Electrostatic potential, molecular interactive computation

The macroscopic property of interest, e.g., heat of vaporization, is represented in terms of some subset of the computed quantities on the right side of Eq. (3.7). The latter are measures of various aspects of a molecule s interactive behavior, with all but surface area being defined in terms of the electrostatic potential computed on the molecular surface. Vs max and Fs min, the most positive and most negative values of V(r) on the surface, are site-specific they indicate the tendencies and most favorable locations for nucleophilic and electrophilic interactions. In contrast, II, a ot and v are statistically-based global quantities, which are defined in terms of the entire molecular surface. II is a measure of local polarity, °fot indicates the degree of variability of the potential on the surface, and v is a measure of the electrostatic balance between the positive and negative regions of V(r) (Murray et al. 1994 Murray and Politzer 1994). 

The first step in our procedure is to compute an optimized structure for each molecule and then to use this geometry to compute the electronic density and the electrostatic potential. A large portion of our work in this area has been carried out at the SCF/STO-5G //SCF/STO-3G level, although some other basis sets have also been used. We then compute V(r) on 0.28 bohr grids over molecular surfaces defined as the 0.001 au contour of the electronic density (Bader et al. 1987). The numbers of points on these grids are converted to surface areas (A2), and the and Fs min are determined. Our statistically based interaction in-... 

The use of the electrostatic potential in analyzing and predicting molecular interactive behavior and properties has increased remarkably over the past 25 years. In 1980, it was still reasonable to hope to at least mention, in one lengthy review chapter (Politzer and Daiker 1981), all of the papers that had been published in this area. In 1996, such an objective would be ridiculous. This popularity can be attributed to (a) the insight that V(r) can provide, especially into noncovalent interactions, and (b) the widespread availability of computational software packages of which it has become a standard feature. 

Different solvation methods can be obtained depending on the way the (Vs(r p)) xj tern1 is calculated. So, for instance, in dielectric continuum models ( Vs(r p)) x is a function of the solvent dielectric constant and of the geometric parameters that define the molecular cavity where the solute molecule is placed. In ASEP/MD, the information necessary to calculate Vs(r, p))[Xj is obtained from molecular dynamics calculations. In this way (Vs(r p))[Xj incorporates information about the microscopic structure of the solvent around the solute, furthermore, specific solute-solvent interactions can be properly accounted for. For computational convenience, the potential Vs(r p)) X is discretized and represented by a set of point charges, that simulate the electrostatic potential generated by the solvent distribution. The set of charges, is obtained in three steps [26] ... 

Higher + Electronic + Interaction with the environment Spatio-temporal structure (flexibility, conformation) Electronic properties (electron distribution, polarizability, ionisation) Solvation, hydration, partitioning, intermolecular interactions Conformational energy diagrams, computer display Molecular orbitals, electrostatic potential maps Computer display... 

Here, we report, for the first time, ab initio computations of the six lowest-lying electronic states of Na2" ". These computations utilize the basis set developed to describe the low-lying states of the neutral Nap, molecules (6) and utilize integrals which have been computed previously (, ). The molecular energies computed at the single-configuration self-consistent-field (SC-SCF) level are listed in Table I. These SC-SCF computations should provide relatively reliable potential curves for what are effectively one-electron systems. We do not attempt to describe the electron correlation associated with the core electron motions nor that associated with the polarization of the core electrons by the single valence electron. Thus, while dispersion effects are not well described, the first order ion-induced dipole Interaction and the major electrostatic interactions of the valence electron are probably reasonably well described at the SC-SCF level. Note in Table II, where we list molecular constants for Nap, that the 1 state is bound. Its 1 T. counterpart in the neutral molecule is predicted to be... 

Recently, detailed molecular pictures of the interfacial structure on the time and distance scales of the ion-crossing event, as well as of ion transfer dynamics, have been provided by Benjamin s molecular dynamics computer simulations [71, 75, 128, 136]. The system studied [71, 75, 136] included 343 water molecules and 108 1,2-dichloroethane molecules, which were separately equilibrated in two liquid slabs, and then brought into contact to form a box about 4 nm long and of cross-section 2.17 nmx2.17 nm. In a previous study [128], the dynamics of ion transfer were studied in a system including 256 polar and 256 nonpolar diatomic molecules. Solvent-solvent and ion-solvent interactions were described with standard potential functions, comprising coulombic and Lennard-Jones 6-12 pairwise potentials for electrostatic and nonbonded interactions, respectively. While in the first study [128] the intramolecular bond vibration of both polar and nonpolar solvent molecules was modeled as a harmonic oscillator, the next studies [71,75,136] used a more advanced model [137] for water and a four-atom model, with a united atom for each of two... 

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