Calculation of X-ray Refractive Index:

where

l is the x-ray wavelength
r_e = 2.817´10^-5 Å, is the classical electron radius
n_i = N/V Å^-3, is the number of i^th atom per unit volume
N is the number of atom in the unit cell of volume V
f_i = f_i' + j f_i", is the scattering factor of the i^th atom at l (or E)
E = 12.39/l; E is in keV when l in Å

Conversion Relations (one to one):