Self-consistent field theory qualitative theories

Theoretical calculations of minimum-energy structures and thermodynamic terms using self-consistent field theory with thermodynamic and solvation corrections concluded that the cyclization of l-hydroxy-8-(acetylamino)naphtha-lene 1 to give 2-methylnaphth[l,8-r7,< ][l,3]oxazine 2 with the liberation of water was much less favorable (AG = —2.0kj moP, A/7 = 4-31.0kj mol , and TAS = 4-33.1 kjmoP at 298.2 K) in the gas phase than the corresponding ring closure of l-amino-8-(acetylamino)naphthalene, which was in qualitative agreement with experimental observations for the reactions in solution <1998J(P2)635>. 

As mentioned earlier, studies of simple linear surfactants in a solvent (i.e, those without any third component) allow one to examine the sufficiency of coarse-grained lattice models for predicting the aggregation behavior of micelles and to examine the limits of applicability of analytical lattice approximations such as quasi-chemical theory or self-consistent field theory (in the case of polymers). The results available from the simulations for the structure and shapes of micelles, the polydispersity, and the cmc show that the lattice approach can be used reliably to obtain such information qualitatively as well as quantitatively. The results are generally consistent with what one would expect from mass-action models and other theoretical techniques as well as from experiments. For example. Desplat and Care [31] report micellization results (the cmc and micellar size) for the surfactant h ti (for a temperature of = ksT/tts = /(-ts = 1-18 and... 

The dynamic self-consistent field theory has been widely used in the form of MESODYN [97]. This scheme has been extended to study the effect of shear on phase separation or microstructure formation, and to investigate the morphologies of block copolymers in thin films. In many practical applications, however, rather severe numerical approximations (e.g., very large discretization in space or contour length) have been invoked, that make a quantitative comparison to the the original model of the SCF theory difficult, and only the qualitative behavior could be captured. 

However, despite their proven explanatory and predictive capabilities, all well-known MO models for the mechanisms of pericyclic reactions, including the Woodward-Hoffmann rules [1,2], Fukui s frontier orbital theory [3] and the Dewar-Zimmerman treatment [4-6] share an inherent limitation They are based on nothing more than the simplest MO wavefunction, in the form of a single Slater determinant, often under the additional oversimplifying assumptions characteristic of the Hiickel molecular orbital (HMO) approach. It is now well established that the accurate description of the potential surface for a pericyclic reaction requires a much more complicated ab initio wavefunction, of a quality comparable to, or even better than, that of an appropriate complete-active-space self-consistent field (CASSCF) expansion. A wavefunction of this type typically involves a large number of configurations built from orthogonal orbitals, the most important of which i.e. those in the active space) have fractional occupation numbers. Its complexity renders the re-introduction of qualitative ideas similar to the Woodward-Hoffmann rules virtually impossible. 

Various theoretical methods and approaches have been used to model properties and reactivities of metalloporphyrins. They range from the early use of qualitative molecular orbital diagrams (24,25), linear combination of atomic orbitals to yield molecular orbitals (LCAO-MO) calculations (26-30), molecular mechanics (31,32) and semi-empirical methods (33-35), and self-consistent field method (SCF) calculations (36-43) to the methods commonly used nowadays (molecular dynamic simulations (31,44,45), density functional theory (DFT) (35,46-49), Moller-Plesset perturbation theory ( ) (50-53), configuration interaction (Cl) (35,42,54-56), coupled cluster (CC) (57,58), and CASSCF/CASPT2 (59-63)). 

It is important to emphasize from the outset that metal-metal bonds present a substantirJ challenge to electronic structure theory, particularly where diatomic overlap is weak and the electrons are highly correlated. The chromium dimer, Crj, for example, is a notoriously difficult case and has been the subject of debate for decades [13], Some progress toward a quantitative understanding of these correlation effects has been made through Complete Active Space Self Consistent Field (CASSCF) and related wavefunction-based techniques, but much of our qualitative understanding... 

In an interdisciplinary volume such as the present, it does not seem appropriate to give any sort of detailed coverage to the theoretical methods currently in use (, 7 ). It must be noted, however, that the Hartree-Fock or Self-Consistent-Field (SCF) method remains at the core of electronic structure theory. Although SCF theory is sometimes adequate in describing potential energy surfaces, this has turned out more often not to be the case. That is, electron correlation, which incorporates the instantaneous repulsions of pairs of electrons, can have a qualitative effect on the topology of fluorine hydrogen potential surfaces. 

Reaction field theory with a spherical cavity, as proposed by Karlstrom [77, 78], has been applied to the calculation of the ECD spectrum of a rigid cyclic diamide, diazabicyclo[2,2,2]octane-3,6-dione, in an aqueous environment [79], In this case, the complete active space self-consistent field (CASSCF) and multiconfigurational second-order perturbation theory (CASPT2) methods were used. The qualitative shape of the solution-phase spectrum was reproduced by these reaction field calculations, although this was also approximately achieved by calculations on an isolated molecule. 

Buenker, Robert J., Peyerimhoff, Sigrid D., 8c Hsu, Kang. 1971. "Analysis of Qualitative Theories for Electrocyclic Transformations Based on the Results of Ab Initio Self-Consistent-Field and Configuration-Interaction Calculations." Journal of the American Chemical Society 93 5005-5013. 

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