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.

Search for Low Energy Structures of Water Clusters (H2O)n, n = 20−22, 48, 123, and 293

Abstract: A search for low energy structures of water clusters was performed with a combination of three computational tools: (a) temperature-dependent classical trajectories; (b) hydrogen network improvement; (c) rigid body diffusion Monte Carlo calculation on a smoothed potential energy surface. For the sizes of our main interest, n = 48, 123, and 293, input configurations included spheroid structures cut from crystalline ice, and amorphous structures. For n = 48, tube and sandwich minima were explored as well. The lowest energy configurations found were characterized by compact three-dimensional shapes. In the case of n = 48 and 123, crystallinity was lost in the course of the optimization; for these sizes, one finds four-, five-, and six-membered rings of water molecules, On the other hand, the lowest energy structure found for n = 293 includes a crystal core, dominated by six-membered rings, and an amorphous surface.

On the properties of X⋅⋅⋅N noncovalent interactions for first-, second-, and third-row X atoms

Abstract: In addition to a structure with a PH⋅⋅⋅N H-bond, a second complex of greater stability is formed when the PH3 is rotated such that its P-H bond is pointing away from the approaching N lone pair of NH3. Quantum calculations are applied to examine whether such a complex is characteristic only of P, or may occur as well for other atoms of the first, second, or third rows of the periodic table. The molecules PH3, H2S, HCl, AsH3, and NH3 are all paired with NH3 as electron donor. While NH3 will not engage in an N⋅⋅⋅N attraction, all the others do form a X⋅⋅⋅N complex. The energetics, geometries, and other properties of these complexes are relatively insensitive to the nature of the X atom. This uniformity contrasts sharply with the H-bonded XH⋅⋅⋅N complexes where a strong sensitivity to X is observed. The three-dimensional nature of the electrostatic potential, in conjunction with the striving for a linear H-X⋅⋅⋅N orientation that maximizes charge transfer, serves as an excellent tool in understanding both the shape of the potential energy surface and the proclivity to engage in a X⋅⋅⋅N interaction.

Reaction dynamics of methane with F, O, Cl, and Br on ab initio potential energy surfaces.

Abstract: The bimolecular hydrogen abstraction reactions of methane with atoms have become benchmark systems to test and extend our knowledge of polyatomic chemical reactivity. We review the state-of-the-art methodologies for reaction dynamics computations of X + methane [X = F, O(3P), Cl, Br] reactions, which consist of two key steps: (1) potential energy surface (PES) developments and (2) reaction dynamics computations on the PES using either classical or quantum methods. We briefly describe the permutationally invariant polynomial approach for step 1 and the quasiclassical trajectory method, focusing on the mode-specific polyatomic product analysis and the Gaussian binning (1GB) techniques, and reduced-dimensional quantum models for step 2. High-quality full-dimensional ab initio PESs and dynamical studies of the X + CH4 and CHD3 reactions are reviewed. The computed integral cross-sections, angular, vibrational, and rotational product distributions are compared with available experiments. Both experimental and t...

Polarizable Continuum Reaction-Field Solvation Models Affording Smooth Potential Energy Surfaces

Abstract: Apparent surface charge, reaction-field solvation models often employ overlapping atomic spheres to represent the solute/continuum boundary. Discretization of the solute cavity surface, however, results in a boundary-element method that fails to afford a continuous potential energy surface for the solute. Several proposed remedies for this problem, based upon switching functions for the surface grid points and originally introduced for the conductor-like screening model (COSMO), are generalized here to an entire class of polarizable continuum models (PCMs). Gaussian blurring of the apparent surface charges proves to be crucial in order to avoid singularities in the reaction-field matrix and spurious oscillations in the energy gradient. The resulting “smooth PCMs” accelerate convergence of geometry optimizations and eliminate spurious peaks in vibrational spectra that are calculated by finite difference of analytic energy gradients.

Monte Carlo Calculations of Reaction Rates and Energy Distributions Among Reaction Products. I. F+H2→HF+H

Abstract: A three‐dimensional, classical trajectory calculation is made of the collision dynamics of the reaction F+H2(v, J)→HF(v′, J′)+H by means of the London‐Eyring‐Polanyi‐Sato (LEPS) potential energy surface. Monte Carlo procedures are used to start each collision trajectory. A discussion is presented of the temperature dependence of the relative rates of formation of vibrationally excited hydrogen fluoride. By means of this calculation, it can be predicted that 71% of the mean fraction of available energy will become vibration in HF, 10.5% will become rotation in HF, and 18.5% will become translation in the product. The probability that direct chemical reaction between atomic fluorine and molecular hydrogen will lead to the formation of the product HF molecule in the ground vibrational state v′=0 was found to be zero. The ratio k(v′=3)/k(v′=2) appears to be independent of temperature and has a value of 0.49, which is in excellent agreement with available experimental data. The ratio k(v′=2)/k(v′=1) has a slig...