Hardware Requirements

CPMD runs on a large variety of different computer architectures and is optimized to run on either (super)scalar or vector CPUs. The requirements on the capability of the hardware depend very much on the individual problem. While small test jobs can be easily run on a small single processor laptop computer and execute quite fast, most serious projects require a substantial amount of compute power to be completed within a reasonable amount of time (if at all). In that respect it is important to note, that the computational demands do not scale linearly with the system size. For small to medium size systems the time spent to compute the fast Fourier transforms dominates while for larger systems linear algebra operations become more time consuming as they have a less favorable scaling behavior with system size. Similarly the memory requirements increase significantly with the system size.

To cope with the computational demands of larger systems, CPMD has to be run in parallel. To be able to deal with the memory requirements CPMD employs a distributed memory parallelization scheme (i.e. using more nodes should reduce the memory consumption per node). As a consequence the requirements to network performance are very high. A gigabit ethernet interconnect will scale only to a small number of nodes. For good scaling a network technology like InfiniBand, Myrinet, Quadrics, Dolphin/SCI or a like is needed, and the best scaling is achieved on special parallel hardware with lightweight kernels like IBM BlueGene class or Cray XT$x$ type machines.