Low-lying States of Tl2 and Nh2 with EOM-CC and FSCC Methods

Multireference character in the electronic structure of Tl2 and Nh2 is significant and spin?orbit coupling plays an important role in their properties. Single-reference EOM-CCSD and multi-reference IHFSCCSD methods are employed to investigate their low-lying states. Excitation energies with these two methods agree well with each other, while bond lengths with EOM-CCSD are usually too long. Our results on Tl2 agree well with previous MRCI results except that the present bond lengths are generally about 0.1?0.2 ? shorter. As for Nh2, the lowest two states are weakly bounded and the fourth excited state has a stronger chemical bond.