VARIATIONAL LOCALIZED-SITE CLUSTER EXPANSIONS .10. DIMERIZATION IN LINEAR HEISENBERG CHAINS

Ground-state instability to bond alternation in long linear chains is considered from the point of view of valence-bond (VB) theory. This instability is viewed as the consequence of a long-range order (LRO) which is expected if the ground state is reasonably described in terms of the Kekulé states (with nearest-neighbor singlet pairing). It is argued that the bond alternation and associated LRO predicted by this simple, VB picture is retained for certain linear Heisenberg models; many-body VB calculations on spin s=12 and s=1 chains are carried out in a test of this argument. © 1979 The American Physical Society.