Intermolecular interactions Coulombic potential energy

What Do We Need to Know Already This chapter uses the concepts of potential energy (Section A), coulombic interactions (Section 2.4), polar molecules and dipoles (Section 3.3), and intermolecular forces in gases (Section 4.12). 

All interionic and almost all intermolecular interactions can be traced to the coulombic interaction between two charges (Section 2.4), and throughout the discussion of intermolecular interactions we shall build on Eq. 5 from Section A, the expression for the potential energy Ef of two charges qx and q1 separated by a distance r ... 

A key to both methods is the force field that is used,65 or more precisely, the inter- and possibly intramolecular potentials, from which can be obtained the forces acting upon the particles and the total energy of the system. An elementary level is to take only solute-solvent intermolecular interactions into account. These are typically viewed as being electrostatic and dispersion/exchange-repulsion (sometimes denoted van der Waals) they are represented by Coulombic and (frequently) Lennard-Jones expressions ... 

The driving force for diffusion is the thermal energy, fcB T, associated with Brownian motion. By contrast, for reactions between ions of charges zAe and zBe, the direct intermolecular potential energy becomes very important and is the Coulomb interaction... 

The multidimensional potential energy surface was written as the sum of a gas-phase (LEPS) energy surface incorporating the main features of the one-dimensional double-well potential in Example 10.1, solvent-solute interactions described by Lennard-Jones potentials with added (Coulomb) interactions corresponding to point charges, and solvent solvent interactions including intermolecular degrees of freedom. The solvent consisted of 64 water molecules. 

The origins of intermolecular attractions are less obvious, and several mechanisms can contribute. First, consider the electrostatic interaction of two rigid charge distributions A and B. By Coulomb s law, the electrostatic potential energy of interaction W(el) is ... 

This contribution to the total molecule/surface interaction is caused by the Coulomb interaction between the charge distributions of the ionic crystal and the adsorbed molecule or, stated differently, by the potential energy of the adsorbed molecule in the electrostatic field above the solid surface. In the theory of intermolecular forces, this interaction is generally expressed by means of a multipole expansion... 

MD simulations of electrolytes for lithium batteries retain the atomistic representation of the electrolyte molecules but do not treat electrons explicitly. Instead the influence of electrons on intermolecular interactions is subsumed into the description of the interatomic interactions that constitute the atomistic potential or force field. The interatomic potential used in MD simulations is made up of dispersion/ repulsion terms. Coulomb interactions described by partial atomic charges, and in some cases, dipole polarizability described by atom-based polarizabilities. The importance of explicit inclusion of polarization effects is considered below. In the most accurate force fields, interatomic potentials are informed by high-level QC calculations. Specifically, QC calculations provide molecular geometries, conformational energetic, binding energies, electrostatic potential distributions, and dipole polarizabilities that can be used to parameterize atomic force fields. 

The intermolecular potential energy between atomic sites can be calculated by a sum of the Coulomb electrostatic interaction and the Lennard-Jones potential ... 

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