Vers une nouvelle interprétation de la liaison chimique?

Abstract

AbstractsLe dicoupage de la densit6 Clectronique totale dans une moltcule, en contributions provenant des diverses orbitales, permet de dtfinir des regions orbitalaires de caracttre conventionnel dont la charge totale est Cgale B la somme des populations de Mulliken des orbitales constituant les diverses rtgions. La fluctuation relative de la charge de ces rtgions s'exprime simplement en fonction des populations de Mulliken et des indices de liaisons. Cette analyse de la densit6 dans des moltcules writes (saturtes ou conjugutes) permet de retrouver les liaisons chimiques de la graphie classique comme correspondant B des rtgions orbitalaires de charge voisine de 2 et prCsentant une fluctuation relative faible (10, 10). Compte tenu du caract@re dynamique que contient la notion de liaison, les rtsultats obtenus trouveraient une interprttation simple dans I'espace des phases. L'impuissance de la MCcanique quantique de donner une description dans cet espace expliquerait I'impossibilitC de dtduire de calculs quantiques la notion m&me de liaison chimique.In a molecule the partitioning of the total electronic density into contributions of the various orbitals allows us to define orbital regions having a conventional character and whose total charge is equal to the sum of Mulliken's populations of the orbitals constituting the various regions. The relative fluctuation of the charge in these regions is simply expressed in terms of the Mulliken populations and bond orders. I n various molecules (saturated or conjugated) this density analysis allows to find again the chemical bonds of the classical formulas as corresponding to orbital regions having a charge close to 2 and a weak (50.1 0) relative fluctuation, Given the dynamic character implied in the bond concept, our results should find a simple interpretation in phase space. The powerlessness of quantum mechanics to give a description in this space should explain the impossibility to deduce from quantum calculations the notion itself of chemical bond.Durch die Zerlegung der totalen Elektronendichte in einem Molekiil, in Orbitalbeitragen, werden Orbitalbereiche konventionnellen Charakters definiert, deren Gesamtladung gleich der Summe der entsprechenden Mulliken'schen Orbitalpopulationen ist. Die relative Fluktuation der Ladung dieser Bereiche wird als Funktion der Mulliken'schen Populationen und der Bindungsindizen ausgedriickt. Mit dieser Analyse der Dichte verschiedener Molekiile (gesattigte oder konjugierte) konnen die iiblichen chemischen Bindungen wiedergefunden werden, entsprechend Orbitalbereichen mit Ladung in der Nahe von 2 und mit einer ziemlich kleinen (50.10) Fluktuation. Wegen des dynamischen Charakters des Bindungsbegriffs wird vorgeschlagen, dass man fur die erhaltenen Ergebnisse eine einfache Interpretation im Phasenraum finden konnen soll. Die Unfahigkeit der Quantenmechanik eine Beschreibung dieses Raums zu geben wiirdc die Unmoglichkeit erklaren, den Begriff der chemischen Bindung aus Quantenrechnungen herzuleiten.

Theoretical study of the adsorption of silver atoms on the (111) face of silicon

“…These results show that the AgSi system is strongly localized. This conclusion is confirmed by the weak value of the relative fluctuation of the electron population of the orbital domain constituted by the dangling Si orbital and the s-Ag orbital [22] In the case of adsorption above site I, whatever value is used for This value corresponds to a single localized bond. In case 11, where the Ag atom is located above a Sig triangle, the lsi-Ag bond orders are necessarily weaker, and the bonds longer.…”

The Concept of Molecular Structure in Quantum Theory: Interpretation Problems

“…146 As may be guessed, the problem of the "classical limit" no longer exists in SED," since this theory is, in fact, genuinely classical. a and 7T) between the same two atoms.…”

“…a and 7T) between the same two atoms. 146 As may be guessed, the problem of the "classical limit" no longer exists in SED," since this theory is, in fact, genuinely classical. We simply have the limit in which the damping and fluctuating forces are negligible with respect to the "classical" or "deterministic" force F(r) and the inertial term mr, and consequently the "erratic part" of the motion becomes negligible with respect to the "classical" or "deterministic" part, associated with F(r) and mr only.…”

Electron pairing and chemical bonds: Pair localization in ELF domains from the analysis of domain averaged Fermi holes

“…Because of immense debt which chemistry owes to the classical model of molecule as composed of directionally oriented and well localized chemical bonds, it is not surprising that a lot of effort was and still is devoted to its reconciliation with the quantum mechanical description in terms of delocalized wave functions. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] One of the promising procedures which indeed seem to provide the desired link between the classical and quantum chemical description of chemical bonding is the approach based on the so-called electron localization function (ELF). [19][20][21][22] This function allows the unique partitioning of the molecule into disjunct domains, which indeed are reminiscent of classical chemical bonds.…”