The Concept of Molecular Structure

Abstract

After a brief discussion of the classical origins of the idea of molecular structure it is shown what steps are necessary to exhibit molecular structure in solutions of the Schrodinger equation for a system that might intuitively be believed to be an isolated molecule. It is demonstrated that there is no straightforward or independent way in which molecular structure, as exemplified by a definite molecular geometry and associated properties, can be derived from such solutions. It is argued that the idea of a molecular structure does not fit easily into any feasible computational scheme for obtaining accurate solutions and it is suggested that as calculations develop in complexity and sophistication it is likely that quantum chemists will abandon the idea of molecular structure even as a starting point. An attempt is made to pur these observations in the broader context of the current debate initiated by such workers as Woolley and Claverie.

Nonadiabatic Calculation of Dipole Moments

“…Other general expressions for the translation-free internal coordinates have already been discussed by Sutcliffe and Woolley [7][8][9][10]. It is a most important topic in the nonadiabatic quantum mechanical approach to atoms and molecules.…”

“…This result is an obvious consequence of the average over the angular degrees of freedom of the whole system. The proper use of the body-fixed set of axes was clearly addressed by Blinder [39,40] in his studies on the HD molecule, and Sutcliffe [7][8][9]51] discussed the more general case of polyatomic molecules. For simplicity, here we restrict ourselves to Blinders proposal for diatomic molecules [39,40].…”