## zero differential overlap approximation (ZDO approximation)

https://doi.org/10.1351/goldbook.ZT07132
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 $$\unicode[Times]{x3C7} _{\unicode[Times]{x3BC} }\ \unicode[Times]{x3C7} _{\unicode[Times]{x3BD} }$$ are set to zero and the overlap integral $$\text{S}_{\unicode[Times]{x3BC} \unicode[Times]{x3BD} } = \unicode[Times]{x3B4} _{\unicode[Times]{x3BC} \unicode[Times]{x3BD} }$$ (where $$\unicode[Times]{x3B4}_{\unicode[Times]{x3BC}\unicode[Times]{x3BD} }$$ 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.
Source:
PAC, 1999, 71, 1919. 'Glossary of terms used in theoretical organic chemistry' on page 1970 (https://doi.org/10.1351/pac199971101919)