INDO

The intermediate neglect of differential overlap (INDO) method was at one time used for organic systems. Today, it has been superseded by more accurate methods. INDO is still sometimes used as an initial guess for ah initio calculations. 

---

However, the CNDO method showed systematic weaknesses that were directly attributable to the approximations outlined above, so that it was superseded by the intermediate m lect of diatomic differential overlap (INDO) method, introduced by Pople, Beveridge, and Dobosh in 1967 [13]. The approximation outlined in Eq. (50) proved to be too severe and was replaced by individual values for the possible different types of interaction between two AOs. These individual values, often designated Cgg, Ggp, Gpp and in the literature, can be adjusted to give better agreement with experiment than was possible for CNDO. However, in INDO the two-center terms remain of the same type as those given in Eqs. (51) and (52) (again, there are many variations). This approximation leads to systematic weaknesses, for instance in treating interactions between lone pairs. 

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... 

Projeeled INDO the in itial guess at the MO eoeffieieu ts is obtained from an INIDO calculation. 

Con figuration Interaction (or electron correlation ) improves energy ealeii lalion s usin g CNDO, INDO,. MINLO/3,. MXDO, A.M 1, PM3, /INFiO/1, and /.INDO/S for th ese electron con figuration s... 

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. ... 

INDO/1 and /lNDO/.Sarc Dr. Michael /erner s INDO versions and used for m olecular syslein s w ith transition m etals,/INDO/1 is expected to give gcom dries of m oicculcs, and /INDO/S is param -clrixcd to give UV spectra. 

CXDO and INDO were developed by the Pople group at Carnegie Melon University. This group chose parameters based pri-... 

ZINDO/1 IS based on a modified version of the in termediate neglect of differen tial overlap (IXDO), which was developed by Michael Zerner of the Quantum Theory Project at the University of Florida. Zerner s original INDO/1 used the Slater orbital exponents with a distance dependence for the first row transition metals only. Ilow ever. in HyperChein constant orbital expon en ts are used for all the available elein en ts, as recommended by Anderson. Friwards, and Zerner. Inorg. Chem. 2H, 2728-2732.iyH6. 

ZINDO/S is an INDO method paramcteri/ed to reproduce LV visible spectroscopic transitions when used with the singly excited Cl method. It w as developed in the research group of Michael Zerner of the Quantum fheory Project at the University of Florida. 

The (juality of the vibrational fretjuen cies varies widely with the setTi i-eiTi pirical method that is used. Generally,. AMI, and l M3 are in eloser agi eem eii t with experiment than in elh ods based on C.NDO or INDO,... 

CNDO and INDO arc generally faster than the MIXDO/d, MXDO, AML and PM3 and require much less memory. Yon can apply them to molecules that are too large for MIXDO/d, MXDO, AMI, and PML... 

MIXDO/3 is the earliest of the Dewar methods. It provides more accurate geometries and heats of formation than CNDO or INDO. and has been used widely. The limitations of the INDO approximation, on which MI lhO/3 is based, frequently lead to problems of accuracy wdi cri dealing w i th m olecules con tain ing h eteroatorn s. 

A projected CNDO/INDO guess uses th e com puted coefficien ts from a minimum basis set CXDCi/[NDO calculation and then... 

III c dillci CTice between CNDO and INDO is best understood in relation to tli e plienonieriori of exch an ge, wli ich we briefly describe h ere. 

The one-eenter exchange integrals that INDO adds to the CNDO schcmccan be related to th e-Slater-Condon param eters h", O. and F used to describe atomic spectra. In particular, for a set of s, p,. p,.. t, atom ie orbitals, all the on e-ecn ter in tegrals are given as ... 

While INDO calciilaiioii s have more pariuiieiers an d are som ewh ill more complex that CXDO ciilciilatioim. they require csseii tiiilly no extra computation time and in most siluiilions they are superior to CNDO ciilculatioiis. 

Using the same nomenclature as for the INDO approximation, the elements of the MfNDOfS UHFFock matrix are described below. When < )j an d d tti iJ on different cen lers the off-diagonal elem en ts are... 

I hc coix-clt cti ()ri integral, as in CNIDO/INDO, is llicn equaled lo ihe correspon ding iwo-cleelron integral ... 

The basic idea of mixed model in MIXDO/3 is the same as that used for CNDO and INDO and corrects appears in the... 

HyperChem s im plem eti tatiori of/INDO/1 has been tested using param eters suggested by referen ces to work dorieby Zerueron first row transition metals. 

The basic equations of ZINDO/1 are the same as those m IXDO, except I orL i y. In stead of usiri g th e electron egativity in INDO, ZlNDO/l uses th e ion i,ration potential for computing Llj,... 

The mixed model used m ZINDO/1 is identical to that used in CXDO an d INDO if there is no d-orbital in volved in the t iian turn... 

---