Spin Interactions in INDO

The advantages of INDO over CNDO involve situations where the spin state and other aspects of electron spin are particularly important. For example, in the diatomic molecule NH, the last two electrons go into a degenerate p-orbital centered solely on the Nitrogen. Two well-defined spectroscopic states, S and D, result. Since the p-orbital is strictly one-center, CNDO results in these two states having exactly the same energy. The INDO method correctly makes the triplet state lower in energy in association with the exchange interaction included in INDO. 

A second common example of the utility of INDO over CNDO is the methyl radical CH3. This planar molecule is a free radical with 

While INDO calculations have more parameters and are somewhat more complex that CNDO calculations, they require essentially no extra computation time and in most situations they are superior to CNDO calculations. 

Using the same nomenclature as for the INDO approximation, the elements of the MINDO/3 UHF Fock matrix are described below. When (]) j and (jty are on different centers the off-diagonal elements 

The two-center two-electron, one-center two-electron, two-center one-electron, one-center one-electron, and core-core repulsion integrals involved in the above equations are discussed below. 

---