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108 results on '"Mijoule, C."'

1. Nucleation of a sodium droplet on C60

Author

Roques, J., Calvo, F., Spiegelman, F., and Mijoule, C.

Subjects
Condensed Matter - Materials Science
Abstract

We investigate theoretically the progressive coating of C60 by several sodium atoms. Density functional calculations using a nonlocal functional are performed for NaC60 and Na2C60 in various configurations. These data are used to construct an empirical atomistic model in order to treat larger sizes in a statistical and dynamical context. Fluctuating charges are incorporated to account for charge transfer between sodium and carbon atoms. By performing systematic global optimization in the size range 1<=n<=30, we find that Na_nC60 is homogeneously coated at small sizes, and that a growing droplet is formed above n=>8. The separate effects of single ionization and thermalization are also considered, as well as the changes due to a strong external electric field. The present results are discussed in the light of various experimental data., Comment: 17 pages, 10 figures

Published
2003
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2. Wetting to Non-wetting Transition in Sodium-Coated C_60

Author

Roques, J., Calvo, F., Spiegelman, F., and Mijoule, C.

Subjects
Physics - Atomic and Molecular Clusters, Physics - Chemical Physics
Abstract

Based on ab initi and density-functional theory calculations, an empirical potential is proposed to model the interaction between a fullerene molecule and many sodium atoms. This model predicts homogeneous coverage of C_60 below 8 Na atoms, and a progressive droplet formation above this size. The effects of ionization, temperature, and external electric field indicate that the various, and apparently contradictory, experimental results can indeed be put into agreement., Comment: 4 pages, 4 postscript figures

Published
2002
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12. Theoretical vibrational study of the FX···O(CH3)2 hydrogen-bonded complex.

Author

Bouteiller, Y., Mijoule, C., Szczesniak, M. M., and Scheiner, S.

Subjects
*HYDROGEN, *POTENTIAL energy surfaces, *VIBRATION (Mechanics)
Abstract

This paper presents the first ab initio attempt to reconstruct the observed band profile of the stretching fundamental vFX (X=H,D) in the FX···O(CH3)2 hydrogen-bonded system. The two-dimensional potential energy surface V(rFH,RF···O) is evaluated by means of large basis set SCF calculations. The related force constants up to the fourth order are obtained via the analytical fit to a polynomial expansion. The vibrational problem is solved by means of a variational treatment which includes the effects of mechanical anharmonicity. The side bands of the stretching fundamental vFX are described in terms of the vFX ±nvFX···O combination bands in excellent agreement with experiment. [ABSTRACT FROM AUTHOR]

Published
1988
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13. Quantum Monte Carlo method for some model and realistic coupled anharmonic oscillators.

Author

Caffarel, M., Claverie, P., Mijoule, C., Andzelm, J., and Salahub, D. R.

Subjects
QUANTUM theory, MONTE Carlo method, HARMONIC oscillators
Abstract

A new quantum Monte Carlo (QMC) method of evaluating low lying vibrational levels for coupled modes is presented. We use a modified fixed-node (FN) approach in which an extremum principle for energy levels is invoked. In this way, the nodal hypersurfaces of the nuclear wave function are parametrized and then optimized for each excited state. The method is tested on the fundamental excitations of some two-dimensional model potentials and is applied to the case of realistic coupled modes of the CO molecule adsorbed on a palladium cluster. The effect of an external electric field is also examined. The quantum Monte Carlo results are compared with those obtained in the conventional variational treatment of the nuclear Schrödinger equation for coupled vibrations. The QMC results give the exact values with an error which is in general less than 1 cm-1 . In all cases (even in the case of strong coupling) the use of our procedure leads to ‘‘optimal’’ nodal lines (in the sense of the extremum principle used in this work) which are practically undistorted. A salient feature of the Monte Carlo method presented here is that it readily permits the evaluation of the fundamental excitations of an arbitrary number of coupled vibrations. Furthermore, the potential energy surface may be represented by any analytical form without practical difficulties. [ABSTRACT FROM AUTHOR]

Published
1989
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37. Density Functional Study of Metal−Arene Compounds:  Mono(benzene)chromium, Bis(benzene)chromium and Their Cations

Author

Sahnoun, R. and Mijoule, C.

Abstract

To investigate the elementary events of the decomposition of transition metal complexes, a density functional study of the systems Cr(C6H6)2 and Cr(C6H6) as well as their corresponding cations, has been carried out. The results give a low bond energy (0.36 eV) for the neutral Cr(C6H6) compound while the binding energy of the cation Cr(C6H6)+ is much higher (1.84 eV), in good agreement with previous theoretical and experimental studies. Concerning the dissociation of Cr(C6H6)2, the first process (dissociation of the first ligand) needs much higher energy than the second one, and depends on the intersystem crossing relaxation (ISC) of the intermediate Cr(C6H6) compound. Taking into account the ISC process, the three-body decomposition occurs at 3.40 eV, in good agreement with recent experimental results. In the case of the Cr(C6H6)2+ dissociation, both processes (with and without ISC) may be available from recent experimental works. Our theoretical results reproduce very well the values corresponding to both ways of decomposition.

Published
2001

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