Hence, we have 3 layers of parallelism in P : OpenMP, MPI and ZeroMQ. is allows for an elastic management of resources: a running calculation taking too much time can be dynamically accelerated by plugging in more computing resources, by submi ing more jobs in the queue or possibly in the cloud, i.e. outside of the HPC facility. is scheme has the advantage that it is not necessary to wait for all the nodes to be free to start a calculation, and hence minimizes the waiting time in the batch queue. It also gives the possibility to use altogether di erent helper programs. For instance, one could use a speci c GPU-accelerated helper program on a GPU node while CPU-only helpers run on the CPU-only partition of the cluster. It is also possible to write a helper program that helps only one PT2/selection step and then exit, allowing to gather resources a er the PT2/selection has started, and freeing them for the following diagonalization step.