Molecular orbital semiempirical methods

Type B3LYP B3PW91 B3P86 BLYP BPW91 BP86 SVWN 

The third approach is the complete neglect of differential overlap approximation (CNDO), in which only the one- and two-center, two-electron integrals remain. The direct application of these methods (NDDO, INDO, or CNDO) is not useful because of the approximations, so it is necessary to include parameters in place of all or some of the integrals. These parameters are based on atomic or molecular experimental data. 

Several versions of modified INDO (MINDO) that employ such a parameterization have been proposed. These include MINDO/1, MINDO/2, MINDO/2, and MINDO/3, only the last of which resulted in a quantum chemical program that was widely used. MINDO/3151 is parameterized for H, B, C, N, O, F, Si, P, S, and Cl, although certain combinations of these atoms are not parameterized. The MINDO/3 method is no longer heavily used because the parameterized NDDO methods are generally more accurate. 

Various parameterizations of NDDO have been proposed. Among these are modified neglect of diatomic overlap (MNDO),152 Austin Model 1 (AMI),153 and parametric method number 3 (PM3),154 all of which often perform better than those based on INDO. The parameterizations in these methods are based on atomic and molecular data. All three methods include only valence s and p functions, which are taken as Slater-type orbitals. The difference in the methods is in how the core-core repulsions are treated. These methods involve at least 12 parameters per atom, of which some are obtained from experimental data and others by fitting to experimental data. The AMI, MNDO, and PM3 methods have been focused on ground state properties such as enthalpies of formation and geometries. One of the limitations of these methods is that they can be used only with molecules that have s and p valence electrons, although MNDO has been extended to d electrons, as mentioned below. 

The performance of the semiempirical methods for the calculation of thermochemical data depends on the extent to which the physics is included in the model and how well the neglected features can be accounted for by the parameterization. These methods can be assessed by validation against accurate experimental data or high level ab initio predictions. A summary of results for four semiempirical methods (MINDO/3, MNDO, AMI, and PM3) for the neutral enthalpies of formation in the G2/97 test set is given in Table 13. Overall, the newest method, PM3, does the best with an average absolute deviation of 7.02 kcal/mol. It has average absolute deviations of 3.91 and 4.27 kcal/mol for the subgroups of hydrocarbons and substituted hydrocarbons, respectively. 

The Frank J. Seiler Research Laboratory, United States Air Force Academy, Colorado 80840 

There are currently three commonly employed theoretical methods for the study of the properties of molecules. Here we will look at semiempirical methods, which occupy a position between the ah initio and molecular mechanics methods. High level ab initio methods have an accuracy comparable with experiments for heats of formation and are at least as accurate as experiments for the determination of molecular geometries. They are also versatile enough to allow transition states and excited states to be calculated. The only drawback to high level cUj initio work is the cost in terms of computer resources. 

On the other hand, molecular mechanics (MM) methods are extremely fast and are able to handle very large systems, such as entire enzymes, with ease. Some MM methods are also as accurate as the best ab initio methods, particularly for hydrocarbons. Unfortunately, MM methods are usually parameterized only for ground state systems as a result they are unable to adequately represent the geometries involved in bond making-bond breaking processes. 

Between the two are the semiempirical methods. Like molecular mechanics methods, they use experimentally determined parameters like ab initio methods, they are basically quantum mechanical in nature, with the main difference between semiempirical and ab initio methods being the extensive use of approximations in the semiempirical approach. This allows semiempirical methods to avoid the need to evaluate the large number of terms used 

In this chapter, we will look at a few commonly used semiempirical methods and see how they evolved. Very recently a comprehensive summary of the status of semiempirical methods, with the emphasis on MNDO and its relationship with more rigorous methods, was published. The review of semiempirical methods given here is intended to complement Professor Thiel s article by being less formal. Students of semiempirical methods are strongly advised to refer also to ref. 1. 

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Stewart J J P 1991 Semiempirical molecular orbital methods Reviews in Computationai Chemistry vo 1, ed K B Lipkowitz and D B Boyd (New York VCH) pp 45-81... 

Stewart HP. Semiempirical molecular orbital methods. In Lipkowitz KB, Boyd DB, editors. Reviews in Computational Chemistry, Vol. 1. New York VCH, 1990. p. 45-81. 

