First principles perspective on the microscopic model for Cs2CuCl4 and Cs2CuBr4

We investigate the microscopic model for the frustrated layered antiferromagnets Cs(2)CuCl(4) and Cs(2)CuBr(4) by performing ab initio density functional theory (DFT) calculations and with the help of the tight-binding method. The combination of both methods provide the relevant interaction paths in these materials, and we estimate the corresponding exchange constants. We find for Cs(2)CuCl(4) that the calculated ratio of the strongest in-plane exchange constants J'=J between the spin-1/2 Cu ions agrees well with neutrons cattering experiments. The microscopic model based on the derived exchange constants is tested by comparing the magnetic susceptibilities obtained from exact diagonalization with experimental data. The electronic structure differences between Cs(2)CuCl(4) and Cs(2)CuBr(4) are also analyzed.