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Francesco Mauri

Bio: Francesco Mauri is an academic researcher from Sapienza University of Rome. The author has contributed to research in topics: Graphene & Phonon. The author has an hindex of 85, co-authored 352 publications receiving 69332 citations. Previous affiliations of Francesco Mauri include University of Texas at Arlington & University of California, Berkeley.


Papers
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TL;DR: In this article, the theoretical infrared and Raman spectra of the gibbsite [α-Al(OH) 3 ] were computed using ab initio quantum mechanical calculations and the low-frequency dielectric tensor and the Raman tensors of the Gibbsite were determined using linear response theory.
Abstract: The theoretical infrared (IR) and Raman spectra of gibbsite [α-Al(OH) 3 ] were computed using ab initio quantum mechanical calculations. The low-frequency dielectric tensor and the Raman tensors of gibbsite were determined using linear response theory. The transmission powder IR spectrum was found to strongly depend on the shape of the gibbsite particles. In the region of the OH-stretching bands, an excellent agreement between theory and experiment was obtained, providing an unambiguous interpretation of the OH bands in terms of vibrational modes. In contrast, the assignment of the bands observed at lower frequency is complicated by the significant overlap between neighboring bands together with their sensitivity to particle shape.

125 citations

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TL;DR: In this article, the role of electronic screening on the electron-phonon matrix elements is carefully investigated, and the contribution of acoustic phonons to resistivity is doping and substrate independent, in agreement with experimental observations.
Abstract: We use first-principles calculations, at the density-functional-theory (DFT) and GW levels, to study both the electron-phonon interaction for acoustic phonons and the "synthetic" vector potential induced by a strain deformation (responsible for an effective magnetic field in case of a nonuniform strain). In particular, the interactions between electrons and acoustic phonon modes, the so-called gauge-field and deformation potential, are calculated at the DFT level in the framework of linear response. The zero-momentum limit of acoustic phonons is interpreted as a strain of the crystal unit cell, allowing the calculation of the acoustic gauge-field parameter (synthetic vector potential) within the GW approximation as well. We find that using an accurate model for the polarizations of the acoustic phonon modes is crucial to obtain correct numerical results. Similarly, in the presence of a strain deformation, the relaxation of atomic internal coordinates cannot be neglected. The role of electronic screening on the electron-phonon matrix elements is carefully investigated. We then solve the Boltzmann equation semianalytically in graphene, including both acoustic and optical phonon scattering. We show that, in the Bloch-Gruneisen and equipartition regimes, the electronic transport is mainly ruled by the unscreened acoustic gauge field, while the contribution due to the deformation potential is negligible and strongly screened. We show that the contribution of acoustic phonons to resistivity is doping and substrate independent, in agreement with experimental observations. The first-principles calculations, even at the GW level, underestimate this contribution to resistivity by approximate to 30%. At high temperature (T > 270 K), the calculated resistivity underestimates the experimental one more severely, the underestimation being larger at lower doping. We show that, besides remote phonon scattering, a possible explanation for this disagreement is the electron-electron interaction that strongly renormalizes the coupling to intrinsic optical-phonon modes. Finally, after discussing the validity of the Matthiessen rule in graphene, we derive simplified forms of the Boltzmann equation in the presence of impurities and in a restricted range of temperatures. These simplified analytical solutions allow us the extract the coupling to acoustic phonons, related to the strain-induced synthetic vector potential, directly from experimental data.

