Solid-state systems metal chains

The highly conductive class of solids based on TTF—TCNQ have less than complete charge transfer ( 0.6 electrons/unit for TTF—TCNQ) and display metallic behavior above a certain temperature. However, these solids undergo a metal-to-insulator transition and behave as organic semiconductors at lower temperatures. The change from a metallic to semiconducting state in these chain-like one-dimensional (ID) systems is a result of a Peierls instability. Although for tme one-dimensional systems this transition should take place at 0 Kelvin, interchain interactions lead to effective non-ID behavior and inhibit the onset of the transition (6). 

It is important to recognize the solid-state counterpart of the above observations. Consider a one-dimensional (ID) chain with one electron and one orbital per site (Fig. 26.5a). If electron-electron repulsion is neglected, the levels of the bottom half of the band are each doubly filled, thereby leading to a metallic state (Fig. 26.5b). Non-spin-polarized electronic band structure calculations predict that a system with a half-filled... 

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