HFALPHA
HFALPHA = [real]
Default: HFALPHA = -1
Description: HFALPHA specifies how the Coulomb kernel is approximated at G=0 when the Fock energy and the exchange potential are evaluated.
For details we refer to HFRCUT. If the method of Massida, Posternak and Baldereschi is used [S. Massida, M. Posternak, and A. Baldereschi, Phys. Rev. B 48, 5058 (1993)], HFALPHA specifies the decay constant in the error-function-like charge distribution that is used to calculate the difference between the isolated probe charge and the periodically repeated probe charge in the homogenous background. The default for HFALPHA is 6/sqrt(ENMAX)/(2 pi) (in atomic units).