Hubbard dimer physics and the magnetostructural transition in the correlated cluster material Nb3Cl8

We present a combined computational and experimental study of Nb 3 Cl 8 , a correlated layered material containing Nb trimers, through the lens of competing intra- and intercluster interactions. Different proposed explanations for its magnetostructural transition, such as charge disproportionation, antiferromagnetic quenching, and interlayer singlet formation, are investigated in light of the various reported low-temperature structures. Our findings rule out the previously proposed charge-disproportionation, suggest an intricate interplay between Mott physics and the formation of interlayer singlets, and also hint at a possible explanation of the observed intratrimer scissoring distortion. We suggest that the physics of Nb 3 Cl 8 should be understood in the context of weakly coupled Hubbard dimers.