The behavior of the BLYP-based simulations with a small QM system is similar to the one of butanol (see Fig. ). BO-MD scales up to 960 cores with a single time step taking 6.53 seconds. However, there is a drastic decline in the CP-MD performance. For this special case, it is not possible to use more than 480 cores with reasonable efficiency. The reason for this lies in the large size of the MM subsystem and the associated large number of constraints. This, together with the serial velocity-and coordinate-updates in the CPMD integrator, stalls the scaling (see Fig. ). The picture is rather different when the small QM subsystem is treated at the B3LYP level. These benchmarks have been run on the JUWELS supercomputer, due to the signifi- cant computational resources required. The use of task groups makes it possible to push the scaling limit up to 13,440 cores by using 14 groups, thus reducing the wall time spent per each BO-MD time step to around 13.76 seconds (Fig. ). In line with the scaling behaviour observed for the other systems, the use of task groups is less beneficial for CP-MD. Even so, it is possible to use two task groups, thus pushing the scaling limit to 1,920 cores. The stalling of the scaling can again be attributed to the inferior scaling of the orthogonalizer used to enforce the orthonormality constraint in CP dynamics at every time step, as well as the number of orbitals (49) where, with its large prime factors, it is not trivial to achieve a reasonable load distribution.