Neglect of Diatomic Overlap

As we have seen, MINDO/3 was based on the INDO approximation, which could not represent lone-pair lone-pair interactions therefore, as expected, MINDO/3 had difficulty with systems which contained lone pairs. To rectify this, Dewar embarked on developing and parameterizing a wholly new method based on the NDDO approximation. This was completed by Dewar and Thiel only two years after MINDO/3 was published. They called the new method, which was published in 1977, modified neglect of diatomic overlap or MNDO.  

As with MINDO/3, the core-core repulsion term was made a function of the elearon-elearon repulsion integral  

The parameters to be used in MNDO were obtained using experimental data on 34 compounds. The parameters were optimized to reproduce observed heats of formation, dipole moments, ionization potentials, and molecular geometries. 

MNDO was a much more elegant method than MINDO/3. Instead of using diatomic parameters in the resonance integral and core-core repulsion, which had severely limited extending MlNDO/3 to new elements, MNDO used entirely monatomic parameters. 

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, containing both the MINDO/3 and MNDO mediods, which allowed various geometric operations, such as geometry optimization, constrained and unconstrained, with and without symmetry, transition state localization by use of a reaction co- 

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Highest occupied molecular orbital Intermediate neglect of differential overlap Linear combination of atomic orbitals Local density approximation Local spin density functional theory Lowest unoccupied molecular orbital Many-body perturbation theory Modified INDO version 3 Modified neglect of diatomic overlap Molecular orbital Moller-Plesset... 

The modihed neglect of diatomic overlap (MNDO) method has been found to give reasonable qualitative results for many organic systems. It has been incorporated into several popular semiempirical programs as well as the MNDO program. Today, it is still used, but the more accurate AMI and PM3 methods have surpassed it in popularity. 

MNDO (modified neglect of diatomic overlap) a semiempirical method model a simple way of describing something that is actually more complex than the model... 

The core-core repulsion of the Modified Neglect of Diatomic Overlap (MNDO) modeP has the form ... 

The systems discussed in this chapter give some examples using different theoretical models for the interpretation of, primarily, UPS valence band data, both for pristine and doped systems as well as for the initial stages of interface formation between metals and conjugated systems. Among the various methods used in the examples are the following semiempirical Hartree-Fock methods such as the Modified Neglect of Diatomic Overlap (MNDO) [31, 32) and Austin Model 1 (AMI) [33] the non-empirical Valence Effective Hamiltonian (VEH) pseudopotential method [3, 34J and ab initio Hartree-Fock techniques. 

Modified neglect of diatomic overlap (MNDO) calculations can support the structures assigned to certain of these fused tricyclic systems, such as 401, where confirmatory X-ray crystallographic data are lacking <1983JCM128>. 

A theoretical study of degenerate Boulton-Katritzky rearrangements concerning the anions of the 3-hydroxyimi-nomethyl-l,2,5-oxadiazole has been carried out by using semi-empirical modified neglect of diatomic overlap (MNDO) and ab initio Hartree-Fock procedures. Different transition structures and reactive pathways were obtained in the two cases. Semi-empirical treatment shows asymmetrical transition states and nonconcerted processes via symmetrical intermediates. By contrast, ab initio procedures describe concerted and synchronous processes involving symmetrically located transition states <1998JMT(452)67>. 

Various theoretical methods (self-consistent field molecular orbital (SCF-MO) modified neglect of diatomic overlap (MNDO), complete neglect of differential overlap (CNDO/2), intermediate neglect of differential overlap/screened approximation (INDO/S), and STO-3G ab initio) have been used to calculate the electron distribution, structural parameters, dipole moments, ionization potentials, and data relating to ultraviolet (UV), nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), photoelectron (PE), and microwave spectra of 1,3,4-oxadiazole and its derivatives <1984CHEC(6)427, 1996CHEC-II(4)268>. 

Modified Neglect of Diatomic Overlap -type Semiempirical Methods... 

This new model f6), called MNDO for Modified Neglect of Diatomic Overlap, was published oy Dewar and Thiel in 1977. With MNDO the average errors (5) for the same survey of C, H, N and O molecules decreased to 6.3 kcal/mol for AHf, 0.014 A for bond lengths and 0.48 eV for ionization potentials. Since MNDO used only atomic parameters, parameterization of MNDO to include additional elements was much easier than with MINDO/3, and, over the next eight years, parameters were optimized for 16 elements in addition to C, H, N and O. 

Values reported are averages from two levels of Hartree-Fock (HE) modified neglect of diatomic overlap (MNDO) theory in Ref 15. 

The performance of several semi-empirical (modified neglect of diatomic overlap (MNDO), AMI, PM3, and SAMI) and ab initio (Hartree-Fock (FIF) and MP2/6-31G ) methods for determining structural and electronic factors of a series of isothiazolo[5,4-b]pyridines was compared by Martinez-Merino et al. <1996T8947>. They found that most of the semi-empirical methods calculated reasonable molecular structures when compared to the actual X-ray structures (compounds 3-5) (see, for example. Table 1 for selected bond lengths of compound 3). Flowever, the dipole moments were not reproducible using these methods. 

A variety of more advanced, all-electron methods of this type Me available, and are generally referred to as semi-empirical calculations. The acronyms used to name the individual methods are descriptive of the manner in which atomic overlap calculations are performed. Among the more widely used semi-empirical methods are those of complete neglect of differential overlap (CNDO/2) (12), modified intermediate neglect of differential overlap (MINDO/3) (13), and modified neglect of diatomic overlap (MNDO) (14). 

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