One-Dimensional Chain of Anisotropic Spin-Spin Interactions. II. Properties of the Ground-State Energy Per Lattice Site for an Infinite System
The ground-state energy 2f per lattice site for an infinite system is studied as a function of Δ and of the magnetization y. Analyticity properties of f(Δ, y) are proved. The behavior of f(Δ, y) at and near y=0 and y=1 are investigated.