Simulated Ab Initio Molecular Orbital Research Articles

The simulatedab initio molecular orbital (SAMO) method. VIII. A study of linear polyfluoroethylenes and polychloroethylenes

The simulated ab initio molecular orbital (SAMO) method band structures of six fluorinated and six chlorinated polymers derived from linear polyethylene are presented and compared with extended Huckel and CNDO/2 studies and with the results of ESCA spectroscopy.

Comparison of SAMO and a b i n i t i o model calculations for pyrazine

The simulated ab initio molecular orbital (SAMO) technique and the ab initio model calculation of Butkus and Fink are compared for the pyrazine molecule. Both methods construct the wave function of pyrazine from wave functions of smaller pattern molecules. The methods are complimentary in that the strengths of one are often the weakness of the other. The SAMO method gives good orbital energies which are not given by the ab initio model method, while the latter is more readily extended to the ionic protonated molecules.

The simulated ab initio molecular orbital (samo) method: Application To Second-Row Elements

The simulated ab initio molecular orbital (SAMO) method is extended to molecules containing second-row atoms with d-orbitals included in the basis. Results for 1-butanethiol are as successful as previous studies for molecules containing only first-row atoms. The role of hybrid orbitais is critically discussed.

A combined SAMO-ZDO method for the evaluation of ionization potentials

A scheme for the ab initio calculation of vertical ionization potentials without the necessity to compute two-electron repulsion integrals is discussed. The method employs the simulated ab initio molecular orbital (SAMO) method to generate Koopman's theorem eigenvalues. These are then corrected for the change in relaxation and correlation effects due to ionization by a Green's function perturbation scheme, in which all necessary integrals are evaluated using the zero differential overlap (ZDO) approximations, in this case the complete neglect of differential overlap (CNDO) method.

The simulated ab initio molecular orbital technique. VI. Open‐shell radicals in the spin restricted formalism

AbstractThe simulated ab initio molecular orbital (SAMO) method previously applied to RHF closed‐shell and UHF open‐shell situations has been applied to open‐shell radicals, such as the butyl radical and the pentyl radical, within the RHF open‐shell framework. The open‐shell Hartree–Fock theory is developed such that a rapidly convergent iterative method for evaluating the SAMO wave‐function can be employed. Results closely parallel those for the same systems using the UHF method and are of comparable accuracy to SAMO closed‐shell results.

The simulated ab initio molecular orbital method for polymers polyglycine

The simulated ab initio molecular orbital (SAMO) method is here applied to polyglycine — the simplest polymer of biochemical interest. Results are compared with semi-empirical methods and experiment.

Simulated ab initio molecular orbital technique. Part 5.—Polar groups, ionic molecules and orthogonalised basis sets

The previously reported simulated ab initio molecular orbital (SAMO) method is extended in several ways. First, the application to polar molecules is demonstrated for the first time. The systems studied are RX, where X = OH, NH2, CHO or COOH and R is an alkyl group. Results are at least as good as for the non-polar molecules previously studied. Secondly, a simple extension is developed for RX molecules where X is ionic. For these systems the simple method is inapplicable. Finally, the use of an orthogonalised basis is described and found to be less successful than expected.

Resolvent method for quantitative calculations of ab-initio type wavefunctions for large molecules. I. General theory for the SAMO technique

The Koster-Slater equations for impurities in solids are applied to the simulated ab-initio molecular orbital (SAMO) method. The secular equations are thereby reduced in size, enabling one to calculate SAMO wavefunctions for large polyatomic systems. A method of solving the resulting equations is described.

Avoiding the use of integral lists in the ab initio LCAO SCF MO method

The suggestion is made that the storage of long lists of two-electron repulsion integrals in the LCAO SCF MO method could be avoided if such integrals were evaluated at each SCF cycle and an initial set of eigenvectors were available to lead to rapid convergence. Results are presented showing that the simulated ab initio molecular orbital (SAMO) technique provides an excellent set of initial eigenvectors for the SCF procedure.

Simulated ab initio molecular orbital technique. Part 3.—Open shell radicals in the spin unrestricted formalism

The simulated ab initio molecular orbital (SAMO) technique, previously applied to closed-shell situations has now been applied to open-shell radicals such as the butyl radical and the pentyl radical. The odd electron here is localised in one region of the molecule. The method employs the spin-unrestricted formalism and results are compared with full ab initio calculations using the same approach. It is shown that an adequate simulation can be achieved by combining transferability of matrix elements from smaller open-shell radicals and smaller closed-shell molecules.

The simulated ab-initio molecular orbital (SAMO) method for polymers. Polyethylene and polyene

The application of the simulated ab-initio molecular orbital (SAMO) method — a new non-empirical technique — to the band structure of polymers is reported. The method uses full ab-initio results on small molecules to construct for polymers molecular orbitals which simulate those obtained from full ab-initio treatments. Results are compared with those obtained from published ab-initio and semi-empirical calculations.