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.

Thermodynamic integration of the free energy along a reaction coordinate in Cartesian coordinates

Abstract: A generalized formulation of the thermodynamic integration (TI) method for calculating the free energy along a reaction coordinate is derived. Molecular dynamics simulations with a constrained reaction coordinate are used to sample conformations. These are then projected onto conformations with a higher value of the reaction coordinate by means of a vector field. The accompanying change in potential energy plus the divergence of the vector field constitute the derivative of the free energy. Any vector field meeting some simple requirements can be used as the basis of this TI expression. Two classes of vector fields are of particular interest here. The first recovers the conventional TI expression, with its cumbersome dependence on a full set of generalized coordinates. As the free energy is a function of the reaction coordinate only, it should in principle be possible to derive an expression depending exclusively on the definition of the reaction coordinate. This objective is met by the second class of vector fields to be discussed. The potential of mean constraint force (PMCF) method, after averaging over the unconstrained momenta, falls in this second class. The new method is illustrated by calculations on the isomerization of n-butane, and is compared with existing methods.

Structure and Stability of the Water−Graphite Complexes

Abstract: The interaction of the water molecule with benzene, polycyclic aromatic hydrocarbons, graphene, and graphite is investigated at the density-functional/coupled-cluster (DFT/CC) level of theory. The accuracy of the DFT/CC method is first demonstrated by a comparison of the various interaction energies on the potential energy surface of water−benzene, water−naphthalene, and water−anthracene complexes with the data calculated at the coupled-cluster level at the basis set limit. The potential energy surface of water−graphene and water−graphite is relatively flat with diffusion barriers of about 1 kJ/mol. The structure with both hydrogen atoms of water pointing toward the graphene plane (denoted as a circumflex structure) above the center of the six-member ring is the global minimum characterized with an electronic interaction energy of −13 and −15 kJ/mol for graphene and graphite, respectively. The OH···π complexes (with one OH pointing toward the surface and the other OH being oriented along the surface) are ...