Dewar, Michael, semiempirical methods

The current status of the semiempirical methods pioneered by Michael J. S. Dewar is given. These methods are made available to non—theoreticians through the programs MOP AC and AMPAC. Some capabilities of MOPAC and the form of the data input to the program are outlined. 

The MOPAC program (Molecular Orbital PACkag) (26) Is one of the popular quantum mechanical semiempirical methods. The AM1 (Austin Model 1), developed by Michael Dewar (26), is a generalization of the modified neglect of differential diatomic overlap (MNDO) approximation. Often, AM1 is implemented in the MOPAC, and MOPAC(AMt) has been widely used to minimize molecular conformations, to calculate electronic configuration, and to predict such properties as electron distribution and partial charges. 

In Pople s career in computational chemistry he was first instrumental in the introduction and dissemination of semiempirical techniques, and contributed to the development of a whole set of successful methods that gained broad acceptance and applications. Here we mention only two of the several major figures in addition to Pople who contributed greatly to the development and spreading of semiempirical methods, Robert G. Parr (Fig. 1.16a) and Michael Dewar (Fig. 1.16b). 

Ground States of Molecules XXV MINDO/3. An Improved Version of the MINDO Semiempirical SCF-MO Method Richard C. Bingham, Michael J. S. Dewar and Donald H. Lo Journal of the American Chemical Society 97 (1975) 1285-1293... 

Some functionals, in particular B3LYP, incorporate parameters that are optimized by comparisons between DFT and experimental results. Thus, B3LYP calculations are, like the MINDO, MNDO, and AMI methods that were developed by the late Michael Dewar in the 1970s and 1980s, semiempirical in nature. In this sense, B3LYP could be called the AMI of the twenty-first century . 

By the early 1970s, molecular mechanics computer programs such as MMI and MM2 were available, running on the IBM 360. For proteins, ECEPP was developed by Harold A. Scheraga. - Countering the molecular mechanics approach, Michael J. S. Dewar modified John A. Pople s (complete) neglect-of-differential-overlap semiempirical quantum mechanical method (CNDO/2) to calculate quantities such as conformational stability and heats of formation. Such programs (MNDO) were necessarily slower than the empirical force field methods such as MM2 and ECEPP but still had fewer parameters and could account for the effects of polarization in aromatic systems. 

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