Symmetrically orthogonalized INDO

Symmetrically Orthogonalized INDO (Method) Minimum Basis Set of Slater-type Orbitals, each Represented by 3 Gaussian Orbitals... 

CNDO/S, CNDO/FK, CNDO/BW, INDO/1, INDO/2, INDO/S and SINDOl. These methods are rarely used in modem computational chemistry, mainly because the modified methods described below usually perform better. Exceptions are INDO based methods, such as SlNDOl and INDO/S. SINDO Symmetric orthogonalized INDO) employes the INDO approximations described above, but not the ZDO approximation for the overlap matrix. The INDO/S method (INDO parameterized for Spectmscopy) is especially designed for calculating electronic spectra of large molecules or systems involving heavy atoms. 

One year after INDO/S, the method SINDOl (symmetrically orthogonalized INDO/1) by Nanda and Jug [58] was introduced. Originally developed for organic compounds of first-row elements, it was later extended to elements of the second and third row [59,60]. This method has several distinct features. The most important is that the orthogonalization transformation [Eq. (14)] is taken into account by a Taylor expansion. The matrix S-1/2 is approximated as... 

Semiempirical SCF calculations were done using the approximations NDDO (neglect of diatomic differential overlap) [18], MNDO (modified neglect of diatomic overlap) [19], INDO (intermediate neglect of differential overlap) [20], SINDO (symmetrically orthogonalized INDO [21]) [22], and CNDO (complete neglect of differential overlap) [20, 23]. Another type of approximation [24] to the ab initio method was also applied to OF2 [16]. 

Orbital energies from other ab initio calculations pertain to assumed bond lengths [9] or to the experimental geometry [13, 14]. Orbital energies were also calculated semiempirically by the extended Hiickel method [11], by CNDO [15], INDO [15, 16], MNDO [17], and SINDO [18] (symmetrically orthogonalized INDO, see [19]). 

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). 

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