u can get the electron affinity from quantum mechanical descriptors try reading a theoretical paper and use koopmans theorm . plus if u r well versed with gaussian 03 . then get the molecule optimised and from the results of the output u will get ur electron affinity.

work function of Iron pyrite is 5.40 eV you will search the article

http://avs.scitation.org/doi/pdf/10.1116/1.1379320

and electron affinity of FeS2 is 3..09 .

http://pubs.rsc.org/en/content/articlehtml/2002/cp/b207188f

http://astro1.panet.utoledo.edu/~relling2/PDF/pubs/nanocrystalline_FeS2_as_back_contact_to_CdTe_(2014)_pvsc.pdf

Thank you punit