Electron charge orderings and Peierls distortion

An extension of the quasi one-dimensional spinless fermion model is discussed, involving, besides electron-electron interactions, also two types of electron-lattice coupling. For the case of one-half electron per site, three types of ordering are possible in the system under consideration: (i) a charge ordered state characterized by a disproportionation of the electron density at the crystal sites accompanied, in the presence of electron-optical phonon coupling, by static internal distortion, (ii) a charge ordered state characterized by a disproportionation of the electron density on the bonds accompanied by dimerization of the lattice - Peierls type distortion, (iii) a mixed state involving both types of the electron orderings and distortions. Within the Hartree-Fock approximation the properties of these orderings at T=0 as well as T>0 are analyzed and the ground state stability of the ordered phases is determined. (author)