First, we measure the time required to perform a single Davidson iteration as a function of the number of CPU cores for the two largest wave functions (N det = 25 × 10 6 and 100 × 10 6 ). e timings are reported in Table while the parallel speedup curve is represented in Fig. . e parallel e ciency increases together with N det , as shown in Fig. . For the largest wave function, a parallel e ciency of 66% is obtained on 192 nodes (i.e. 9216 cores). We note that the speedup reaches a plateau at 3 072 cores (64 nodes) for N det = 25 × 10 6 . For this wave function, there are 625 tasks computing each 40 000 rows of W. When the number of nodes reaches 64, the number of tasks is too small for the load to be balanced between the nodes, and the computational time is limited by the time taken to compute the longest task. e same situation arises for N det = 100 × 10 6 with 9 408 cores (192 nodes), with 2 500 tasks to compute.