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We present our recent code modernizations of the of the ab initio moleculardynamics program CPMD (www.cpmd.org) with a special focus on the ultra-softpseudopotential (USPP) code path. Following the internal instrumentation ofCPMD, all time critical routines have been revised to maximize thecomputational throughput and to minimize the communication overhead for optimalperformance. Throughout the program missing hybrid MPI+OpenMP parallelizationhas been added to optimize scaling. For communication intensive routines, asthe multiple distributed 3d FFTs of the electronic states and distributedmatrix-matrix multiplications related to the $\beta$-projectors of thepseudopotentials, this MPI+OpenMP parallelization now overlaps computation andcommunication. The necessary partitioning of the workload is optimized by anauto-tuning algorithm. In addition, the largest global MPI_Allreduce operationhas been replaced by highly tuned node-local parallelized operations using MPIshared-memory windows to avoid inter-node communication. A batched algorithmfor the multiple 3d FFTs improves the throughput of the MPI_Alltoallcommunication and, thus, the scalability of the implementation, both for USPPand for the frequently used norm-conserving pseudopotential code path. Theenhanced performance and scalability is demonstrated on a mid-sized benchmarksystem of 256 water molecules and further water systems of from 32 up to 2048molecules.

Integrating State of the Art Compute, Communication, and Autotuning  Strategies to Multiply the Performance of the Application Programm CPMD for  Ab Initio Molecular Dynamics Simulations