Polarization function sets, intermolecular

The first two rows of Table 1 make readily apparent the poor suitability of both ST0-3G and 3-21G for H-bonds the intermolecular R(00) distance is some 0.2 A too short. The 6-31G(d) set (also known as 6-31G" ) contains a better representation of the inner shells as well as polarization functions on O. The SCF distance of 2.971 A computed with this basis set is a substantial improvement over those from the smaller basis sets, STO-3G and 3-21G. Further improvements in the basis set make relatively minor changes in this distance. For example, addition of p-functions to H elongates the bond by 0.009 A, whereas augmentation of O by -f- functions (a diffuse sp-shell) reduces the distance by 0.007 A. It is instructive to note that the latter two effects are not additive. That is, one might naively expect a net bond elongation of 0.002 A to result from incorporation of both H p-functions and O -F functions by addition of the two latter effects. However, the 6-31 -F G(d,p) R (OO) distance reported in Table 1 is 2.988 A, 0.017 A longer than the 6-31G(d) value. 

The presence of an additional benzene ring in 5,6-benzo-4 -A, Af-diethyl-amino-3-hydroxyflavone (16, Fig. 9) inhibits intermolecular hydrogen bond formation with protic solvents, yet allowing, at the same time, the photo-induced intramolecular proton transfer with the hydroxyl group. These properties permitted to set up a linear correlation of the log (Iin/Iit) value with the solvent polarity function (f(s)) that could be extended to all of the examined solvents, contrary to the case of parent 9, where only a correlation with aprotic media was found. ... 

It is also necessary to include electron correlation in any accurate calculation of intermolecular interactions, since the dispersion interaction is a correlation effect, and is usually an important component of the interaction energy. Moreover the dispersion interaction describes correlated fluctuations of the charge distributions in the two molecules, and this calls for an accurate description of the molecular polarizability, which in turn requires a large basis set containing a large number of diffuse polarization functions. 

DPT calculations are not suitable for evaluating the inter molecular interactions of aromatic molecules, as dispersion is the major source of the attraction in the interactions of aromatic molecules, with the exception of cation/TT interactions. DPT calculations using basis sets with polarization functions provide sufficiently accurate intermolecular interaction energies for the cation/TT interactions, as DPT calculations can reproduce electrostatic and induction energies sufficiently accurately. 

A general method of predicting the effective molecular diameters and the thermodynamic properties for fluid mix-tures based on the hard-sphere expansion conformal solution theory is developed. The method of Verlet and Weis produces effective hard-sphere diameters for use with this method for those fluids whose intermolecular potentials are known. For fluids with unknown potentials, a new method has been developed for obtaining the effective diameters from isochoric behavior of pure fluids. These methods have been extended to polar fluids by adding a new polar excess function, to account for polar contributions in a mixture. A new set of pseudo parameters has been developed for this purpose. The calculation of thermodynamic properties for several fluid mixtures including CH —C02 has been carried out successfully. 

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