# Exact Exchange

Gamma Point Parallel Implementation. Please, note that the new implementation will be available in the forthcoming CPMD release (available from version 3.17.1).

## New Parallel Implementation

Including the corrections reported in:

F. Gygi and A. Baldereschi Phys Rev Lett 62, 2160 (1989)

P. Broqvist, A. Alkauskas, and A. Pasquarello Phys. Rev. B 80, 085114 (2009)

We have implemented a new taskgroup Strategy (** V. Weber, T. Laino, A. Curioni**, IPDPS 2014 - available here with the permission of the authors), in which we distribute at the same time States and Orbital Couples.

The cost of the Exact Exchange scales as N^{2 }M logM, where N is the number of states and M the PW mesh.

In the new parallel scheme we exploit:

- that each group computes a subset of the orbital (non redundant) pairs

- cyclic distribution of the pairs (scalapack like)

- that the X-energy and the X-contribution to the electronic gradient are summed/redistributed at the end of the computation (inter groups communication)

- possible thresolding via orbital localization and overlap densities estimation

## Li/Air Batteries ( approximately 700 atoms ) - PBE0 (SCF performance)

## Li/Air Batteries ( approximately 1500 atoms ) - PBE0 (MD performance)

Strong scalability run (up to 96 BG/Q racks or 6 Millions threads).

Numbers on markers depict run time per MD step