Instability of the uniform antiferromagnetic chain. II. Heisenberg interaction in the Hartree‐Fock approximation

We consider a linear antiferromagnetic chain of elastically coupled spins in the Hartree‐Fock approximation to the Heisenberg Hamiltonian. The nuclear dynamics is neglected. The instability of the system is investigated and the results are compared with the X‐Y model treated in I. It is shown that the Hartree‐Fock approximation is essentially equivalent to a renormalization of the exchange integral in the X‐Y model.