Potential energy surface

About: Potential energy surface is a research topic. Over the lifetime, 11674 publications have been published within this topic receiving 307691 citations.

The H(3) (+) rovibrational spectrum revisited with a global electronic potential energy surface.

Abstract: In this paper, we have computed the rovibrational spectrum of the H(3) (+) molecule using a new global potential energy surface, invariant under all permutations of the nuclei, that includes the long range electrostatic interactions analytically. The energy levels are obtained by a variational calculation using hyperspherical coordinates. From the comparison with available experimental results for low lying levels, we conclude that our accuracy is of the order of 0.1 cm(-1) for states localized in the vicinity of equilateral triangular configurations of the nuclei, and changes to the order of 1 cm(-1) when the system is distorted away from equilateral configurations. Full rovibrational spectra up to the H(+)+H(2) dissociation energy limit have been computed. The statistical properties of this spectrum (nearest neighbor distribution and spectral rigidity) show the quantum signature of classical chaos and are consistent with random matrix theory. On the other hand, the correlation function, even when convoluted with a smoothing function, exhibits oscillations which are not described by random matrix theory. We discuss a possible similarity between these oscillations and the ones observed experimentally.

A study of the C(1D)+H2→CH+H reaction: Global potential energy surface and quantum dynamics

Abstract: The adiabatic global potential energy surface of the CH2 system for the first singlet state of A′ symmetry (a 1A′) has been computed. Ab initio, multireference, single and double configuration interaction calculations have been used to characterize this state. This potential energy surface has a calculated well depth of 99.7 kcal/mol relative to the C(1D)+H2 asymptote. The surface has no barrier for the perpendicular C2v geometry, but presents a large barrier (12.35 kcal/mol) for the collinear C∞v geometry. The ab initio calculations were carried out over 1748 geometries and the resulting energies were fitted to a many body expansion. Based on this surface, we have performed the first quantum reactive scattering calculations for the C(1D)+H2(X 1Σg+)→CH(X 2Π)+H(2S) reaction and total angular momentum J=0. The hyperspherical coordinates time-independent method has been used. We note that the state-to-state reaction probabilities as a function of the collision energy show a dense resonance structure which is unusual for this type of atom+diatom reaction. We present also rotational distributions.

Modeling Cytochrome Oxidase: A Quantum Chemical Study of the O−O Bond Cleavage Mechanism

Abstract: The mechanism of O−O bond cleavage at the binuclear center in cytochrome oxidase has been investigated by using hybrid density functional theory (B3LYP). A potential energy surface for the reaction step from compound A, with the O2 molecule coordinated to heme a3, to the bond-cleaved compound P is constructed. The features of the calculated potential surface agree well with experimental information on this reaction step. First, a free energy of activation of 15 kcal/mol is obtained, reasonably close to the value of 12 kcal/mol corresponding to the observed lifetime of compound A. Second, the calculations give a large entropy effect on the reaction rate, which explains the weak temperature dependence observed for the P formation reaction. Third, the calculated potential surface has no stable intermediate between A and P, in agreement with the experimental observation that compound A decays with the same rate as compound P forms. Fourth, the calculations show that the oxo−ferryl compound P together with a t...

On potential energy surfaces and relaxation to the global minimum

Abstract: By analyzing the dynamics of model potential energy surfaces we systematically investigate the processes involved in passing from a high energy state to the global minimum and how the probability of reaching the global minimum depends upon the topography and topology of the potential energy surface (PES). Relaxation to the global minimum is easiest for PES’s consisting of a single funnel (a set of convergent pathways which lead to the global minimum) with low barriers and a significant potential energy gradient towards the global minimum. The presence of additional funnels on the surface can severely reduce the rate of relaxation to the global minimum. Such secondary funnels act most efficiently as kinetic traps when they terminate at a low energy minimum, have a steep potential energy gradient and are wide (i.e., have a large configurational entropy) compared to the primary funnel. Indeed, it is even possible to construct PES’s for which the system relaxes to the minimum at the bottom of a secondary funnel rather than the global minimum and then remains in this metastable state over a long time scale. Our results for these model PES’s are discussed in the context of theoretical and experimental knowledge of the dynamics of proteins, clusters, and glasses.

The 1:1 glycine zwitterion‐water complex: An ab initio electronic structure study

Abstract: More than a dozen stationary points on the potential energy surface for the 1:1 glycine zwitterion—water complex have been investigated at Hartree-Fock or MP2 levels of theory with basis sets ranging from split valence (4-31G) to split valence plus polarization and diffuse function (6–31 + + G**) quality. Only one true minimum (GLYZWM, C1 symmetry) could be located on the potential energy surface. GLYZWM features a bridged water molecule acting as both a hydrogen bond acceptor and donor with the NH3− and CO2− units of the glycine zwitterion. The total hydrogen bond energy in GLYZWM is computed as 16 kcal/mol (MP2/6–31 ++ G** // 6–31 ++ G**, including corrections for basis set superpositions errors). The computed vibrational frequencies and normal mode forms of the GLYZWM complex resemble in many cases experimental assignments made for the glycine zwitterion in bulk water on the basis of Raman spectroscopy. © 1996 by John Wiley & Sons, Inc.