Variational bound for the energy of two-dimensional quantum antiferromagnet
Ovchinnikov A. A.
The variational upper bound for the ground-state energy of a two-dimensional antiferromagnetic Heisenberg model on a square lattice for an arbitrary value of the anisotropy parameter was obtained using the two-dimensional generalization of the Jordan-Wigner transformation. The result can be considered as an upper bound for the perturbation theory series about the Ising limit.