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A comprehensive investigation has been made of the spectral excitations and static properties of Heisenberg antiferromagnetic chains of spin 1/2, 1, 3/2, and 2, using Lanczös, Bethe Ansatz, and Monte Carlo techniques. An unusual and unanticipated crossover mechanism for spin chains with 1/2≤S≤∞ has been discovered. The validity of the Haldane conjecture concerning the presence of a spectral excitation gap for integer‐spin chains has been investigated by exact finite chains calculations of (a) the primary singlet‐triplet excitation gap, (b) higher excitation gaps, and (c) the Fourier transform of the ground statecorrelation functions. A new Monte Carlo method has extended the spin‐1 gap calculations to N=32.

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Copyright 1985 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.

The following article appeared in Journal of Applied Physics and may be found at