James J. P. Stewart, Semiempirical Molecular Orbital Methods. 

More advanced semiempirical molecular orbital methods have also been used in this respect in modeling, e.g., the structure of a diphosphonium extractant in the gas phase, and then the percentage extraction of zinc ion-pair complexes was correlated with the calculated energy of association of the ion pairs [29]. Semiempirical SCF calculations, used to study structure, conformational changes and hydration of hydroxyoximes as extractants of copper, appeared helpful in interpreting their interfacial activity and the rate of extraction [30]. Similar (PM3, ZINDO) methods were also used to model the structure of some commercial extractants (pyridine dicarboxylates, pyridyloctanoates, jS-diketones, hydroxyoximes), as well as the effects of their hydration and association with modifiers (alcohols, )S-diketones) on their thermodynamic and interfacial activity [31 33]. In addition, the structure of copper complexes with these extractants was calculated [32]. 

In this paper, we make use of molecular modelling techniques, particularly the AMI semiempirical molecular orbital method, to study the intermolecular interactions that are important for determining the manner in which crystal formation takes place. We are particularly inter ested in compounds that can potentially exhibit nonlinear optical properties. The calculational techniques are directed towards providing insight into the manner in which the desired nonlinear optical properties can be op timized in the macromolecular crystal state.(1)... 

AI, ab initio molecular orbital methods DF, density functional methods SE, semiempirical molecular orbital methods FF, force field methods. 

Semiempirical molecular orbital methods23-25 incorporate parameters derived from experimental data into molecular orbital theory to reduce the time-consuming calculation of two-electron integrals and correlation effects. Examples of semiempirical molecular orbital methods include Dewar s AMI, MNDO, and MINDO/3. Of the three quantum chemical types, the semiempirical molecular orbital methods are the least sophisticated and thus require the least amount of computational resources. However, these methods can be reasonably accurate for molecules with standard bond types. 

During the early years at McGill University, Whitehead s group concentrated on experimental nuclear quadrupole resonance spectroscopy123 and a variety of n- and all-valence electron semiempirical molecular orbital methods.124 His recent interests have included topics as diverse as density functional theory125 and related topics,126 and molecular models of surfactants. 

Drs. Larry A. Curtiss, Paul C. Redfern, and David J. Frurip present a tutorial on how to compute enthalpies of formation in Chapter 3. Often a computational chemist will want to know how stable a molecule is. The techniques described in this chapter can answer this question. The authors, who have studied what has been called computational thermochemistry, describe ab initio molecular orbital methods (including the highly accurate and popular Gn methods), density functional methods, semiempirical molecular orbital methods, and empirical methods (such as based on bond energies). These methods are richly illustrated with detailed, worked out examples. 

Tehan, B.G., Lloyd, E.J., Wong, M.G., Pitt, W.R., Montana, J.G., Manallack, D.T. and Gancia, E. (2002). Estimation of pKa using semiempirical molecular orbital methods, part 1 application to phenols and carboxylic acids. Quant Struct-Act Relat, 21, 457-472. 

V. A. Gubanov, V. P. Zhukov, and A. O. Litinskii, Semiempirical Molecular Orbital Methods in Quantum Chemistry, Nauka, Moscow, 1976. 

Serban Moldoveanu and Andrei Savin, Chemical Applications of the Semiempirical Molecular Orbital Methods, Ed. Acad. Rep. Soc. Rom., Bucharest, 1980. 

Probably, Mike s research has most touched other scientists through his development of ZINDO, the semiempirical molecular orbital method and... 

Zerner MC (1990) Semiempirical molecular orbital methods. In Lipkowitz KB Boyd DB (eds) Reviews of computational chemistry, VCH, New York, vol 25, p. 313... 

Boyd, Eds., VCH Publishers, New York, 1990, pp. 45-81. Semiempirical Molecular Orbital Methods. 

VCH Publishers, New York, 1990, Vol. 1, pp. 45-81. Semiempirical Molecular Orbital Methods. M. C. Zerner, in Reviews in Computational Chemistry, K. B. Lipkowitz andD. B. Boyd, Eds., VCH Publishers, New York, 1991, Vol. 2, pp. 313-365. Semiempirical Molecular Orbital Methods. 

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