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.

Graph Theory Meets Ab Initio Molecular Dynamics: Atomic Structures and Transformations at the Nanoscale

Abstract: Social permutation invariant coordinates are introduced describing the bond network around a given atom. They originate from the largest eigenvalue and the corresponding eigenvector of the contact matrix, are invariant under permutation of identical atoms, and bear a clear signature of an order-disorder transition. Once combined with ab initio metadynamics, these coordinates are shown to be a powerful tool for the discovery of low-energy isomers of molecules and nanoclusters as well as for a blind exploration of isomerization, association, and dissociation reactions.

Rotational excitation of ortho-H$_{2}$O by para-H$_{2}$ (j$_{2}$ = 0, 2, 4, 6, 8) at high temperature

Abstract: Aims. Our objective is to obtain the best possible set of rotational (de)-excitation state-to-state and effective rate coefficients for temperatures up to 1500 K. We present state-to-state rate coefficients among the 45 lowest levels of o-H2O with H2(j2 = 0) and Δj2 = 0, +2, as well as with H2(j2 = 2) and Δj2 = 0, −2. In addition and only for the 10 lowest energy levels of o-H2O, we provide state-to-state rate coefficients involving j2 = 4 with Δj2 = 0, − 2a ndj2 = 2 with Δj2 =+ 2. We give estimates of effective rate coefficients for j2 = 6, 8. Methods. Calculations are performed with the close coupling (CC) method over the whole energy range, using the same 5D potential energy surface (PES) as the one employed in our latest publication on water. We perform comparisons with coupled states (CS) calculations, with thermalized quasi-classical trajectory (QCT) calculations using the same PES and with previous quantum calculations obtained between T = 20 K and T = 140 K with a different PES. Results. We find that the CS approximation fares extremely badly even at high energy for j2 different from zero. Comparisons with thermalized QCT calculations show large factors at intermediate temperatures and factors from 1 to 3 at high temperature for the strongest rate coefficients. Finally we stress that scaled collisional rate coefficients obtained with He cannot be used in place of collisional rate coefficients with H2.

A new potential energy surface for the CH3+H2↔ CH4+H reaction: Calibration and calculations of rate constants and kinetic isotope effects by variational transition state theory and semiclassical tunneling calculations

Abstract: We present a sequence of three successively improved new semiempirical potential energy surfaces for the reaction CH3+H2→CH4+H. The semiempirical calibration is based on ab initio electronic structure calculations and experimental thermochemical data, vibrational frequencies, reaction rate constants, Arrhenius parameters, and kinetic isotope effects (KIE’s). To compare to the experimental kinetic data we apply variational transition state theory and semiclassical estimates of tunneling probabilities. We also provide detailed factorization analyses of the KIE’s to illustrate the way in which various surface features contribute to the overall KIE’s, and we discuss the substantial difficulties in attributing specific kinetic results to isolated potential energy surface features. Each of the three new surfaces, called J1, J2, and J3, has a thinner barrier than the one before. In addition, we provide one example, called surface J2A, showing the effect of making the barrier even thinner than on the best surface...

Quantum adsorption dynamics of a diatomic molecule on surface: Four‐dimensional fixed‐site model for H2 on Cu(111)

Abstract: We presented a detailed quantum dynamics study for dissociative adsorption of H2 at different sites of Cu(111) surface to investigate the effect of surface corrugation and site specificity. The theoretical study employed a four‐dimensional (4‐D) ‘‘fixed‐site’’ model, in which the lateral coordinates (X,Y) of the center of mass of the diatom are fixed at the impact site, but the remaining four degrees of freedom are explicitly treated in quantum calculations. The inclusion of the azimuthal angle φ in the present 4‐D model is a significant step forward in theoretical studies beyond the 3‐D ‘‘flat surface’’ model. This 4‐D ‘‘fixed‐site’’ model allows us to investigate explicitly the local corrugation effect that was not possible using the 3‐D flat‐surface model. We incorporated the latest ab initio data of Hammer et al. in constructing the LEPS potential energy surface, which gives the lowest dissociation barrier over the bridge site. 4‐D dynamics calculations are performed in the present study to mimic a no...

Structures of water octamers (H2O)8: exploration on ab initio potential energy surfaces by the scaled hypersphere search method.

Abstract: The potential energy surface (PES) of water octamers has been explored by the scaled hypersphere search method. Among 164 minima on the PES (based on MP2/6-311++G(3df,2p)//B3LYP/6-311+G(d,p) calculations), the cubic structure with D2d symmetry has been confirmed to be the global minimum. In a thermodynamic simulation using these 164 structures, the cubic structure with S4 symmetry has the highest population at low temperature, though double rings can become dominant as temperature going up, in good accord with a recent Monte Carlo simulation using an empirical potential. A transition temperature from cubic to noncubic has significantly been underestimated when potential energy data of B3LYP/6-311+G(d,p) calculations are employed in the simulation. This serious discrepancy between the MP2 and the B3LYP results suggests an importance of dispersion interactions for discussions on thermodynamics of water octamers.