Slater-Kirkwood approximation

The Slater-Kirkwood equation (Eq. 39) was selected with N = 4 for carbon and N = 1 for hydrogen. The success of the equivalent calculation for the intermolecular interaction of CH4 molecules was mentioned in the previous section. Atoms, rather than bonds, were chosen as the basis for the calculation because the location of the atom centers is unambiguous and the approximation of isotropic polarizability is better for an atom than for a bond. Possible deviations from isotropic polarizability are discussed in Section V. Ketelaar19 gives for the atomic polarizabilities of hydrogen and carbon a = 0.42 and 0.93x 10-24 cm3, respectively. The resulting equation for the London energy is... 

Because the values of and V2 are not easily available, one seeks other ways to estimate the dispersion constant C from readily measurable molecular properties. One very good approximate expression, which was developed by Slater and Kirkwood (20], can be written as... 

Alternative approximations have been given by Slater and Kirkwood and by Neucebauer leading to somewhat different (mostly higher) numerical values. 

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