### The Exchange self-energy

The xxvxc runlevel calculates the matrix elements of the xc potential
(corresponding to the one used in the Ground state calculation),
and of the exchange self-energy. These matrix elements are used in the gowo runlevel to calculate the quasiparticle corrections.The exchange self-energy is defined as

which yields

The maximum vector in the reciprocal space used in the summation is EXXRLvcs while the bands summation can be started from
SxLowBnd . QPkrange (or alternatively QPErange ) selects the matrix elements (both exchange self-energy and xc potential) to
calculate. For the details on the integration in the BZ of the RL and on the treatment of the divergence of the Coulomb interaction refer to RIM.