Triple-dipole dispersion energy

Hence, the same teclmiques used to calculate are also used for Cg. Note that equation (A1.5.28) has a geometrical factor whose sign depends upon the geometry, and that, unlike tlie case of the two-body dispersion interaction, the triple-dipole dispersion energy has no minus sign in front of the positive coefficient Cg. For example, for an equilateral triangle configuration the triple-dipole dispersion is repulsive and varies... 

Kumar A, Meath WJ (1985) Pseudo-spectral dipole oscillator strengths and dipole-dipole and triple-dipole dispersion energy coefficients for HF, HC1, HBr, He, Ne, Ar, Kr and Xe. Mol Phys 54 823-833... 

The simplest model for the three-body dispersion energy is provided by the well-known triple-dipole expression... 

McDowell SAC, Kumar A, Meath W1 (1996) Anisotropic and isotropic triple-dipole dispersion energy coefficients for all three-body interactions involving He, Ne, Ar, Kr, Xe, H2, N2, and CO. Canad J Chem 74 1180-1186... 

The other non-additive effect which has attracted most attention is the Axilrod-Teller triple-dipole dispersion energy, which for three atoms or rotationally-averaged molecules A, B and C is[30]... 

From a detailed examination of the three-body SAPT energies for the argon liquid, Bukowski et al. (Bukowski and Szalewicz 2001) have concluded that the bulk of the three-body dispersion energy can be estimated using the AxUrod-Teller-Muto triple dipole term. For isotropic local distributed polarizabihties this takes the form (Stone 1996)... 

For N, there is a sizeable triples contribution to the lowest dipole allowed excitation energy of about 0.07 eV or 0.7%. As a consequence of tliis (unrelaxed) CCSD underestimates the absolute value of the isotropic hyperpolarizability and its dispersion. Tire electronic contribution to the static limit y - has been calculated at the CCSD/t-aug-cc-pVTZ level [32] to be 903.0 a.u. However, as indicated above, the triple- level is often too low for the calculation of second hyperpolarizabilities and the yj obtained at the CCSD/t-aug-cc-pVTZ level turned out to be about 40 a.u. above the CCSD basis-set limit result. Tlie latter has been calculated to be 863.3 3.3 a.u. [35]. Before comparing this result to tlie value extrapolated from experimental results, it has to be corrected for the ZPV contribution, which has been obtained in [32] to 12.0 a.u., thereby yielding 875.3 3.3 a.u. as tlie best estimate for the electronic contribution to y at the CCSD level. Shelton [6] obtained an experimental value of yj , 917 9 a.u., from the extrapolation of tlie results in [2] corrected for the pure rotational and vibrational contributions. Tire discrepancy between this experimental value and the CCSD best estimate is as large as 42 a.u. and makes very clear the importance of tire triples contribution. 

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