LAUSR

In this work, we benchmark the accuracy of the density‐functional tight‐binding (DFTB) method, namely the long‐range corrected second‐order (LC‐DFTB2) and third‐order (DFTB3) models, for predicting energetics of imidazolium‐based ionic liquid (IL) ion pairs. We compare the DFTB models against popular density functionals such as LC‐ωPBE and B3LYP, using ab initio domain‐based local pair‐natural orbital coupled cluster (DLPNO‐CC) energies as reference. Calculations were carried out in the gas phase, as well as in aqueous solution using implicit solvent methods. We find that the LC‐DFTB2 model shows excellent performance in the gas phase and agrees well with reference energies in implicit solvent, often outperforming DFTB3 predictions for complexation energetics. Our study identifies a range of opportunities for use of the LC‐DFTB method and quantifies its sensitivity to protonation states and the types of chemical interactions between ion pairs.