Showing papers by "Francesco Mauri published in 2001"
TL;DR: A theory for the ab initio calculation of all-electron NMR chemical shifts in insulators using pseudopotentials is presented in this article, which is formulated for both finite and infinitely periodic systems and is based on an extension to the projector augmented-wave approach of Bl\"ochl [P. E. Blachl, Phys. Rev. B 50, 17 953 (1994)] and the method of Mauri et al.
Abstract: A theory for the ab initio calculation of all-electron NMR chemical shifts in insulators using pseudopotentials is presented. It is formulated for both finite and infinitely periodic systems and is based on an extension to the projector augmented-wave approach of Bl\"ochl [P. E. Bl\"ochl, Phys. Rev. B 50, 17 953 (1994)] and the method of Mauri et al. [F. Mauri, B. G. Pfrommer, and S. G. Louie, Phys. Rev. Lett. 77, 5300 (1996)]. The theory is successfully validated for molecules by comparison with a selection of quantum chemical results, and in periodic systems by comparison with plane-wave all-electron results for diamond.
1,516 citations
TL;DR: In this paper, the theoretical infrared spectrum of kaolinite [Al2Si2O5(OH)4, triclinic] was computed using ab initio quantum mechanical calculations.
Abstract: The theoretical infrared spectrum of kaolinite [Al2Si2O5(OH)4, triclinic] was computed using ab initio quantum mechanical calculations. Calculations were performed using the Density Functional Theory and the generalized gradient approximation. The low-frequency dielectric tensor of kaolinite was determined as a function of the light frequency using linear response theory. The IR spectrum was then calculated using a model that takes into account the shape and size of kaolinite particles. A remarkable agreement was obtained between theory and experiment, especially on the position of the stretching bands of OH groups. This agreement provides a firm basis for the interpretation of the IR spectrum of kaolinite in terms of structural parameters.
212 citations
TL;DR: Density functional theory is demonstrated to reproduce the 13C and 11B NMR chemical shifts of icosahedral boron carbides with sufficient accuracy to extract previously unresolved structural information from experimental NMR spectra.
Abstract: Density functional theory is demonstrated to reproduce the C-13 and B-11 NMR chemical shifts of icosahedral boron carbides with sufficient accuracy to extract previously unresolved structural information from experimental NMR spectra. B4C can be viewed as an arrangement of 3-atom linear chains and 12-atom icosahedra. According to our results, all the chains have a CBC structure. Most of the icosahedra have a B11C structure with the C atom placed in a polar site, and a few percent have a B-12 structure or a B10C2 structure with the two C atoms placed in two antipodal polar sites.
154 citations
TL;DR: In this article, the vibrational eigenmodes and eigenvalues using density functional theory in the local density approximation, and the Raman intensities using a tight binding approximation were determined for tetrahedrous amorphous carbon.
Abstract: We present a practical method to compute the vibrational resonant Raman spectra in solids with delocalized excitations. We apply this approach to the study of tetrahedrous amorphous carbon. We determine the vibrational eigenmodes and eigenvalues using density functional theory in the local density approximation, and the Raman intensities using a tight binding approximation. The computed spectra are in good agreement with the experimental ones measured with visible and UV lasers. We analyze the Raman spectra in terms of vibrational modes of microscopic units. We show that, at any frequency, the spectra are dominated by the stretching vibrations. We identify a very rapid inversion in the relative Raman intensities of the $sp^2$ and $sp^3$ carbon sites with the frequency of the incident laser beam. In particular, the spectra are dominated by $sp^2$ atoms below 4 eV and by $sp^3$ atoms above 6 eV.
32 citations
TL;DR: In this article, the interaction of aqueous species with the (100) face of zircon using first-principles quantum mechanical calculations was studied, and it was shown that the strong acidity of the Zr-O-Si bridging O atoms promotes the associative adsorption of water on the surface of Zircon.
Abstract: We have studied the interaction of aqueous species with the (100) face of zircon using first-principles quantum mechanical calculations. Adsorption energy of molecular water on the Zr Lewis site is 1.27 eV per molecule, whereas the energy of dissociative adsorption is only 0.84 eV per molecule. Thus, the non-dissociative adsorption of water is strongly preferred with respect to the dissociative adsorption on the (100) face of zircon. Such behavior, which is related to the weak ability of the surface structure to relax, is changed by a 5% increase of the surface cell parameters. From our theoretical results, we propose that the exceptional resistance of zircon to dissolution may be related to the strong acidity of the Zr-O-Si bridging O atoms, which promotes the associative adsorption of water on the (100) surface of zircon.
12 citations
TL;DR: In this article, the distortion of the chromium site has been independently calculated through ab initio molecular dynamics, and the analysis of the isotropic and dichroic Extended X-ray Absorption Fine Structures at the Cr K-edge has been measured in the distorted chromium coordination shell.
Abstract: The crystallographic distortion around chromium and iron has been investigated by use of both theoretical and experimental methods. Through the analysis of the isotropic and dichroic Extended X-ray Absorption Fine Structures at the Cr K-edge, the Cr–O distances have been measured in the distorted chromium coordination shell. Through ab initio molecular dynamics, the distortion of the chromium site has been independently calculated.
3 citations
TL;DR: In this article, a recent development in the theory of quasicrystal-related four-coordinated structures is presented, and two crystalline approximants, 1/0 (known as the BC8 phase) and 1/1, are studied in detail.
Abstract: After an introductory survey, a recent development in the theory of quasicrystal-related four-coordinated structures is presented. Two crystalline approximants, 1/0 (known as the BC8 phase) and 1/1, are studied in detail. A novel method for construction of four-coordinated structures from the Frank-Kasper dense-packed systems is suggested and several new structures are constructed. The energies of those structures and topological phason disorder are studied ab initio.
2 citations