopic electric fields and their relevance to long-wavelength vibrations in polar materials, the response to strain deformations, and higher-order responses. The success of this methodology is demonstrated with a number of applications existing in the literature.