SCF-CI calculations

It has been proposed that the formation of these species probably involves a coordination of SnR4 to the Pt surface to form a pentacoordinated Sn intermediate (Scheme 33) [117]. This proposed step is based on a detailed study using SCF(CI) calculations [118] on the interaction between Sn(CH3)4 and a reduced Rhi3H2o cluster. The formation of this intermediate induces the weakening of the Sn - C bond [119], which would fadhtate the formation of the Sn - Ms bond. 

SCF-CI calculations were performed at 20 different intemuclear separations, from 1.2 bohr to 4-00. The lowest separate atom states are, B( P,2p) and H( S) therefore, in order to have a homolytic dissociation and three degenerate 2p orbitals on B we have adopted the closed shell Fock hamiltonian with fractional occupation [23] one electron was placed in the 3(t orbital, correlating with H(ls) at infinite separation, and 1/3 each in the 4it and Itr orbitals correlating with B(2p). 

Bond-order changes upon photoexcitation obtained from Sandorfy SCF-CI calculations have been employed to predict the ease of photoextrusion of a silylene from polysilane chains or rings236. Smaller bond-order changes with longer polysilane chains suggested that they are less efficient silylene sources. Similar conclusions were reached for branched and cyclic polysilanes. This approach focuses on a to a excitation without participation by Si 4s orbitals in descriptions of excited states237. 

Desouter-Lecomte, M., Dehareng, D., and Lorquet, J.C. (1987). Constructing approximately diabatic states from LCAO-SCF-CI calculations, J. Chem. Phys. 86,1429-1436. 

SCF-CI calculations have also been carried out for Ne-----Ne 39 in much the same... 

GVB calculations on CHa have also been reported,449 so a value of 134 + 2° seems well established. Other SCF-CI calculations on the low-lying states have been reported,450 and it now seems clear that the HCH angle in the ground state is 134 2°. 

This bond order control is seen even in Huckel17,18) and SCF 23) calculations on the 3,5-cyclohexadienone system. Although there are definite quantitative and other advantages to the use of SCF and SCF-CI calculations in organic chemistry, Huckel theory very frequently provides a reward in simplicity and in allowing one to understand the basic factors giving rise to some phenomenon. In the present instance, reference to Fig. 5 12-n.18,20 anows ready understanding of the n-rc P,P-bond order and its contrast with the n-n excited state. 

One way to generate surfaces is by explicit QM calculation of species as they are followed through some mechanism. SCF-CI calculations have proven of considerable value in the author s research. The philosophy here has been to include as basis orbitals only those atomic and hybrid orbitals which are part of chromo-phores or make up bonds which are altered, broken, formed or modified, during the photochemical transformation. Additionally, basis orbitals aimed along the directions of bonds are used, since then the SCF wavefunctions are linear combinations of recognizable orbitals of bonds rather then arbitrary vertically and horizontally oriented atomic orbitals. 

Figure 1. Potential energy surfaces as a function of bond angle for Lis, Lis and Lis " obtained from SCF-CI calculations at a bond distance of 5.6 a.u. a Cut in surfaces for Lis nd Lis. Key A, Lis, O, Lis Ai and %, Lis A2(Dsii). Various vertical electron affinities are represented, b Cut in surfaces for Lis nd Lis". Key O, Lis cind A, Lis". Various vertical ionization potentials are represented. Dissociation to Li + U2" at 5.24 eV (A).

A fuller account of the poly atom code was published in 1966 by Csizmadia, Harrison, Moskowitz and Sutcliffe in a paper entitled Non-Empirical LCAO-MO-SCF-CI Calculations on Organic Molecules with Gaussian Type Functions. Part I. Introductory Review and Mathematical Formalism . This was followed immediately... 

Purely quantum studies of the fully coupled anharmonic (and sometimes nonrigid) rovibrational state densities have also been obtained with a variety of methods. The simplest to implement are spectroscopic perturbation theory based studies [121, 122, 124]. Related semiclassical perturbation treatments have been described by Miller and coworkers [172-174]. Vibrational self-consistent field (SCF) plus configuration interaction (Cl) calculations [175, 176] provide another useful alternative, for which interesting illustrative results have been presented by Christoffel and Bowman for the H + CO2 reaction [123] and by Isaacson for the H2 + OH reaction [121]. The MULTIMODE code provides a general procedure for implementing such SCF-CI calculations [177]. Numerous studies of the state densities for triatomic molecules have also been presented. 

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