Neglect of differential diatomic overlap

The first practical NDDO method was introduced by Dewar and Thiel in 1977.90 Called modified neglect of diatomic overlap (MNDO), the model was again parameterized on experimental molecular geometries, heats of formation, dipole moments, and ionization potentials. 

The Fock matrix in MNDO has the form of Eq. [13]. The orbital exponents and the core integral were again treated as empirical parameters to be determined in the fitting procedure. As with MINDO/3, the core-core repulsion term was made a function of the electron-electron repulsion integral  

The empirical determination of the resonance integral (J and the core-core repulsion returned to a procedure that was orbital or atom based, rather than atom-pair based, allowing an easier extension to more atoms of the periodic system. 

Over the next decade MNDO parameters were derived for lithium, beryllium, boron,fluorine, aluminum, silicon, phosphorus, sulfur, chlorine, zinc, germanium,bromine, iodine, tin, mercury, and lead.  

In 1983 the first MOPAC program was written and contained both the MlNDO/3 and MNDO models. This program allowed geometry optimization, transition state location by use of a reaction coordinate, gradient minimizations, and vibrational frequency calculations. MNDO has been applied with success to the prediction of polarizabilities, hyperpolarizabilities, ESCA, nuclear quadrupole resonance, and numerous other properties.  

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In order to overcome these weaknesses, Pople and co-workers reverted to a more complete approach that they first proposed in 1965 [14], neglect of diatomic differential overlap (NDDO). In NDDO, all four-center integrals (pv are considered in which p and v are on one center, as are 2 and cr (but not necessarily on the same one as and v). Furthermore, integrals for which the two atomic centers are diEFer-ent are treated in an analogous way to the one-center integrals in INDO, resulting... 

I lie next level of approximation is the neglect of diatomic differential overlap model (NDDO [Pople et al. 1965]) this theory only neglects differential overlap between atomic orbitals on... 

Neglect of diatomic differential overlap Parametrisation 3 of MNDO... 

The NDDO (Neglect of Diatomic Differential Overlap) approximation is the basis for the MNDO, AMI, and PM3 methods. In addition to the integralsused in the INDO methods, they have an additional class of electron repulsion integrals. This class includes the overlap density between two orbitals centered on the same atom interacting with the overlap density between two orbitals also centered on a single (but possibly different) atom. This is a significant step toward calculatin g th e effects of electron -electron in teraction s on different atoms. 

PM3, developed by James J.P. Stewart, is a reparameterization of AMI, which is based on the neglect of diatomic differential overlap (NDDO) approximation. NDDO retains all one-center differential overlap terms when Coulomb and exchange integrals are computed. PM3 differs from AMI only in the values of the parameters. The parameters for PM3 were derived by comparing a much larger number and wider variety of experimental versus computed molecular properties. Typically, non-bonded interactions are less repulsive in PM3 than in AMI. PM3 is primarily used for organic molecules, but is also parameterized for many main group elements. 

PM3 is a reparameterization of AMI, which is based on the neglect of diatomic differential overlap (NDDO) approximation. NDDO... 

The second basic approximation is the neglect of diatomic differential overlap... 

The neglect of diatomic differential overlap approximation used in the semi-empirical methods reduces these formulae to much simpler formulae that can be computed quite rapidly,... 

In the Neglect of Diatomic Differential Overlap (NDDO) approximation there are no further approximations than those mentioned above. Using p and n to denote either an s-or p-type (pj, p or p ) orbital, the NDDO approximation is defined by the following equations. 

Neglect of diatomic differential overlap (NDDO) technique, 16 737 Negligible failure, 26 982 Negotiations, in technology transfer, 24 363-366... 

This is referred to as the Neglect of Diatomic Differential Overlap or NDDO approximation. It reduces the number of electron-electron interaction terms from 0(N ) in the Roothaan-Hall equations to 0(N ), where N is the total number of basis functions. 

NDDO Approximation. Neglect of Diatomic Differential Overlap approximation. The approximation underlying all present generation Semi-Empirical Models. It says that two Atomic Orbitals on... 

III. The All-Valence Electrons, Neglect of Diatomic Differential Overlap... 

The partial neglect of differential overlap (PNDO) method, originally referred to as the partial neglect of diatomic differential overlap (PNDDO) introduced by Dewar and Klopman 28>, is to date the only method to adopt... 

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