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.

DFT study of graphene doping due to metal contacts

Abstract: The experimental results of Metal-graphene (M-G) contact resistance R C have been investigated in-depth by means of Density Functional Theory (DFT). The simulations allowed us to build a consistent picture explaining the R C dependence on the metal contact materials employed in this work and on the applied back-gate voltage. In this respect, the M-G distance is paramount in determining the R C behavior.

First-principles calculations of hydrogen in bulk GaAs

Abstract: We present the results of first-principles calculations of the properties of neutral (H0) and charged (H+ and H-) hydrogen in bulk GaAs. The equilibrium sites are determined, and the electronic properties for the equilibrium positions are studied. H+ behaves as a deep donor and prefers to stay in a high valence charge region which includes the bond center. H- behaves as a deep acceptor and prefers the low valence charge region near a tetrahedral site. H0 has an amphoteric behaviour depending on the site it occupies. We compare our results with the results of calculations for H in Si.

Phonon Spectra of Ultrathin GaAs/AlAs Superlattices

Abstract: This paper presents some recent results of ab initio calculations of the dynamical properties of GaAs/AlAs superlattices (SL’s) grown along the (001) direction. In particular we will focus on open problems in the interpretation of the experimental thickness-dependence of the zone center longitudinal optical (LO) SL frequencies in the ultrathin (UT) regime, and clarify the origin of the major discrepancy between the measured Raman spectra and the previous theoretical predictions. This will allow us to draw conclusions on structural properties of such systems, and obtain indications on how LO modes can give useful information for characterization also in UT structures.

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.