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.

Conformational analysis and molecular dynamics simulations of maltose.

Abstract: Constrained conformational energy minimizations have been used to calculate an adiabatic (Φ, ψ) potential energy surface for the disaccharide β-maltose. The inclusion of molecular flexibility in the conformational energy analysis of the disaccharide was found to significantly lower the barriers to conformational transitions, as has been observed previously for other systems. Several low energy wells were identified on the adiabatic surface which differ in energy by small amounts and with low absolute barriers separating them, indicating the possibility of a non-negligible equilibrium population distribution in each well. If such a distribution of conformations existed in the physical system, the conformation observed by NMR NOE measurements would thus be a “virtual” conformation. Molecular dynamics simulations of the motions of this molecule in vacuum were also conducted and indicate that the rate of relaxation of the molecule to the adiabatic surface may be slower than the typical timescale of conformational fluctuations. This effect is apparently due to an unphysical persistence of hydrogen bond patterns in vacuum which does not occur in aqueous solution. Trajectories undergoing transitions between wells were calculated and the effects of such conformational transitions upon the ensemble mean structure, such as might be observed in an NMR experiment, were demonstrated.

Zero-point vibrational effects on proton shieldings: functional-group contributions from ab initio calculations.

Abstract: We investigate the effects of zero-point vibrational motion on the nuclear magnetic shielding constants of a large number of organic molecules. The vibrational corrections include anharmonic contributions from the potential energy surface and harmonic contributions from the curvature of the property surface. Particular attention is paid to vibrational corrections to hydrogen shielding constants where we show that vibrational corrections may be substantial, ranging from about +0.50 to −0.70 ppm, and thus demonstrating that ignoring these effects may give errors in the chemical shifts by more than 1 ppm in certain extreme cases. These effects can therefore not be neglected when comparing calculated results with experiment, not even for the chemical shifts. However, we also demonstrate that the vibrational corrections to the hydrogen shieldings are to a large extent transferable from one molecule to another. We have tabulated functional vibrational corrections to the hydrogen shieldings, based on results for...

Femtosecond Dynamics of a Hydrogen-Bonded Model Base Pair in the Condensed Phase: Double Proton Transfer in 7-Azaindole

Abstract: Femtosecond, real-time dynamics of a hydrogen-bonded model base pair (7-azaindole dimer) in the condensed phase is presented and compared with gas-phase, molecular beam studies. Following the preparation of a wave packet (nonequilibrium state), we resolved the initial decay of the reactive pair and the rise of the tautomer in two solvents. Studies of the isotope effect, solvent viscosity, energy dependence, and polarization anisotropy are consistent with direct and indirect reaction pathways for the double proton transfer on a global potential energy surface.

Metastable states of ozone calculated on an accurate potential energy surface

Abstract: A new potential energy surface for ozone is developed. It is based on high level ab initio data and includes an accurate description of the barrier region. Full quantum reactive scattering calculations using a coupled channel approach and hyperspherical coordinates are performed on this surface for various isotopic compositions of ozone. Collision lifetimes are obtained over a wide energy range, which gives the spectrum of rovibrational metastable states (scattering resonances). This spectrum is discovered to be very nonstatistical. The spectrum of resonances is dense below the isotopic zero-point-energy threshold and sparse above it. This feature is explained by the opening of additional dissociation channels at higher energies. This behavior is a general quantum mechanical effect that should occur in other triatomic molecules.

Classical trajectories using the full abinitio potential energy surface H−+CH4→CH4+H−

Abstract: The classical trajectory method has been coupled with the gradient evaluation of the ab initio potential energy with respect to nuclear coordinates to study molecular dynamics. Trajectories, starting from a known transition state, can be computed in the full space of Cartesian coordinates in order to provide information on the reaction dynamics. The nucleophilic substitution reaction H−+CH4→CH4+H− is treated as an example and is shown to occur via a nonadiabatic path where initial vibrational energy of the methane molecule is essential for reaction.