Abstract — Calculation of the Coulomb potential in the molecular dynamics code ddcMD has been parallelized based on a hybrid MPI/OpenMP scheme. The explicit pair kernel of the particleparticle/particle-mesh algorithm is multi-threaded using OpenMP, while communication between multicore nodes is handled by MPI. We have designed a load balancing spanning forest (LBSF) partitioning algorithm, which combines: 1) finegrain dynamic load balancing; and 2) minimal memory-footprint data privatization via nucleation-growth allocation. This algorithm reduces the memory requirement for thread-private data from O(np) to O(n + p 1/3 n 2/3)—amounting to 75 % memory saving for p = 16 threads working on n = 8,192 particles, while maintaining the average thread-level load-imbalance less than 5%. Strong-scaling speedup for the kernel is 14.4 with 16-way threading on a four quad-core AMD Opteron node. In addition, our MPI/OpenMP code shows 2.58! and 2.16! speedups over the MPI-only implementation, respectively, for 0.84 and 1.68 million particles systems on 32,768 cores of BlueGene/P
