sanya
sanya@photonics.ru
Just remove diffuse functions on inner atoms and leave them only on peripheral atoms. You'll have something like 6-31+G* on peripheral hydrogens (* in case of hydrogens means polarization p functions) and 6-31G* on carbons (here, * means polarization d functions). Diffuse functions on inner atoms cause linear dependence. Can I look at your molecule (*.inp or *.xyz file) to tell you more definitely which atoms should have diffuse functions?