Modified INDO MINDO

Several versions of modified INDO (MINDO) that employ such a parameterization have been proposed. These include MINDO/1, MINDO/2, MINDO/2, and MINDO/3, only the last of which resulted in a quantum chemical program that was widely used. MINDO/3151 is parameterized for H, B, C, N, O, F, Si, P, S, and Cl, although certain combinations of these atoms are not parameterized. The MINDO/3 method is no longer heavily used because the parameterized NDDO methods are generally more accurate. 

In the late 1960s and early 1970s, Dewar and co-workers developed the modified INDO (MINDO) methods. In 1976, the modified neglect of diatomic overlap (MNDO) method " was introduced. Further refinements were made to MNDO and improved parametrizations, AMI Austin model 7) PM3 parametric method and PM5 parametric method 5), ... 

An alternative strategy was to develop methods wherein the two-electron integrals are parameterized to reproduce experimental heats of formation. As such, these are semi-empirical molecular orbital methods—they make use of experimental data. Beginning first with modified INDO (MINDO/1, MlNDO/2, and MINDO/3, early methods that are now little used), the methodological development moved on to modified neglect of diatomic differential overlap (MNDO). A second MNDO parameterization was created by Dewar and termed Austin method 1 (AMI), and finally, an "optimized" parametrization termed PM3 (for MNDO, parametric method 3) was formulated. These methods include very efficient and fairly accurate geometry optimization. The results they produce are in many respects comparable to low-level ab initio calculations (such as HF and STO-3G), but the calculations are much less expensive. 

The INDO method (Intermediate NDO) corrects some of the worst problems with CNDO. For example, INDO exchange integrals between electrons on the same atom need not be equal, but can depend on the orbitals involved. Though this introduces more parameters, additional computation time is negligible. INDO and MINDO/3 (Modified INDO, version 3) methods are different implementations of the same approximation. 

With the intermediate NDO method ZDO is not assumed between a.o. s on the same atom in one-centre electron repulsion integrals. Various other schemes based on different ZDO assumptions together with different schemes of semi-empirical parametrization have been developed. These have become known by their acronyms such as CNDO/1, CNDO/2, INDO, MINDO/3 (m - modified), NDDO (d - diatomic), MNDO etc.. 

The first general parameterization to be reported by Dewar and co-workers was a third-generation modified INDO model (MINDO/3 Bingham, Dewar, and Lo, 1975). Some of the specific modifications to the INDO framework included the use of different t exponents in s and p type STOs on the same atom, the definition of pair parameters /Iab between two atoms A and B that were not averages of atomic parameters (actually, four such parameters... 

A modified INDO model that is not entirely obsolete is the symmetric orthogonal-ized INDO (SINDOl) model of Jug and co-workers, first described in 1980 (Nanda and Jug 1980). The various conventions employed by SINDOl represent slightly different modifications to INDO theory than those adopted in the MINDO/3 model, but the more fundamental difference is the inclusion of d functions for atoms of the second row in the periodic table. Inclusion of such functions in the atomic valence basis set proves critical for handling hyper-valent molecules containing these atoms, and thus SINDO1 performs considerably better for phosphorus-containing compounds, for instance, than do otlier semiempirical models that lack d functions (Jug and Schulz 1988). 

The first (1967) of the Dewar-type methods was PNDDO [35], partial NDDO), but because further development of the NDDO approach turned out to be unexpectedly formidable [33], Dewar s group temporarily turned to INDO, creating MINDO/1 [36] (modified INDO, version 1). The third version of this method, MINDO/3, was said [33] [to have] so far survived every test without serious failure , and it became the first widely-used Dewar-type method. Keeping their promise to return to NDDO the group soon came up with MNDO (modified NDDO). MINDO/3 was made essentially obsolete by MNDO, except perhaps for the study of carbocations (Clark has summarized the strengths and weaknesses of MINDO/3, and the early work on MNDO [37]). MNDO (and MNDOC and MNDO/d) and its descendants, the very popular AMI and PM3, are discussed below. Briefly mentioned are a modification of AMI called SAMI and an... 

Modified INDO procedure of Dewar, also MINDO/2, MINDO/3 Molecular Orbital... 

In 1975 Dewar and his co-workers introduced the MINDO/3 model, a third parameterization of a modified INDO model. This model was developed to reproduce such diverse experimental properties as molecular geometries, heats of formation, dipole moments, and ionization potentials. This systematic study of parameters within this model cost millions of dollars, but in doing so was better able to test the inherent accuracy of the model as opposed to inaccuracies introduced through poor parameters. 

The first useful Dewar-type theory was the MINDO/3 (third version of the modified INDO) method, published in 1975. For a sample of compounds containing no elements other than C, H, O, and N, the average absolute errors in MINDO/3 calculated properties are 11 kcal/mol in heats of formation, 0.022 A in bond lengths, 5.6° in bond angles, 0.49 D in dipole moments, and 0.7 eV in ionization energies. The errors in A.H°f 29S are larger than Dewar was aiming for. 

EHT, extended Huckel theory CNDO, complete neglect of differential overlap INDO, intermediate neglect of differential overlap NNDO, neglect of diatomic differential overlap SCF, self-consistent field MINDO, modified INDO ab initio, without the use of independently derived parameters. For an independent assessment of the different molecular orbital methods applied to carbocations, see Ref. 3. 

---