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Analysis of molecular polarizabilities and polarizability derivatives in H 2 , N 2 , F 2 , CO, and HF, with the theory of atoms in molecules

1996; NRC Research Press; Volume: 74; Issue: 6 Linguagem: Inglês

10.1139/v96-128

1480-3291

Kathleen Gough, Margaret M. Yacowar, Richard H. Cleve, Jason R. Dwyer,

Chemical Thermodynamics and Molecular Structure

Ab initio molecular orbital calculations have been performed on the title molecules at the SCF-HF and MP2 levels to obtain molecular polarizabilities and the derivatives associated with bond stretch. The wave functions from these calculations have been analyzed with the theory of atoms in molecules (AIM). Both the polarizability and its derivative are successfully reconstructed from AIM terms representing the transfer of charge between atoms (CT = charge transfer) and the rearrangement of charge within an atomic basin (AD = atomic dipole). The results for the diatomics are compared to each other and to the alkanes studied previously. Equilibrium polarizabilities are qualitatively explained with reference to atomic electronegativity and type of bonding. While derivatives of the mean molecular polarizability differ by a factor of two at most, individual contributions vary by an order of magnitude. The derivatives along the bond axis for H 2 are ΔCT = 2.06 and ΔAD = −0.62 × 10 −30 C m/V, while for N 2 they are ΔCT = 13.77 and ΔAD = −10.00 × 10 −30 C m/V. The common feature observed is that as the induced dipole due to charge transfer increases, the induced dipole due to changes in the atomic dipole also increases and opposes it. Key words: diatomic molecules, molecular polarizability, molecular polarizability derivative, theory of atoms in molecules, ab initio molecular orbital calculations.