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(91) Production(s) de ISPAS S.
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Etude ab initio nanotubes de carbone fonctionnalisés
Auteur(s): Dennler S., Goze-Bac C., Hamad A.E., Ispas S.
(Affiches/Poster)
CINES 2006 (Montpellier, France, FR), 2006-09-19 |
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Ab initio investigation of functionalized carbon nanotubes : A case study for hydrogenation
Auteur(s): Dennler S., Goze-Bac C., Hamad A.E., Baaba R., Ispas S., Mauri F.
(Affiches/Poster)
GDR-E Science and applications of nanotubes (Obernai, FR), 2006-10-16 |
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First principles molecular dynamics simulations of a sodium tetrasilicate glass upon compression
Auteur(s): Ispas S., Benoit Magalie
(Affiches/Poster)
12th International Workshop on Computational physics and Materials Science Total Energy and force Methods (Trieste, Italy, FR), 2005-01-13 |
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Etude ab initio des mécanismes d'altération par l'eau des verres nucleaires
Auteur(s): Geneste G., Bouyer F., Ispas S., Kob W.
(Affiches/Poster)
GDR-DFT (Cap d'Agde, France, FR), 2005-05-18 |
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Développement de potentiels classiques pour la silice liquide
Auteur(s): Carre Antoine, Ispas S., Kob W.
(Affiches/Poster)
GDR - DFT (Cap d'Agde, France, FR), 2005-05-18 |
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Vibrational properties of a sodium tetrasilicate glass: Ab initio versus Classical Force Fields 
Auteur(s): Ispas S., Zotov N., De wispelaere S., Kob W.
Conférence invité: CONCIM International Conference on Non-Crystalline Inorganic Materials (Bonn, DE, 2003-04-08)
Actes de conférence: Journal of non-crystalline solids, vol. 351 p.1144-1150 (2005)
Texte intégral en Openaccess : 
Ref Arxiv: cond-mat/0306332
Ref. & Cit.: NASA ADS
Résumé: We have determined the vibrational properties of a sodium tetrasilicate(Na$_{2}$Si$_{4}$O$_{9}$) glass model generated by molecular dynamicssimulations. The study has been carried out using a classical valence forcefields approach as well as an {\it ab initio} approach in the framework of thedensity functional theory. The total and partial vibrational densities ofstates (VDOS) are presented, as well as some characteristics of the vibrationalmodes (participation ratios, correlation lengths). For the low-frequency bandsbelow 500 cm${}^{-1}$, we find that the shapes of the two calculated VDOS aswell as those of their corresponding partial VDOS are quite similar. For theintermediate- and high-frequency ranges, we observe larger discrepanciesbetween the two calculations. Using the eigenmodes of the dynamical matrix wealso calculate the polarized Raman spectra within the bond-polarizabilityapproximation. We find an overall agreement between the calculated parallelpolarized (VV) Raman spectra and the corresponding experimental spectrum.Regarding the perpendicular depolarized (VH) Raman spectrum, the comparison ofthe calculated spectra to the experimental data indicates a need for anadjustment of the VH bond-polarizability parameters.
Commentaires: 17 pages, 4 EPS figures, submitted to J. Non. Cryst.-Sol., corrected version following referee's comments
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First-principles calculation of O-17, Si-29, and Na-23 NMR spectra of sodium silicate crystals and glasses
Auteur(s): Charpentier T., Ispas S., Profeta M., Mauri F., Pickard C.J.
(Article) Publié:
The Journal Of Physical Chemistry B, vol. 108 p.4147-4161 (2004)
Résumé: This paper presents results of first-principles calculations of nuclear magnetic resonance (NMR) parameters: the chemical shielding tensor and the electric field gradient tensor, of some crystalline and amorphous sodium silicate systems. The calculations have been performed using the recently introduced gauge including projector augmented wave (GIPAW) method, which was especially devised for periodic systems. It provides an attractive alternative to the cluster approximation, used in the previous NMR theoretical studies of silicates systems. Moreover, within the GIPAW formalism, amorphous systems can be efficiently described via a supercell approach as demonstrated in this work. Five reference crystalline compounds of known structure (alpha-quartz, alpha-cristobalite SiO2, and the sodium silicates Na2SiO3, alpha-Na2Si2O5, and beta-Na2Si2O5) and two molecular dynamics models of the sodium tetrasilicate glass Na2Si4O9 (NS4) have been studied. The NS4 glass models were generated by a combination of classical and Car-Parrinello molecular dynamics simulations. The good agreement of the simulated Si-29 MAS NMR and O-17,Na-23 3Q-MAS NMR spectra with the corresponding experimental data demonstrates the accuracy of the GIPAW method. Using these numerically generated data, we have also been able to gain insight into the correlation between NMR parameters and local structural features.
Commentaires: English Article 807TT
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