for developing the charge order state. Further model calculations try to take the temperature and an interchain interaction into account. The extended Hubbard model for a single chain including inter-site and on-site interaction V and U as well as the parameter for a small dimerization which can be typically found in the (TMTTF)₂X compounds is presented as follows:

where t describes the transfer integral or the kinetic energy of the electron and and are the creation and annihilation