Is Solid Copper Oxalate a Spin Chain or a Mixture of Entangled Spin Pairs?

Abstract

Macroscopic assemblies of interacting spins give rise to a broad spectrum of behaviors determined by the spatial arrangement of the magnetic sites and the electronic interactions between them. Compounds of copper­(II), in which each copper carries spin 1/2, exhibit a vast variety of physical properties. For antiferromagnetically coupled spin sites, there are two limiting scenarios: spin chains in which the spins can exhibit a long-range order or a mixture of dimers in which the spins within each pair are entangled but do not interact with the spins from other dimers. In principle, the two types can be distinguished on the basis of experimental observations and modeling using empirically parameterized effective Hamiltonians, but in practice, ambiguity may persist for decades, as is the case for copper oxalate. Here, we use high-level ab initio calculations to establish the validity of the nearest-site Heisenberg model and to predict the interaction strength between the magnetic sites. The computed magnetic susceptibility provides an unambiguous interpretation of magnetic experiments performed over half a century, clearly supporting the infinite spin-chain behavior of solid copper oxalate.

Equation-of-Motion Coupled-Cluster Protocol for Calculating Magnetic Properties: Theory and Applications to Single-Molecule Magnets

“…Finally, we determined that using a larger basis set, that is, cc-pVTZ, has a very small effect on the energy barrier U and on the computed magnetization and susceptibility data (deviations are about 10 cm –1 for U and within 1% for the average magnetization and susceptibility, see Figure S11 and Table S5 in the SI). This almost negligible dependence on the size of the basis set is in line with the previous results for bicopper compounds and copper oxalate chains. , …”

Interpretation of multiple solutions in fully iterative GF2 and GW schemes using local analysis of two-particle density matrices

“…The increase in |J| from UHF to GW is consistent with the previous theoretical calculations. The significant role of weak correlation is not unique to this iron example and has been observed before [96,104].…”

“…where S, T, and BS denote the singlet, triplet, and broken-spin solutions. Such construction of effective Hamiltonian is different from the Bloch's effective Hamiltonian theory [86][87][88], also used for derivations of the effective magnetic Hamiltonians [89][90][91][92][93][94][95][96].…”

Magnetic Exchange Interactions in Binuclear and Tetranuclear Iron (III) Complexes Described by Spin-Flip DFT and Heisenberg Effective Hamiltonians

“…Hamiltonians. Such an approach can even be applied an infinite number of spins, as was recently illustrated for spin chains in solid copper oxalate [33] and for extended conjugated carbon-based molecules with polyradical character [59].…”

“…We follow an alternative strategy based on the spin-flip approach. Spin-flip (SF) methods [21][22][23][24][25][26][27] offer a balanced treatment of multi-configurational states of polyradicals within a single-reference formalism, making the SF-protocol suitable for applications to SMMs [28][29][30][31][32][33]. The SF approach does not rely on scrambled spin-states and does not re-quire choosing an active space.…”