Combinatorial exploration of herbertsmithite-related quantum spin liquid candidates

Geometric frustration of magnetic ions can lead to a quantum spin liquid (QSL) ground state, where long range magnetic order is avoided despite strong exchange interactions. The highly degenerate ground state that results can give rise to exotic properties, and the physical realization of QSLs comprises a major unresolved area of contemporary condensed matter physics. One such magnetically frustrated structure is the kagome lattice. Herbertsmithite [ZnCu₃(OH)₆Cl₂] and Zn-barlowite [ZnCu₃(OH)₆BrF] feature pristine kagome layers of copper ions, and display experimental signatures of a QSL state at low temperatures. To investigate other possible QSL candidates, we perform a systematic first-principles combinatorial exploration of structurally related compounds [ACu₃(OH)₆B₂ and ACu₃(OH)₆BC] by substituting cations A (with Ba, Be, Ca, Cd, Ge, Hg, Mg, Pb, Sn, Sr, and Zn) and anions B/C (with Br, Cl, F, and I). After optimizing such structures using density functional theory, we compare structural and thermodynamic parameters to determine which compounds are likely to host QSL phases. Pseudo-convex hull calculations using binary compounds are performed to determine feasibility of synthesis. We also estimate the likelihood of interlayer substitutional disorder and spontaneous distortions of the kagome layers. After considering all of these factors, we select promising candidate members of the herbertsmithite and Zn-barlowite families that may host QSL ground states and merit further attention.