To understand the origin of the observed low-dimensional interactions we carried out collinear spin-polarized plane-wave density-functional theory (DFT) calculations, by exploring the electronic structure of the DFT ground-state spin configuration and calculating the exchange energies using the broken symmetry approach. We first optimised the geometry of the experimental structure using the PBE functional along with a many-body semi-empirical dispersion correction (MBD*) to describe the weak van der Waals forces between the layers. We found that this structure was both too dense, with a unit-cell volume of 297.68 Å 3 , 4.8% smaller than experimental value of 312.75 Å 3 , and lacked the JT distortion characteristic of Cr(II). We therefore included an effective Coulomb on-site energy, U eff = U -J where U is the on-site repulsion and J the exchange energy, to account for the overly delocalised Cr d-states. A range of values for U eff have been previously explored for Cr, from U eff = 2.1 eV to U eff = 3.5 eV. We found that U eff = 3 eV was able to accurately capture the physics of this system, and produced a structure with both a JT distortion and, as a bonus, a volume within +0.2% of experiment.