Molecular potential energy surfaces

The result is that, to a very good approxunation, as treated elsewhere in this Encyclopedia, the nuclei move in a mechanical potential created by the much more rapid motion of the electrons. The electron cloud itself is described by the quantum mechanical theory of electronic structure. Since the electronic and nuclear motion are approximately separable, the electron cloud can be described mathematically by the quantum mechanical theory of electronic structure, in a framework where the nuclei are fixed. The resulting Bom-Oppenlieimer potential energy surface (PES) created by the electrons is the mechanical potential in which the nuclei move. Wlien we speak of the internal motion of molecules, we therefore mean essentially the motion of the nuclei, which contain most of the mass, on the molecular potential energy surface, with the electron cloud rapidly adjusting to the relatively slow nuclear motion. 

HypcrC. hcm provides calculations IhaL explore molecular potential energy surfaces. Indeed, most of computational chemistry relates in one way or another to molecular potential energy surfaces, the topography of the surface and motion on the surface. 

Cee M L and M Page 1993. Computing Reaction Pathways on Molecular Potential Energy Surfaces. In Lipkowitz K B and D B Boyd (Editors). Reviews in Computational Chemistry Volume 4. New York, VCH Publishers, pp. 35-65. 

E. Kracka, T. H. Dunning, Jr., Advances in Molecular Electronic Structure Theory Calculation and Characterization of Molecular Potential Energy Surfaces T. H. Dunning, Jr. Ed., 129, JAI, Greenwich (1990). 

CM Becker. Principal coordinate maps of molecular potential energy surfaces. J Comput Chem 19 1255-1267, 1998. 

During the last decades, a large body of structural information has been derived from gas-electron diffraction studies. The corresponding results are nearly exclusively reported in the literature in terms of r distances, or the equivalent thermal average intemuclear distances, which are denoted r. The r distances are defined by the relation, r = r — If. Alternative methods for interpreting gas-electron diffraction data are possible, for example, in terms of -geometries5, but they are currently too complex to apply in routine stmctural analyses, because they require detailed information on the molecular potential energy surface which is not usually available. 

Michael L. McKee and Michael Page, Computing Reaction Pathways on Molecular Potential Energy Surfaces. 

The molecular potential energy surface is one of the most important concepts of physical chemistry. It is at the foundations of spectroscopy, of chemical kinetics and of the study of the bulk properties of matter. It is a concept on which both qualitative and quantitative interpretations of molecular properties can be based. So firmly is it placed in the theoretical interpretation of chemistry that there is a tendency to raise it above the level of a concept by ascribing it some physical reality. 

How sensitive is the computed control field to fluctuations in the field source and to uncertainties in the molecular potential-energy surface ... 

The optimization of minima and saddle points of a function in many variables is reviewed. Emphasis is on methods applicable to the calculation of electronic wave functions (ground and excited states) and the optimization of minima and transition states of molecular potential energy surfaces. 

Raman Studies of Molecular Potential Energy Surface Changes in Supercritical Fluids... 

BEN-AMOTZ ET AL. Molecular Potential Energy Surface Changes... 

McKee ML, Page M. Computing reaction pathways on molecular potential energy surfaces. In Lipkowitz KB, Boyd DB, eds. Reviews in Computational Chemistry. Vol. 4. New York VCH, 1993 35-65. 

Ewing, G.E. (1981). Vibrational predissociation of van der Waals molecules and inter-molecular potential energy surfaces, in Potential Energy Surfaces and Dynamics Calculations, ed. D.G. Truhlar (Plenum Press, New York). 

By taking as a reference the calculation in vacuo, the presence of the solvent introduces several complications. In fact, besides the direct effect of the solvent on the solute electronic distribution (which implies changes in the solute properties, i.e. dipole moment, polarizability and higher order responses), it should be taken into account that indirect solvent effects exist, i.e. the solvent reaction field perturbs the molecular potential energy surface (PES). This implies that the molecular geometry of the solute (the PES minima) and vibrational frequencies (the PES curvature around minima in the harmonic approximation) are affected by the presence of a solvating environment. Also, the dynamics of the solvent molecules around the solute (the so-called nonequilibrium effect ) has to be... 

III CROSSING OR PSEUDOCROSSING OF MOLECULAR POTENTIAL-ENERGY SURFACES... 

---