Copper acetate monohydrate in the extended Hubbard dimer model

Dimeric compounds with their antiferromagnetically coupled pairs of spins have been of fundamental interest in solid-state magnetism during the past century, recently revived by the discovery of their bosonic state with a high-temperature quantum phase transition [1]. Experimentally, the exchange coupling between dimeric atoms can be unambiguously probed by inelastic neutron scattering (INS). In this work, we calculate the ground-state electronic structure of the prototypical dimer copper acetate monohydrate and derive its INS spectra, which directly expose the atomic spin density in this prototypical system. We also show that the molecule can be accurately represented within an extended Hubbard dimer model. Ab initio parametrization [2] of the model then reveals a significant direct exchange contribution besides the dominating superexchange. The resulting singlet-triplet splitting is in excellent agreement with the experiment. 

[1] R. Calvo, et al., Coordination Chemistry Reviews 480, 215007 (2023).

[2] V. V. Mazurenko, et al., Phys. Rev. B 75, 224408 (2007).