Dimensional effects on the LO-TO splitting in CF4: First-principles and infrared absorption studies

作者：Yim WL; Byl O; Yates JT; Johnson JK^*

来源：Journal of the American Chemical Society, 2005, 127(9): 3198-3206.

DOI：10.1021/ja043540v

The development of longitudinal optical-transverse optical (LO-TO) modes in CF4 has been studied experimentally and theoretically as a function of dimensionality. Infrared absorption experiments for CF4 adsorbed on single-walled carbon nanotubes indicate a lack of LO-TO splitting at low coverage and a gradual appearance of LO-TO modes as the coverage of CF4 on the nanotubes is increased. We have performed density functional perturbation theory calculations for the vibrational frequencies, IR absorption spectra, and phonon density of states for CF4 in one, two, and three dimensions. The calculations demonstrate that LO-TO splitting in 1D is qualitatively different from that computed for 2D or the bulk. The magnitude of the splitting in 1D is about one-half that computed for the bulk, and the LO mode is very weakly blue-shifted in 1D. We predict that the phonon density of states changes dramatically as the dimensionality of the crystal is changed. This prediction can be tested experimentally via inelastic neutron scattering. We conclude that LO-TO splitting can be used as a probe to identify 1D states of matter.

• 出版日期2005-3-9