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HFALPHA = [real]
|Default: HFALPHA||= 6/sqrt(ENMAX)/(2π)||if HFRCUT is 0|
HFALPHA sets the decay constant in the error-function-like charge distribution for the method of Massida, Posternak, and Baldereschi. The error-function-like charge distribution is used to calculate the difference between the isolated probe charge and the periodically repeated probe charge in a homogenous background. The default for HFALPHA is 6/sqrt(ENMAX)/(2π) in atomic units. This usually yields robust and accurate results in the range of meV compared to the Ewald summation used for a regular k-mesh. For more details, see HFRCUT=0.