Giant Kohn anomaly

The Peierls transition and the giant Kohn anomaly are driven by the divergence of the polarization function x( ) for q = 2kp. Conditions for the divergence are understood intuitively in terms of the nesting of the Fermi surface Figure 20 shows the three dimensional representation of the Fermi surfaces of one- and two-dimensional electron systems. The divergence of xiq) at T = 0 is considered to be ascribed to the condition, - E = 0 stnd f E -f (E + q) 0. It is... 

In one-dimensional metals, the electron-phonon interaction produces much stronger Kohn anomalies than in three-dimensional metals. In fact, a giant Kohn anomaly has been observed in the one-dimensional conductor KCP [1.35]. For a more detailed discussion of the theory of phonons in metals, the reader is referred to [4.66] and to the work by HARRISON [4.71] in which the pseudopotential approximation is used. This latter method yields good agreement between calculated and observed phonon frequencies of simple metals such as aluminium with only two model parameters. 

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