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Using an intermolecular potential from ab initio calculations, we have calculated the structure and solved the lattice dynamics problem of the ethylene crystal in the self‐consistent phonon formalism. The anharmonic effects, as included by this formalism, systematically improve the optical mode frequencies, in comparison with experiment, but the corrections to the harmonic frequencies are still substantially too small. The crystal structure and its pressure dependence are well represented. From the phonon polarization vectors we have also evaluated the Raman scattering and infrared absorption intensities of the optical modes, applying a scheme which takes into account the mutual polarization of the molecules (the ’’local field corrections’’). The Raman intensities agree quite well with experiment; the infrared intensities are less realistic, probably due to the neglect of intermolecular overlap effects in the intensity calculations. Using an empirical atom–atom potential for hydrocarbons instead of the ab...

the journal of chemical physics

Dynamical and optical properties of the ethylene crystal: Self-consistent phonon calculations using an ‘‘a b i n i t i o’’ intermolecular potential