Molecular orbital theory of the properties of inorganic and organometallic compounds. 6. Extended basis sets for second‐row transition metals

Abstract A series of efficient split‐valence basis sets for second‐row transitions metals, termed 3‐21G, has been constructed based on previously formulated minimal expansions of Huzinaga, and in a manner analogous to the previous development of 3‐21G basis sets for first‐row metals. The Huzinaga three Gaussian expansions for s‐ and p‐type orbitals of given n quantum number have been fit by least squares to new three Gaussian combinations in which the two sets of functions share the same Gaussian exponents. The original three Gaussian expansions for 1s, 3d, and 4d atomic orbitals have been employed as is. The valence description comprises 4d‐ 5s‐ and 5p‐type functions, each of which has been split into two and one Gaussian parts. 5p functions, while not populated in the ground state of the free atom, are believed to be important in the description of the bonding in molecules. The performance of the 3‐21G basis sets is examined with regard to the calculation of equilibrium geometries and normal‐mode vibrational frequencies for a variety of simple inorganic and organometallic compounds incorporating second‐row transition metals.