(Experimental) This variable selects the method used for the treatment of the
singularity of the Coulomb potential in Hatree-Fock and hybrid-functional DFT calculations.
This shoulbe be only applied for periodic systems and is only
used for FFT kernels of the Poisson solvers.
Options:
none:
The singularity is replaced by zero.
general:
The general treatment of the singularity, as described in Carrier et al, PRB 75 205126 (2007).
This is the default option
fcc:
The treatment of the singulariy as described in Gygi and Baldereschi, PRB 34, 4405 (1986).
This is formally valid for cubic systems only.
spherical_bz:
The divergence in q=0 is treated analytically assuming a spherical Brillouin zone