zero differential overlap (ZDO) approximation
An approach to the systematic neglect of the small-in-value electron repulsion integrals which is used in a number of approximate self-consistent field molecular orbital schemes. It means that all the products of atomic orbitals χ µ χ ν are set to zero and the overlap integral S µ ​ ν = δ µ ​ ν (where δ µ ​ ν is the Kronecker delta). The ZDO approximation greatly simplifies the computation of wavefunctions by eliminating many of two-electron integrals. At the ZDO approximation all three- and four-centered integrals vanish.
PAC, 1999, 71, 1919. 'Glossary of terms used in theoretical organic chemistry' on page 1970 (