calculate X-ray absorption coefficient

[toqduj]

There are some hints in the documentation on how to calculate the X-ray absorption coefficient (from f2?? or by using the imaginary component of the sld?) using periodic table, but I can't figure it out... how would this be calculated (in 1/m for example) from the formula, density and wavelength, and can there be a convenience method for this?

I tried applying the relations in the table from http://gisaxs.com/index.php/Absorption_length to the imaginary part output by pt.xray_sld(material, energy=energy_keV, density=self.density), but that doesn't seem to be right.