Avogadro Constants and Conversions

I am having a hard time finding the constants and conversions that Avogadro uses. For example, when I open an .fchk file from Gaussian in Avogadro, HOMO LUMO energies are listed in eV. In the output file from Gaussian they are listed in Hartree. Sometimes when I convert the values myself using 1 Hartree = 27.2114 eV I get a difference in the third decimal place. I am hoping to know the exact equation Avogadro is using for this conversion and others.

I wouldn’t be surprised if there’s a difference of ~0.001 eV. I’d have to check the whole path of reading the orbital energies, but you’re describing differences of ~0.00003-0.00004 Hartree. That’s seldom significant IMHO.