MINDO/3

There are three modihed intermediate neglect of differential overlap (MINDO) methods MINDO/1, MINDO/2, and MINDO/3. The MINDO/3 method is by far the most reliable of these. This method has yielded qualitative results for organic molecules. However its use today has been superseded by that of more accurate methods such as Austin model 1 (AMI) and parameterization method 3 (PM3). MINDO/3 is still sometimes used to obtain an initial guess for ah initio calculations. 

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A valuable review of th e MOP,AC program an d th e sem i-etn pirical methods MNDO. MINDO/3, AM I. and PM 3, Of particular use are th eoretical discussion s of these sem i-em pirical meth -ods and many tables validating the accuracy of the MOP.AC program and its associated Hamiltonians. 

Using Cl may not necessarily improve the calculation of ground slate cn crgics. Pararn eters for th e MINDO/3, MNDO,. AM I, and PM3 methods already iricltide the effects of Cl. Cl calculation s retjuire m ore corn pii ting time. 

The INDO meth od (In termediate N DO) corrects some of the worst problems with CNDO. Tor example, INDO exchange integrals between electrons on the same atom need not he eL tial, hut can depend on the orbitals involved. Though this introduces more parameters, additional compulation time is negligible. INDO and MINDO/11 (.Vlodilied INDO, version II) methods are different im piemen lalion s of the same approxim ation. ... 

MINDO/3, MNDO, and AM 1 wxrc developed by the Dervar group at the University of i exasat Austin. This group ehose many parameters, such as heats of formation and geometries of sample molecules, to reproduce experimental quantities. The Dewar methods yield results that are closer to experiment than the CN DO and IN DO methods. 

IXDCf is faster than MINDO/3, MNDO, AMI, and PM3 and, unlike C XDO, can deal with spin effects. It is a particularly appealing choice for UHF calculations on open-shell molecules. It is also available for mixed mode calculations (see the previous section ). IXDO shares the speed and storage advantages of C XDO and is also more accurate. Although it is preferred for numerical results, it loses some of the simplicity and inierpretability of C XDO. 

Che two-centre repulsion integrals 7ab in MINDO/3 are calculated using the following niaction ... 

T he core-core interaction between pairs of nuclei was also changed in MINDO/3 from the fiiriu used in CNDO/2. One way to correct the fundamental problems with CNDO/2 such as Ihe repulsion between two hydrogen atoms (or indeed any neutral molecules) at all di -l.inces is to change the core-core repulsion term from a simple Coulombic expression (/ ., ii = ZaZb/Rab) to ... 

III fact, while this correction gives the desired behaviour at relatively long separations, it doLS not account for the fact that as two nuclei approach each other the screening by the core electrons decreases. As the separation approaches zero the core-core repulsion iimild be described by Coulomb s law. In MINDO/3 this is achieved by making the cure-core interaction a function of the electron-electron repulsion integrals as follows ... 

Bingiiam R C, M J S Dewar and D H Lo 1975a. Ground States of Molecules. XXV. MINDO/3. An improved Version of the MINDO Semi-empirical SCFMO Method. Journal of the American Chemical Society 97 1285-1293. 

Bingham R C, M J S Dewar and D H Lo 1975b. Ground States of Molecules. XXVI. MINDO/3. 

The CNDO, INDO, NDDO, MNDO, and MINDO methods all are defined in terms of an orbital-level Foek matrix with elements... 

To illustrate the differences among the various approaches and to clarify how their parameters are obtained, let us consider two specific and popular choices- CNDO/2 and MINDO. 

Za,b = integrals are retained. In the INDO approach, the values of these single-atom integrals are determined by requiring the results of the calculation, performed at the Fock-like orbital level, to agree with results of ab initio Fock-level calculations. In the MINDO approach, experimental electronic spectra of the particular atom are used to... 

The semiempirical techniques available include EH, CNDO, INDO, MINDO/3, ZINDO, MNDO, AMI, and PM3. The ZINDO/S, MNDO/d, and PM3(TM) variations are also available. The semiempirical module seems to be rather robust in that it did well on some technically difficult test calculations. 

MINDO (modified intermediate neglect of differential overlap) a semiempirical method... 

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