Semi-empirical molecular orbital

Presell is the basic theory of tjuaiiHim mechanics, particularly, semi-empirical molecular orbital theory. The authors detail and justify the approximations inherent in the semi-empirical Ham illoTi ian s. Includes useful discussion s of th e appiicaliori s of these methods to specific research problems. 

Most simple empirical or semi-empirical molecular orbital methods. including all ofthose ii sed in IlyperCh em, neglect inner sh ell orbitals and electrons and use a minimal basis se.i r>f valence Slater orbitals. 

Schaeffer H F III (Editor) 1977. Applications of Electronic Structure Theory. New York, Plenum Press. Schaeffer H F III (Editor) 1977. Methods of Electronic Structure Theory. New York, Plenum Press. Stei. art J J P 1990. MOP AC A Semi-Empirical Molecular Orbital Program. Journal of Computer-Aided Molecular Design 4 1-45. 

Stewart)) P1990. Semi-empirical Molecular Orbital Methods. In Lipkowitz K B and D B Boyd (Editors). 

These atomic orbitals, called Slater Type Orbitals (STOs), are a simplification of exact solutions of the Schrodinger equation for the hydrogen atom (or any one-electron atom, such as Li" ). Hyper-Chem uses Slater atomic orbitals to construct semi-empirical molecular orbitals. The complete set of Slater atomic orbitals is called the basis set. Core orbitals are assumed to be chemically inactive and are not treated explicitly. Core orbitals and the atomic nucleus form the atomic core. 

In all these examples, the importance of good simulation and modeling cannot be stressed enough. A variety of methods have been used in this field to simulate the data in the cases studies described above. Blander et al. [4], for example, used a semi-empirical molecular orbital method, MNDO, to calculate the geometries of the free haloaluminate ions and used these as a basis for the modeling of the data by the RPSU model [12]. Badyal et al. [6] used reverse Monte Carlo simulations, whereas Bowron et al. [11] simulated the neutron data from [MMIM]C1 with the Empirical Potential Structure Refinement (EPSR) model [13]. 

These major trends in act can be qualitatively predicted using semi-empirical molecular orbital calculations. However, the methods fail to adequately predict some electronic effects, remote substituent effects and the influence of hydrogen bonding. Higher level ah initio or DFT calculations provide a better indication of trends in these circumstances. 

Semi-empirical molecular orbital calculations have been carried out on the model phosphorane HaPiCHa. Besides the expected transfer of charge, the inclusion of the phosphorus 2>d orbitals showed a significant hyperconjugative interaction between the CHg orbitals and a 2>d orbital of appropriate symmetry on phosphorus. Calculations on cyclopropylidene-phosphorane revealed a similar interaction between the Walsh orbitals of the ring and an in-plane phosphorus 2>d orbital. 

Semi-empirical molecular orbital calculations on the phosphorane (96)... 

TOWARDS AN ACCURATE SEMI-EMPIRICAL MOLECULAR ORBITAL TREATMENT OF COVALENT AND NON-COVALENT BIOLOGICAL INTERACTIONS... 

The absorption bands measured by the flash spectrographic method are often assigned by (a) comparison with known singlet-singlet absorption spectra, (b) comparison of the lifetime of the species responsible for the absorption with the phosphorescence lifetime, (c) comparison with calculated energies and intensities of the various possible absorptions by semi-empirical molecular orbital methods, and (d) comparison with published triplet absorption spectra and decay kinetics of model compounds. 

Geometric Optimization. The structure of the molecule as built by CHEMLAB (or a input from other methods) can be optimized through either a full force field molecular mechanics calculation (MMII) or with the semi-empirical molecular orbital methods MINDO-3 and MNDO. 

Molecular Energetics. Molecular energies can be computed in a variety of ways including empirical fixed valence potentials, full force field potentials, and semi-empirical molecular orbital techniques (CNDO-2, INDO, MINDO-3, MNDO, PCILO). 

Co2(CO)q system, reveals that the reactions proceed through mononuclear transition states and intermediates, many of which have established precedents. The major pathway requires neither radical intermediates nor free formaldehyde. The observed rate laws, product distributions, kinetic isotope effects, solvent effects, and thermochemical parameters are accounted for by the proposed mechanistic scheme. Significant support of the proposed scheme at every crucial step is provided by a new type of semi-empirical molecular-orbital calculation which is parameterized via known bond-dissociation energies. The results may serve as a starting point for more detailed calculations. Generalization to other transition-metal catalyzed systems is not yet possible. 

Ionization potentials calculated for cyclopentadienide ions (1 -8 ) by a semi-empirical molecular-orbital method (AMI) correlate with the observed electron... 

For more semi-empirical molecular orbital calculations and comparison with experimental data, see Section 4.01.2. For MO calculations on aromaticity and tautomerization, see Section 4.01.3. 

Fenske, R. F. Semi-empirical molecular-orbital theory for transition-metal complexes. Inorg. Chem. 4, 33 (1965). 

Of the Ru(IV) complexes recorded here most are mono-oxo species which, despite the strong axial distortion brought about by the terminal oxo ligand, are probably all paramagnetic. Semi-empirical molecular orbital calculations (INDO/1) for epoxidations effected by oxo-Ru(IV) complexes have been reported (a non-concerted [1 h- 2] pathway was preferred) [642], [643] and for alcohol oxidations by octahedral species containing an Ru" (0) unit [644]. The reactivity of high oxidation-state polypyridyl complexes of osmium and Ru, with particular emphasis on Ru(IV) and Os(IV) oxo species, has been reviewed [43]. 

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