Applequist polarizabilities

The singularities can be avoided by making the polarizabilities sufficiently small so that at the typical distances between the atoms (> 1 A) the factor 4aAais/r6 is always less than one. The Applequist polarizabilities are in fact small compared to ab... 

The development of the methods described in Section 9.2 was an important step in modeling polarization because it led to accurate calculations of molecular polarizability tensors. The most serious issue with those methods is known as the polarization catastrophe since they are unable to reproduce the substantial decrease of the total dipole moment at distances close to contact as obtained from ab initio calculations. As noted by Applequist et al. [49], and Thole [50], a property of the unmodified point dipole is that it may originate infinite polarization by the cooperative interaction of the two induced dipoles in the direction of the line connecting the two. The mathematical origins of such singularities are made more evident by considering a simple system consisting of two atoms (A and B) with isotropic polarizabilities, aA and c b. The molecular polarizability, has two components, one parallel and one perpendicular to the bond axis between A and B,... 

Applequist J, Carl JR, Fung K-K (1972) Atom dipole interaction model for molecular polarizability. Application to polyatomic molecules and determination of atom polarizabilities. J Am Chem Soc... 

POL and POLl have the same three-site tetrahedral, SPC-like geometry with a charge on each site. The charge magnitude is adjusted to reproduce properties of the liquid, and the resulting dipole, 2.024 D, is much closer to the value in gas phase than for effective non-polarizable models. Polarizability, described by atomic polarizabilities obtained from the atom-dipole interaction model of Applequist et al [172] is however underestimated. POLl modifies the... 

Applequist, J., Carl, J. R., and Fung, K.-K.,/ A/w. Chem. Soc., 94, 2952, 1972. Excellent reference on the calculation of molecular polarizabilities, including extensive tables of tensor polarizabilities, both theoretical and experimental, at 589.3 nm wavelength. 

For compounds that are transparent in the near-UV region, conformational information may be obtained from the optical rotation at one wavelength. A method that permits the calculation of the optical rotation of a molecule from atom polarizabilities and atom coordinates has been developed by Applequist (1977). The method is based on the interactions between the dipoles that are induced in the atoms by the electric field of the light, and the results are highly sensitive to the geometry of the molecule. Even if the precision of the calculations is moderate, the results may permit distinction between alternative conformers. 

An alternative way of including polarization is by using the ideas developed by Applequist and coworkers.By modifying the dipole operator and assigning point polarizabilities to all atoms, it is possible to generate a self-consistent set of atom polarizabilities for a large number of small molecules. With this approach, the atom polarizabilities are transferable and molecular polarization can be constructed for arbitrary molecules. 

In a simple electrostatic interaction model proposed originally by Silberstein [37] and Applequist [20], the response of an aggregate of atoms (molecule or cluster) to an external electric field can be determined through the atomic dipoles induced at each individual atom as a response to not only the external field buf also an effective field due to the other induced dipoles, which depend on the atomic polarizability parameters. The basic equation of this interaction approach to obtain the polarizability of the aggregate is given by the expression for the induced dipole p at the a-th atomic site, given by... 

J. Applequist, J. R. Carl, and K.-K. Fung,/. Am. Chem. Soc., 94(9), 2952—2960 (1972). An Atom Dipole Interaction Model for Molecular Polarizability Application to Polyatomic Molecules and Determination of Atom Polarizabilities. 

Using the ADIM formulation Applequist and Quicksall [321] have made an attempt to reproduce the experimental d a/dQi and df/dQi quantities in the series of methane and its halogenated derivatives employing five atomic polarizability parameters only. These are da /dR H, 3ap/3R p, 5acj/3Rcci ... 

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