MNDO/3 method

The one-center two-electron integrals in the MNDO method are derived from experimental data on isolated atoms. Most were obtained from Oleari s work L. Oleari, L. DiSipio, and G. DeMich-ells. Mol. Phys., 10, 97( 1977)1, but a few were obtained by IDewar using fits to molecular properties. 

C oniparing ihc corc-core repulsion ol lhe above two ec nations with those in the MNDO method, it can be seen that the only dil -ference is in the last term. The extra terms in the AMI core-core repulsion deline spherical Ciaiissian Tun ctioii s — the a. h, and c are adjustable parameters. AMI has between two and I onr Gaussian full ctiori s per atom, ... 

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. 

Apractical introduction to molecular mechanics and semi-empirical quantum mechanics calculations, with extensive examples from the MMP2 (not in HyperChem), MINDO/3, and MNDO methods. One of the more accessible books for new computational chemists. 

Results of a recent literature study indicate that frequencies computed using semi-empirical PM3, AMI, and MNDO methods compare well to values obtained at iht ab initio level using medium size basis sets. Of these three methods, PM3 showed the closest correspondence to experimental values, which is generally about 10 percent too high in value from stretches (Seeger, D.M. Korze-niewski, C. Kowalchyk, W., J. Phys.Chem. 95 68-71, 1991). 

The MNDO method has 22 unique two-center two-electron integrals for each pair of heavy (non-hydrogen) atoms in their local atomic frame. They are ... 

In the MNDO method, the one-center one-electron integral, is given by ... 

In the MNDO method the resonance integral, is proportional to the overlap integral,... 

Fig. 11. Abundance mass spectra of differently charged hot CgoLL clusters evaporating atoms calculated with a Monte-Carlo simulation (the Li and Cgg isotope distributions are included). Energies required to remove Li atoms were calculated using the MNDO method. The peaks at x = 12 and at x = 6 + n (where n is the cluster charge) observed in experiment (Fig. 9) are well reproduced.

Heats of formation, molecular geometries, ionization potentials and dipole moments are calculated by the MNDO method for a large number of molecules. The MNDO results are compared with the corresponding MINDO/3 results on a statistical basis. For the properties investigated, the mean absolute errors in MNDO are uniformly smaller than those in MINDO/3 by a factor of about 2. Major improvements of MNDO over MINDO/3 are found for the heats of formation of unsaturated systems and molecules with NN bonds, for bond angles, for higher ionization potentials, and for dipole moments of compounds with heteroatoms. 

Arguing that the MNDO method is more suitable than the AMI method for predicting the heats of formation of five-membered nitrogenated aromatic rings, Garcia and Vilarrasa (88H1803) calculated that 4-fluoroimidazole 14a (R = F, = H) is 2.5 kJ mol more stable than its tautomer 14b,... 

FMO calculations using the MNDO method and electron-density calculations were performed to establish which calculations are in agreement with the experimentally observed regioselectivity of the SnH amination of some nitronaphthyridines (see Section III,B). 

The enthalpies ofall the annular tautomers of l,3,4-oxadiazin-5-ones 117 and -2-ones 118 were calculated using the MNDO method (88CB887). The results clearly indicated that in both cases the hydrazone-type tautomers 117a and 118a are the most stable, while the formation of the tautomer 118c is the least probable. 

Formal charge densities have been calculated for 3//-azepine and for the 3/7-azcpinium cation using MNDO methods,70 and 7>charge densities for 2//-azepin-2-one, 3//-azepin-3-one, and 4//-azepin-4-one have been calculated using the semiempirical method of Pariser. Parr and Pople.97... 

More recently Gorelik s group determined the structure of 1-phenylsulfonyl-2-pyrazoline-3-diazonium tetrafluoroborate by X-ray crystallography (Gorelik et al., 1989) and calculated (Glukhovtsev et al. 1990) the heats of the dediazoniation reaction of seven cyclic five-membered diazonium ions (including 2.13, R=H) relative to that of the benzenediazonium ion by the MNDO method (see Sec. 8.4). 

The MNDO method [17] coupled with the finite perturbation (FP) technique [18], as implemented in the MOPAC5 [19] program has been used throughout this work. 

Despite these modifications there remain a number of well-documented problems with the AM1/PM3 core-repulsion function [37] which has resulted in further refinements. For example, Jorgensen and co-workers have developed the PDDG (pair-wise distance directed Gaussian) PM3 and MNDO methods which display improved accuracy over standard NDDO parameterisations [38], However, for methods which include d-orbitals (e.g. MNDO/d [23,24], AMl/d [25] and AMI [39,40]) it has been found that to obtain the correct balance between attractive and repulsive Coulomb interactions requires an additional adjustable parameter p (previously evaluated using the one-centre two-electron integral Gss, Eq. 5-7), which is used in the evaluation of the two-centre two-electron integrals (Eq. 5-8). 

Addition of ammonia as a model nucleophile to nitrile oxides was studied by a semiempirical MNDO method, for fulminic acid and acetonitrile oxide (121). The reaction is exothermic and proceeds in two steps. The first (and rate-determining) step is the formation of a zwitterionic structure as intermediate. The second step, which involves transfer of a proton, is very fast and leads to the formation of Z-amidoximes in accordance with experimental data. Similar results were... 

Demiralp E, Cagin T, Goddard WA(1999) Morse stretch potential charge equilibrium force field for ceramics Application to the quartz-stishovite phase transition and to silica glass. Phys Rev l tt 82 1708-1711 Dewar MJS (1977) Ground states of molecules. The MNDO method. Approximations and parameters. J Am Chem Soc 99 4899-4907... 

The MNDO method has been employed " to study the acid-catalysed rearrangement of propylene 1,2-glycol. Propanaldehyde was found to be the major product with a small amount of acetone also being produced. The solid-state pinacol rearrangement of l,l,2-triphenylethane-l,2-diol has been performed over various solid... 

The various tautomers and rotamers of alloxan have been examined in detail by the MNDO method and it is predicted that the keto form is most important in the gas phase, although in solution the monohydroxy forms are also thought to contribute. A mass spectral study has been used to investigate the enol-keto tautomeric equilibria of a series of substituted salicylaldehyde and 2-hydroxynaphthaldehyde Schiff bases. In neutral, ethanolic solutions, the cis- and trans-tm forms of 4,5-dimethyl-2-(2 -hydroxyphenyl)imidazoles (393) and (394) have been found to exist in equilibrium in the ground state. However, in neutral aqueous solutions, the trans-eao and keto forms (394) and (395) were the only species detected. Deuterium isotope effects on... 

Makino, M., Kamiya, M., and Matsushita, H. Photodegradation mechanism of 2,3,7,8-tetrachlorodibenzo-jo-dioxin as studied by thePM3-MNDO method, Chemosphere, 24(3) 291-307, 1992. 

All computations were carried out using the MNDO method (12) and published parameters (15). For the cyclic structures, transits of a perpendicular main-group moiety across the various rings generate structures (n=l-6) as shown below. 

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