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.

Energy landscapes of model glasses. II. Results for constant pressure

Abstract: New geometry optimization techniques are introduced for characterizing local minima, transition states, and pathways corresponding to enthalpy surfaces at constant pressure. Results are obtained for comparison with the potential energy surfaces of model glass formers studied in previous work. The constant pressure condition, where the the box lengths of the simulation cell vary, makes the enthalpy surface less rugged than the potential energy surface corresponding to the same mean density. Analysis of barrier heights as a function of pressure provides insight into transport and relaxation processes. Elementary rearrangements can be separated into “diffusive” and “nondiffusive” processes, where the former involve changes in the nearest-neighbor coordination of at least one atom, and the latter do not. With increasing pressure the barrier heights for cage-breaking rearrangements rise, while those for cage-preserving rearrangements appear relatively unchanged. The “strong” or “fragile” character of the syste...

Fine and hyperfine excitation of C2H by collisions with He at low temperature

Abstract: Modelling of molecular emission from interstellar clouds requires the calculation of rate coefficients for excitation by collisions with the most abundant species. From a new, highly correlated, two-dimensional potential energy surface, rotational excitation of the C2H(X2Σ+) molecule by collision with He is investigated. State-to-state collisional excitation cross-sections between the 25 first fine structure levels of C2H are calculated for energies up to 800 cm−1 which yields after thermal averaging rate coefficients up to T= 100 K. The exact spin splitting of the energy levels is taken into account. The recoupling technique introduced by Alexander & Dagdigian allows us to deduce the corresponding temperature-dependent hyperfine state-to-state rate coefficients. Propensity rules are discussed.

Relaxed potential energy surfaces of N‐linked oligosaccharides: The mannose‐α(1 → 3)‐mannose case

Abstract: We report calculations of potential energy surfaces where all the internal coordinates of the disaccharide Man-α(1 → 3)-Man-α-O-Me were relaxed and minimized through an extensive molecular mechanics scheme. Flexibility within the mannopyranose rings plays a crucial role. Introduction of the relaxed principle into the conformational description of the disaccharide does not greatly alter the overall shape of the low-energy domains but it reveals new local minima. However, its principle effect is the lowering of energy barriers in the potential energy surface. New conformational transitions about the glycosidic bonds appear, permiting pathways among the low energy sections. This occurs with only little variation of the classical 4C1 conformation of the mannopyranose residues. All the conformations observed in the solid state, along with those already predicted through the joint use of NMR and modeling techniques, fall into the populations of stable conformers calculated in the present work. Moreover, a satisfactory agreement is reached between previously observed NOE values, and the theoretical one, calculated from the averaging of more than 500 microstates. The present results reconciliate most of the apparently conflicting data previously reported; they provide strong support for the application of the concept of conformational averaging to solution behavior. Some limitations of the proposed methodology are also discussed.

Coupled translation-rotation eigenstates of H2 in C60 and C70 on the spectroscopically optimized interaction potential: Effects of cage anisotropy on the energy level structure and assignments

Abstract: We have developed a quantitatively accurate pairwise additive five-dimensional (5D) potential energy surface (PES) for H2 in C60 through fitting to the recently published infrared (IR) spectroscopic measurements of this system for H2 in the vibrationally excited ν=1 state. The PES is based on the three-site H2–C pair potential introduced in this work, which in addition to the usual Lennard-Jones (LJ) interaction sites on each H atom of H2 has the third LJ interaction site located at the midpoint of the H–H bond. For the optimal values of the three adjustable parameters of the potential model, the fully coupled quantum 5D calculations on this additive PES reproduce the six translation-rotation (T-R) energy levels observed so far in the IR spectra of H2@C60 to within 0.6%. This is due in large part to the greatly improved description of the angular anisotropy of the H2-fullerene interaction afforded by the three-site H2–C pair potential. The same H2–C pair potential spectroscopically optimized for H2@C60 wa...

Analytic function for the H + CH/sub 3/ in equilibrium CH/sub 4/ potential energy surface

Abstract: An analytic function for the ground electronic state CH/sub 4/ in equilibrium CH/sub 3/ + H potential energy surface is proposed. This model makes use of a switching-function formalism and is based on both spectroscopic data and ab initio calculations at the MP4/6-31G** level. The proposed general symmetric analytic potential is suitable for use in quasiclassical trajectory studies of the CH/sub 4/ in equilibrium CH/sub 3/ + H reaction. 9 figures, 4 tables.