120 citations

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TL;DR: In this article, the authors derived the exact analytic formula for the second derivative of the free energy in the self-consistent harmonic approximation for a generic atomic configuration, expressed in terms of the atomic displacements and forces in a form that can be evaluated by a stochastic technique.
Abstract: The self-consistent harmonic approximation is an effective harmonic theory to calculate the free energy of systems with strongly anharmonic atomic vibrations, and its stochastic implementation has proved to be an efficient method to study, from first-principles, the anharmonic properties of solids. The free energy as a function of average atomic positions (centroids) can be used to study quantum or thermal lattice instability. In particular the centroids are order parameters in second-order structural phase transitions such as, e.g., charge-density-waves or ferroelectric instabilities. According to Landau's theory, the knowledge of the second derivative of the free energy (i.e., the curvature) with respect to the centroids in a high-symmetry configuration allows the identification of the phase-transition and of the instability modes. In this work we derive the exact analytic formula for the second derivative of the free energy in the self-consistent harmonic approximation for a generic atomic configuration. The analytic derivative is expressed in terms of the atomic displacements and forces in a form that can be evaluated by a stochastic technique using importance sampling. Our approach is particularly suitable for applications based on first-principles density-functional-theory calculations, where the forces on atoms can be obtained with a negligible computational effort compared to total energy determination. Finally, we propose a dynamical extension of the theory to calculate spectral properties of strongly anharmonic phonons, as probed by inelastic scattering processes. We illustrate our method with a numerical application on a toy model that mimics the ferroelectric transition in rock-salt crystals such as SnTe or GeTe.

119 citations

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TL;DR: Dense functional theory is used to compute the effect of both electron-phonon coupling and anharmonicity on the linewidth of MgB2, obtaining excellent agreement with experiment.
Abstract: We measure phonon dispersion and linewidth in a single crystal of MgB2 along the Gamma-A, Gamma-M, and A-L directions using inelastic x-ray scattering. We use density functional theory to compute the effect of both electron-phonon coupling and anharmonicity on the linewidth, obtaining excellent agreement with experiment. Anomalous broadening of the E(2g) phonon mode is found all along Gamma-A. The dominant contribution to the linewidth is always the electron-phonon coupling.

118 citations

Journal ArticleDOI
TL;DR: In this paper, a joint theoretical and experimental study is presented to characterize the dissociation products of compressed H${}_{2}$S, which is essential to understand its complex superconducting states.
Abstract: Hydrogen sulfides have recently received a great deal of interest due to the record high-${T}_{c}$ of up to 203 K observed on strong compression of H${}_{2}$S . In this paper, a joint theoretical and experimental study is presented to characterize the dissociation products of compressed H${}_{2}$S , which is essential to understand its complex superconducting states. Based on the results here, the authors found H${}_{2}$S partially decomposes into S + H${}_{3}$S + H${}_{4}$S${}_{3}$ above 27 GPa, and H${}_{4}$S${}_{3}$ emerges as the major component at around 66 GPa. Interestingly, x-ray diffraction (XRD) experiments observed a small fraction of H${}_{3}$S and residual H${}_{2}$S at least up to 140 GPa, which are believed to be responsible for the two superconducting states observed in experiments. This paper provides the first XRD evidence on the existence of H${}_{3}$S at high pressure from the decomposition of H${}_{2}$S.

118 citations


Cited by
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Journal ArticleDOI
TL;DR: A detailed description and comparison of algorithms for performing ab-initio quantum-mechanical calculations using pseudopotentials and a plane-wave basis set is presented in this article. But this is not a comparison of our algorithm with the one presented in this paper.

47,666 citations

Journal ArticleDOI
TL;DR: Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena can now be mimicked and tested in table-top experiments.
Abstract: Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.

35,293 citations

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08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

01 May 1993
TL;DR: 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.
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.

29,323 citations

Journal ArticleDOI
TL;DR: In this paper, the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations, are discussed.
Abstract: This article reviews the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic fields, or by altering sample geometry and/or topology. The Dirac electrons behave in unusual ways in tunneling, confinement, and the integer quantum Hall effect. The electronic properties of graphene stacks are discussed and vary with stacking order and number of layers. Edge (surface) states in graphene depend on the edge termination (zigzag or armchair) and affect the physical properties of nanoribbons. Different types of disorder modify the Dirac equation leading to unusual spectroscopic and transport properties. The effects of electron-electron and electron-phonon interactions in single layer and multilayer graphene are also presented.

20,824 citations