The INDO Scheme

The next extension in semiempirical MO theory come with the introduction of the intermediate neglect of differential overlap (INDO) methods, by including all one-center-two-electron integrals in the Fock matrix. It was originally thought as a compromise between the lack of accuracy of CNDO methods and the (back then) large number of integrals required in other more complete schemes. It is therefore no longer a faithful implementation of the ZDO, but it is also not quite the next level of approximation, hence the intermediate in the theory’s name. We explore in the attached files the INDO methods of Pople and the extension of CNDO/BG to the INDO method, mentioning briefly other methods.

INDO.pdfDownload

INDOBG.pdfDownload

otherINDO.pdfDownload

Even though these methods showed their successes, it is very complicated to parameterise these methods in a generally applicable way that is furthermore also reliable. With the next level of approximation one gains transferability of parametrisations and significantly higher accuracy. This is the neglect of diatomic differential overlap approximation (NDDO).