Détermination, représentation et interprétation des surfaces de potentiel

Cette brève revue examine quelques problèmes liés à la notion de surface de potentiel. Le domaine concerné est très vaste puisqu'il s'agit autant de la qualité des calculs ab- initio utilisés pour la détermination de la valeur de l'énergie en certains points singuliers, des techniques de représentation par des fonctions analytiques simples d'une surface déjà caractérisée, que des méthodes qui se proposent d'éviter cette étape de représentation intermédiaire. Chaque point particulier est illustré par un ou plusieurs exemples tirés de la littérature récente

Effective group potentials. 1. Method

in the first paper of this series, we will describe a method, called effective group potentials (EGP), aimed at simplifying molecular ab initio calculations for large systems involving bulky ligands as long as these ligands can he supposed to play the role of spectator groups. This method should be applicable to all types of bondings between active and the spectator parts. The different steps used in the definition of the ECP are closely related to those used for atomic effective core potentials (ECP) which are commonly used with great success in ab initio calculations involving heavy atoms

New effective potentials extraction method for the interaction between cations and water

A very simple method for the extraction of effective interaction potentials from ab initio calculations was proposed (Periole et al. J. Phys. Chem. 1997, 101, 5018), and simple two-body cation-water interaction potentials were derived for several cations, Li+, Na+, K+, Be2+, Mg2+, and Ca2+, using two facts: first, water molecules in the close vicinity of cations are strongly structured and present a constrained orientation towards the io

Can extrapolation to the basis set limit be an alternative to the counterpoise correction? A study on the helium dimer

Abstract Configuration interaction and coupled cluster calculations are reported for He2 using various orbital basis sets of the d-aug-AVXZ type, with the results being extrapolated to the one electron basis set limit both with counterpoise and without counterpoise correction. A generalized uniform singlet- and triplet-pair extrapolation scheme has been utilized for such a purpose. Using appropriate corrections to mimic full configuration interaction, the energies were predicted in excellent agreement with the best available estimates. The results also suggest that extrapolation to the complete basis set limit may be a general alternative to the counterpoise correction that yields a more accurate potential energy while being more economical