In the B3LYP-based simulations, the use of two task groups extends the scaling limit of a BO-MD by a factor of two (Fig. ). This makes it possible to use up to 1,920 cores with an efficiency of 85% and a time per time-step of about 5.3 seconds only. Further addition of task groups, though, causes a decline in performance, typical of a system with a small number of orbitals where the additional communication between groups in the QM part outweighs the gain in performance due to task distribution. Similarly, for the B3LYP-based CP-MD run, the application of task grouping does not improve the scaling limit, which is the same as the one observed for BLYP. Upon investigation, we found that the reasons for the decline in performance are of the same nature as the stalling of the scaling performance of BLYP-based CP-MD outlined above (i.e. the serial integrator and the communication overhead).