The polarizabilities of CH and CC bonds

Abstract

A variant of uncoupled Hartree-Fock perturbation theory is described which uses as zero-order function a Hartree-Fock wavefunction built up from localized orbitals. The second-order energy has the form of a sum of contributions from the individual orbitals which. since the orbitals are typically localized along bonds, can be interpreted as the sum of bond contributions. A variational procedure for computing these bond contributions is derived and applied to finding the components of the electric polarizability tensor for the CH and CC bonds in the molecules methane. ethane, ethylene. and acetylene.

Absolute Raman intensities, force constants, and electro-optical parameters of CH2Cl2, CD2Cl2 and CHDCl2

“…Using F(CHC13) = -2.7 A 3 [24,29] and F(CHC13) = [(7 -a)cn -1"06(7 -00eel ] we find (7'-a)CCl= 2"55 + 0"94(7-00cri. No agreement is found in the literature with respect to the sign of (7-a)ca [30][31][32][33] although it is generally accepted that its absolute value is small. Thus we would conclude the following: -0.5 ~< (7 -a)cr~ ~< 0'5 and 2.1 ~< (y -a)ccJ ~< 3.0.…”

Ab initiocalculations of multipole moments, polarizabilities and long-range interaction coefficients for the azabenzene molecules

“…Even for the long range interactions, which can be treated on the basis of monomer multipole properties, the computations are very hard. Especially the accurate calculation of multipole polarizabilities requires an extended AO basis set, including atomic polarization functions [31][32][33][34]. This equally affects the recent CNDO calculations of the dipole polarizabilities of some of the azabenzene molecules [35][36][37] which are, to our knowledge, the only quantum chemical calculations available for these properties.…”

Ab initio Studies of long range interactions between ethylene molecules in the multipole expansion

“…Employing an interaction operator containing all dipole, quadrupole and octupole interactions, one obtains multipole terms with maximum R~ 14 dependence. However, only the CfJ'sp and Cg,sp terms are complete: for example, missing non-zero cross terms in C 1 are arising from (11,24) and (11,15) interactions. Moreover, to be consistent, one should include also higher order perturbation effects, because these give rise to non-vanishing terms which start oiT with an R 11 dependence (a third order contribution).…”

“…A similar approach has been adopted in our analysis of the He2 interaction energy [18], where optimal exponents were computed for the p and cl polarization func tions on He using the multipole expansion, which were then used in VB calcula tions. The importance of polarization functions has been stated previously for first order molecular properties like permanent multipole moments [19][20][21] as well as for second order properties like polarizabilities [22][23][24][25]; their necessity for the interaction energy has also been stressed by several authors [18,[26][27][28]. In the present paper two criteria are applied to judge on the adequacy of the AO basis: the first, which compares the permanent moments on the monomers with the best available data, gives an estimate for the reliability of the computed first order (electrostatic) energy.…”