We investigate the electronic structure and magnetic properties of the distorted honeycomb lattice compound KCuIn(PO 4 ) 2 through a combination of experimental measurements, first‐principles calculations and quantum monte‐carlo simulations. Density‐functional theory calculations within the GGA + U framework establishes KCuIn(PO 4 ) 2 as an indirect‐gap insulator with Cu 2+ () local moments and finite magnetocrystalline anisotropy arising from spin‐orbit coupling. A microscopic evaluation of magnetic exchange interactions using the magnetic force theorem reveals a pronounced hierarchy of couplings, with the next–nearest‐neighbor (NN) interaction dominating over the NN exchange, while interlayer couplings remain negligible. This exchange hierarchy naturally maps the system onto weakly coupled antiferromagnetic spin chains embedded in a distorted honeycomb lattice. Motivated by the ab initio estimated exchange interactions, we construct an effective spin‐ Hamiltonian and investigate its magnetic response using large‐scale quantum Monte Carlo simulations. The calculated temperature‐dependent susceptibility and field‐dependent magnetization quantitatively reproduce the experimental behavior and capture key signatures of low‐dimensional quantum magnetism, including a broad susceptibility maximum and a field‐induced saturation at low temperatures. Our results establish KCuIn(PO 4 ) 2 as a quasi‐two‐dimensional quantum antiferromagnet composed of coupled spin chains, providing a consistent theoretical framework that links electronic structure, exchange interactions, and collective magnetic behavior.
Gayen et al. (Wed,) studied this question.