= Isotropic spin-wave vacuum energy comparison
The polarized <ground state> of an isotropic <Heisenberg model> with ferromagnetic exchange is an exact state. Its normal-ordered harmonic <Hamiltonian> has no pair-creation terms, no vacuum magnon occupation and no additional zero-point shift. An antiferromagnetic <Néel state> instead generates anomalous terms, a squeezed <Bogoliubov transformation> vacuum, a negative energy correction and reduced staggered magnetization. Neither statement licenses omitting normal-ordering constants from an arbitrary spin-wave model with anisotropy or a different reference state.
Back to article page
