Geometry optimization of organometallic complexes: A study of basis sets

Total geometry optimizations are reported for Cr(CO)6, HMn(CO)5, Fe(CO)5, Ni(CO)4, Cr(C6H6)2, Fe(C5H5)2, Ni(C4H4)2, Cr(NO)4, (C5H5)Mn(CO)3, and (C6H6)Cr(CO)3. A variety of basis sets were examined, and, based on the results, a relatively compact and accurate basis set is proposed. The differences between the calculated and experimental metal-carbonyl, metal-benzene, and metal-nitrosyl bond distances average 0.03, 0.08, and 0.07 Å, respectively. Calculated metal-cyclopentadienyl bond lengths were found to be an average of 0.15 Å longer than experimental bond lengths. Addition of electron correlation at the perfect pairing GVB level reduced the average difference in the metal-cyclopentadienyl bond length to 0.08 Å.