Gm. Mao et al., Generalized anisotropic planar rotor model and its application to polymer intercalation compounds, PHYS REV L, 83(13), 1999, pp. 2588-2591
A diverse structural phase progression is observed in diffraction studies o
f an alkali-metal intercalated conducting polymer, poly(p-phenylene vinylen
e), as functions of both temperature and chemical potential. Despite the pr
esence of translational displacements, extensive disorder, and other experi
mental host limitations, an equivalent heuristic structural counterpart app
ears in a phase diagram derived using a modified anisotropic planar rotor H
amiltonian (introduced and studied by Choi, Harris, and Mele). This model i
ncludes only rotational motions and therefore demonstrates that much of the
underlying structural evolution is governed by only a few key degrees of f
reedom.