Electronic structure of Na2CuP2O7: a nearly 2D Heisenberg antiferromagnetic system

We have employed first principles calculations to study the electronic structure and the implications for the magnetic properties of Na2CuP2O7. Using the self-consistent tight-binding linearized muffin-tin orbital method and the Nth-order muffin-tin orbital downfolding method, we have calculated the various intrachain and interchain hopping parameters between the magnetic Cu2+ ions. Our calculations for Na2CuP2O7 reveal dominant intrachain hopping, but in contrast to the typical quantum spin chains the interchain hoppings are not negligible. The Wannier function plot of the Cu dx2-y2 orbitals shows that the exchange interactions are primarily mediated by the oxygens and the distance between the oxygens in Na2CuP2O7 is favorable for both intrachain and interchain interactions, suggesting the inapplicability of the one-dimensional Heisenberg model for this system, in agreement with recent experimental results.