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CSHIFT: complex shift in Kramers-Kronig transformation

CSHIFT= [real]

Default: CSHIFT=0.1

The implemented Kramers-Kronig transformation uses a small complex shift $ \eta=$ CSHIFT in Eq. (6.76). The default for this shift is 0.1, which is perfectly acceptable for most calculations and causes a slight smoothening of the real part of the dielectric function. If the gap is very small (i.e. approaching two times CSHIFT), slight inaccuracies in the static dielectric constant are possible, which can be remedied by decreasing CSHIFT. If CSHIFT is further decreased, it is strongly recommended to increase the parameter NEDOS to values around 2000 (see Sec. 6.37).

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