Second-order effects on the interchain and interlayer interactions in low-dimensional electronic systems

The role of second-order perturbations in interchain interactions of one-dimensional electronic systems as well as in interlayer interactions of two-dimensional systems is discussed. The general features of such interchain interactions are deduced from a simpletwo-chain model. It is well known that charge density wave occurring in one-dimensional systems causes preferred structural changes such as dimerization of the nearest neighbor units. From a perturbation-theoretic analysis, the second-order term originating from two different bands in the vicinity of the Fermi level is shown to lead to an important out-of-phase coupling of charge density waves on neighboring chains. The preferred distortion is predicted for various electron counts using a "transition-density" or "transition-force" analysis. The well-known ABAB stacking of layers in natural graphite is rationalized by a transition density analysis to be a consequence of orbital interactions between graphite layers.