Core repulsion effects in alkali trimers

The present paper is related to a talk presented during the Symposium on Coherent Control and Ultracold Chemistry held during the Sixth Congress of the International Society for Theoretical Chemical Physics (ISTCP-VI, July 2008). The talk was entitled "Electronic structure properties of alkali dimers and trimers. Prospects for alignment of ultracold molecules". Here we report on the electrostatic repulsion forces of the ionic cores at short separation, involved when the potential energy surfaces of alkali trimers are calculated with a quantum chemistry approach based on effective large-core potentials for ionic core description. We demonstrate that such forces in the triatomic molecule can be obtained as the sum of three pairwise terms. We illustrate our results on the lowest electronic states of Cs$_3$, which are computed for the first time within a full configuration interaction based on a large Gaussian basis set. As a preliminary section, we also propose a brief introduction about the importance of alkali trimer systems in the context of cold and ultracold molecules

Nucleation of a sodium droplet on C60

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 figure

Étude théorique de la régiosélectivité de l'ouverture des esters glycidiques par les organométalliques

Afin de contribuer à l'interprétation de la régiosélectivité de l'ouverture par les organométalliques des époxydes fonctionnalisés, nous avons étudié théoriquement la structure géométrique, la répartition des charges et la localisation des orbitales moléculaires du glycidate de méthyle non substitué ou substitué par un méthyle en C3 (configuration trans ou cis) et des complexes correspondants avec le cation lithium. Les calculs de type ab initio ont été effectués au niveau SCF avec une base minimale puis des bases étendues. Des trois facteurs possibles — électrostatique, stérique et de symétrie — seul le facteur stérique semble pouvoir expliquer la régiosélectivité de l'ouverture de ces composés par les cuprates lithiens