The QUantum Interaction Computational Kernel (QUICK) program is an open-source, GPU enabled, ab initio and density functional theory program, which has been developed for QM and QM/MM calculations with Gaussian basis functions. It contains a limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) optimization algorithm which uses a Cartesian coordinate system as input. L-BFGS is an optimization technique from the family of quasi-Newton methods that limits its memory usage while approximating the Broyden-Fletcher-Goldfarb-Shanno algorithm (BFGS). In general, the BFGS update of the inverse Hessian is: 3