Parallel Implementation

In an ab-initio approach, the system is driven by electrostatic interactions between the nuclei and electrons. Calculating the electrostatic energy involves computing several terms: (1) quantum mechanical kinetic energy of non-interacting electrons, (2) Coulomb interaction between electrons or the Hartree energy, (3) correction of the Hartree energy to account for the quantum nature of the electrons or the exchange-correlation energy, and (4) interaction of electrons with atoms in the system or the external energy. Hence, CPAIMD computations involve a large number of phases (Figure 1) with high interprocessor communication. These phases are discretized into a large number of virtual processors which generate a lot of communication, but ensures efficient interleaving of work. The various phases are:

Figure 1: Flow of control in OPENATOM
Image OpenAtomDiagram

For a detailed description of this algorithm please refer to [6]. We will now proceed to understand the communication involved in these phases through a description of the various chare arrays involved and dependencies among them.

Nikhil Jain 2015-08-14