Combined nonmetallic electronegativity equalisation and point–dipole interaction model for the frequency-dependent polarisability

Abstract

A molecular mechanics model for the frequency-dependent polarisability is presented. It is a combination of a recent model for the frequency dependence in a charge-dipole model [Nanotechnology 19, 025203, 2008] and a nonmetallic modification of the electronegativity equalisation model rephrased as atom–atom charge-transfer terms [J. Chem. Phys. 131, 044101, 2009]. An accurate model for the frequency-dependent polarisability requires a more accurate partitioning into charge and dipole contributions than the static polarisability, which has resulted in several modifications of the charge-transfer model. Results are presented for hydrocarbons, including among others, alkanes, polyenes and aromatic systems. Although their responses to an electric field are quite different in terms of the importance of charge-transfer contributions, it is demonstrated that their frequency-dependent polarisabilities can be described with the same model and the same set of atom-type parameters.

Keywords:

• atomic charges
• electronegativity equalisation
• point–dipole
• charge-transfer

Acknowledgements

We would like to thank Magnus Ringholm for his contribution to the software development in his master thesis. Support from the Norwegian Research Council through a Strategic Industry Program (164603/I30) and a grant of computer time are acknowledged.

Notes

¹c-DFT polarisability (in-plane component) at ω = 0.1 divided by the corresponding static polarisability

²In the longest possible chain of carbon atoms

³Between the two carbon atoms with the largest separation

1. In atomic units, |e| = 1, ℏ︀ = 1, m _e = 1, 1/4πε₀ = 1. The energy unit 1 hartree is given by , distance unit is 1 bohr given by , frequency is given by and polarisation is given by