A halogen-bonding correction for the semiempirical PM6 method

We analyse the failure of the semiempirical QM method PM6 to describe halogen bonds and suggest an empirical correction that remedies this problem. Owing to underestimated repulsion in the PM6 method, the halogen-bond interaction energies are dramatically exaggerated and the equilibrium distances are very short. This is addressed by a correction parametrised for all halogens capable of halogen bonding (Cl, Br, and I). The correction is applied on top of the dispersion correction, forming the PM6-D2X method. A comparison with ab initio calculations shows that the method is able to predict the interaction energy of halogen bonds with an error of 10%.