Guilin Sun
Ansys Employee

For extinction efficiency, please check its definition. Maybe it is simply normalized with geometry cross section.

It is uderstandable that you want to have the same result. However do you know the polarization the reference used? is it linear or circular or elliptical ?

Cross sections for absorption, scattering and extinction simulated by FDTD have been verified with theory. Therefore please check carefully the settings and the reference. I have a post which lists a dozen of issues to be checked: 

Ansys Insight: Why my simulation result is different from published paper or experiment?