Effective Hamiltonian technique

Using a valence bond scheme parametrized with an effective Hamiltonian technique, it was shown that the mechanistic preference for a synchronous pathway with an aromatic transition state versus a non-synchronous mechanism via biradicaloid intermediate can be controlled by two factors (1) the stability of the long bond in the Dewar valence bond structure, and (2) the softness of the Coulomb interaction between the end methylene groups in the 1,5-diene chain. This means that the mechanism of rearrangement (equation 153) can strongly depend on substituents218. 

We have employed the recently developed Valence Effective Hamiltonian technique (16) and MNDO calculations (22) to study the influence of strain in TKe sidegroups on the geometry of the backbone and the resulting polymer band structure, bandgap, and ionization potential. The molecule used in our simulation of strain... 

The electrochemical properties of conductive polymer systems are important with regard to understanding the electrochemical doping process and in applications of conductive polymers as battery electrodes. We have developed a computational method, based on the Valence Effective Hamiltonian technique, which is remarkably effective in the computation of oxidation and reduction potentials of a variety of conjugated polymers (polyacetylene, polyphenylene, polythiophene, polypyrrole) and their oligomers. 

A Bloch-type effective Hamiltonian technique in a CI /SO method simply amoimts to replace the diagonal energy of the intermediate model space by the fiall correlated one, Em, coming from the target space of the first step calculation, without knowing — at least in principle — the corresponding wave... 

Taking /SEk instead of Ek only amounts to choose the ground state as origin for the energy. Llusar et al showed by calculations of a MgO-embedded (Ni06) cluster, that the effective Hamiltonian technique applied on the spin-free part of the Hamiltonian, significantly improves the spin-orbit splitting. 

Calculated on PQ using the Valence Effective Hamiltonian Technique (VEH)... 

Bredas, J. L., Themans, B., and Andre, J. M., Valence effective Hamiltonian technique for nitrogen-containing polymers electronic structure of polypyrrole, pyrolized polyacrylonitrile and derivates, Phys. Rev. B, 27, 7827-7842 (1983). 

Bredas, J. L., Chance, R. R., Silbey, R., Nicolas, G., and Durand, P. A. "Nonempirical Effective Hamiltonian Technique for Polymers Application to Polyacetylene and Polydiacetylene." /. Chem. Phys., 75,255-267(1981). 

Bredas, J.L., R.R.Chance,R.Silbey,G.Nicolas and Ph. Durand. A Nonempirical Effective Hamiltonian Technique for Polymers Application to Polyacetylene and Polydiacetylene, J.Chem.Phys. 75 (1981) 255... 

The availability of detailed information about the electronic states of PDAs makes them ideal systems to test molecular quantum mechanical theories. The earliest calculation for a model PDA chain with simple sidegroups gave rather poor values for the band-gap, see (7). In most of these calculations Coulomb correlations were neglected so that only band structures were deduced. Further work along these lines has included the use of an ab initio crystal orbital method [105), studies of the ground state geometries [106), a priori Hartree Fock crystal orbital calculations (107) and a non-empirical effective Hamiltonian technique [108). These show... 

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