computational chemistry Computational chemistry is a branch of chemistry that uses computer simulation to assist in solving chemical problems. It uses methods of theoretical chemistry, incorporated into computer programs, to calculate the structures and properties of m ...

, NDDO (neglect of diatomic differential overlap) is a formalism that was first introduced by

John Pople Sir John Anthony Pople (31 October 1925 – 15 March 2004) was a British theoretical chemist who was awarded the Nobel Prize in Chemistry with Walter Kohn in 1998 for his development of computational methods in quantum chemistry. Early ...

and it is now the basis of most successful semiempirical methods. While

INDO Indo may refer to: * Indo-, a prefix indicating India or the Indian Subcontinent * Indonesia, a country in Asia ** INDO LINES, callsign of Indonesian Airlines ** Indo people, people of mixed European and Indonesian ancestry ** Indo cuisine, fusion ...

added all one-centre two electron integrals to the

CNDO/2 CNDO is the abbreviation for Complete Neglect of Differential Overlap, one of the first semi empirical methods in quantum chemistry. It uses two approximations: *core approximation - only the outer valence electrons are explicitly included. * zer ...

formalism, NDDO adds all two centre integrals for repulsion between a charge distribution on one centre and a charge distribution on another centre.J. Pople and D. Beveridge, ''Approximate Molecular Orbital Theory'', McGraw-Hill, 1970 Otherwise the

zero-differential overlap Zero differential overlap is an approximation in computational molecular orbital theory that is the central technique of semi-empirical methods in quantum chemistry. When computers were first used to calculate bonding in molecules, it was only pos ...

approximation is used. A common software program is MOPAC (Molecular Orbital PACkage). In the Neglect of Diatomic Differential Overlap (NDDO) method the overlap matrix S is replaced by the unit matrix. This allows one to replace the Hartree–Fock secular equation , H–ES, = 0 with a simpler equation , H–E, =0. The two-electron integrals from the NDDO approximation can either be one-, two-, three- or four-centered. The one-and two-centered integrals are evaluated approximately or parameterized based on the experimental data while the three- and four-centered integrals vanish. Usually, only the valence electrons are treated quantum mechanically while the role of core electrons is to reduce the nuclear charge. Semiempirical calculations are usually carried out in a minimal basis set.

References

Semiempirical quantum chemistry methods {{quantum-chemistry-stub

See also

References