MNDOC

A variation on MNDO is MNDO/d. This is an equivalent formulation including d orbitals. This improves predicted geometry of hypervalent molecules. This method is sometimes used for modeling transition metal systems, but its accuracy is highly dependent on the individual system being studied. There is also a MNDOC method that includes electron correlation. 

MNDOC has the same functional form as MNDO, however, electron correlation is explicitly calculated by second-order perturbation theory. The derivation of the MNDOC parameters is done by fitting the correlated MNDOC results to experimental data. Electron correlation in MNDO is only included implicitly via the parameters, from fitting to experimental results. Since the training set only includes ground-state stable molecules, MNDO has problems treating systems where the importance of electron comelation is substantially different from normal molecules. MNDOC consequently performs significantly better for systems where this is not the case, such as transition structures and excited states. 

The semiempirical molecular orbital (MO) methods of quantum chemistry [1-12] are widely used in computational studies of large molecules. A number of such methods are available for calculating thermochemical properties of ground state molecules in the gas phase, including MNDO [13], MNDOC [14], MNDO/d [15-18], AMI [19], PM3 [20], SAMI [21,22], OM1 [23], OM2 [24,25] MINDO/3 [26], SINDOl [27,28], and MSINDO [29-31]. MNDO, AMI, and PM3 are widely distributed in a number of software packages, and they are probably the most popular semiempirical methods for thermochemical calculations. We shall therefore concentrate on these methods, but shall also address other NDDO-based approaches with orthogonalization corrections [23-25],... 

A unified theoretical explanation using molecular orbital theory has been proposed. Grimme [65] investigated the PFR of phenyl acetate as well as the photo-Claisen rearrangement of allyl phenyl ether and the 3-cleavage of para-substituted phenoxyacetones. A unified description of the three reactions has been invoked according to MNDOC-CI and AMl/AMl-HE calculations. No matter what ex-... 

MNDOC MNDO including electron correlation effects... 

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... 

Schroder and Thiel have compared MNDO (Section 6.2.5.3) and MNDOC (Section 6.2.5.7) with ab initio calculations for the study of the geometries and energies of 47 transition states [47]. AMI and PM3 calculations should give somewhat better results than MNDO for these systems, since these two methods... 

Tel. 913-268-3271, fax 913-268-3445, e-mail aholder vaxl.umkc.edu Semiempirical molecular orbital calculations with M. J. S. Dewar s SAMI parameterization, including d orbitals for transition metals, and a graphical user interface. MINDO/3, MNDO, MNDOC, AMI, and PM3 methods. DEC, Cray, Silicon Graphics, Sun, and PCs (under X-Windows). 

MNDOC has the same functional form as MNDO, however, electron correlation is explicitly calculated by second-order perturbation theory. The derivation of the MNDQC... 

These results also follow from the cross sections through the potential energy surfaces calculated in the semiempirical all-valence electron approximation by the MNDOC-CI method for acetaldehyde, acrolein, and benzal-dehyde, which are displayed in Figure 7.13. Stabilization of the state... 

Bachmann, C., N Guessan, T. Y., Debu, F., Monnier, M., Pourcin, J., Aycard, J. P., Bodot, H. Oxirenes and ketocarbenes from a-diazoketone photolysis experiments in rare gas matrices. Relative stabilities and isomerization barriers from MNDOC-BWEN calculations. 

W. Thiel, The MNDOC method, a correlated version ofthe MNDO model, J. Am. Chem. Soc. 103, 1413-1420(1981). 

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