Many-body ab initio study of antiferromagnetic {Cr_7 M} molecular rings

摘要

Antiferromagnetic molecular rings are widely studied both for fundamental quantum-mechanical issues and for technological applications, particularly in the field of quantum information processing. Here we present a detailed first-principles study of two families- purple and green-of {Cr_7 M} antiferromagnetic rings, where M is a divalent transition metal ion (M = Ni~(2+), Mn~(2+), and Zn~(2+)). We employ a recently developed flexible and efficient scheme to build ab initio system-specific Hubbard models. From such many-body models we systematically derive the low-energy effective spin Hamiltonian for the rings. Our approach allows us to calculate isotropic as well as anisotropic terms of the spin Hamiltonian, without any a priori assumption on its form. For each compound we calculate magnetic exchange couplings, zero-field splitting tensors, and gyromagnetic tensors, finding good agreement with experimental results.