LCAO-MO-SCF

Csizmadia I G, Flarrison M C, Moscowitz J Wand Sutcliffe B T 1966 Commentationes. Non-empirical LCAO-MO-SCF-Cl calculations on organic molecules with Gaussian type functions. Part I. Introductory review and mathematical formalism Theoret. Chim. Acta 6 191-216... 

The basis orbitals eommonly used in the LCAO-MO-SCF proeess fall into two... 

The inductive and electrostatic effects, steric constraints and conjugative interactions are the major factors that determine the configurational stability of a-sulfonyl carbanions. These are thought to be pyramidal with appreciable electrostatic inhibition to racemization by way of inversion. LCAO-MO-SCF calculations have indicated the conformer 195 in which the lone pair is directed along the bisector of the OSO angle to be the most stable in acyclic sulfones. ... 

Steiger et al. (205) suggested the Coni-02- structure based on femtosecond dynamics. Molecular orbital diagrams (24,25) and earlier LCAO-MO-SCF calculations (29) support this assignment. No ab initio or DFT results on the electronic structure of CoP-02 have been reported so far. 

There have been several ab imto LCAO MO SCF calculations on tetrahedral transition-metal complexes for example, see the work of Hillier and Saunders (Molecular physics 22, 1025 (1970)), and Demuynck and Veillard (Theoretica chimica acta 28, 241 (1973)) on nickel carbonyl Ni(OO). ... 

The 7r-electronic structure and electronic spectra of dithiocarbamic acid, HjDtcH, previously analyzed by Janssen (360) and Fabian (228), were reexamined by St. Nikolov and Tyutyulkov (585). In this later study calculations were carried out by the LCAO—MO—SCF-CI method. Excellent agreement between the calculated and observed energies of the two electronic transitions at 34.6 and 39 kK was reported. By an analysis of the -electronic charge densities, occurring on excitation, it was concluded that these two electronic transitions are located mainly on the CS2 group. 

Theoretical studies for the 1,1-dithio complexes of the extended Hiickel or LCAO-MO--SCF type are few, and accounts of such studies are briefly given in the appropriate sections, which are arranged according to element. 

A LCAO—MO—SCF calculation on the Ni(H2Dtc)2 and Ni—(PhDta)2 complexes is available (123). In this calculation the participation of the 4s and 4px orbitals in the ground state was found to be small. Furthermore, there was no participation of the Apy and 4pz orbitals. 

A. C. Hopkinson, N. K. Holbrook, K. Yates, and I. G. Csizmadia,/. Chem. Phys., 49, 3596 (1968). Theoretical Study on the Proton Affinity of Small Molecules Using Gaussian Basis Sets in the LCAO-MO-SCF Framework. 

As (CH3)3P=CH2 is still too formidable a problem for theoretical chemists, the related but hypothetical H3P=CH2 molecule was the subject of the ab initio LCAO-MO-SCF studies published in 1972 (1). Using two uncontracted Gaussian basis sets, one with and the other without phos-... 

The tortuous process of ab initio LCAO-MO-SCF calculation, the flagship of computational chemistry, has been the subject of interminable reviews, e.g. [15], and will be described here in the briefest of outlines. 

Kaufman, J. Semirigorous LCAO-MO-SCF methods for three-dimensional molecular calculations including electron repulsion. J. Chem. Phys. 43, 152 (1965). 

Early Examples of Surface Calculations for Closed-shell Systems.—The first LCAO-MO SCF calculation of a reaction pathway on a potential surface for a reaction between two closed-shell species was performed by Clementi" for the system NHa + HC1 to form NH4CI. The calculation employed contracted sets of GTO s (llf,7p)- [5j,3p] for N, (6s,p) [3s,p for H and (llr,7p)— [5r,4p] for Cl. Since the basis set does not contain any polarizing functions on the N and Q centres, it will not yield results at the Hartree-Fock limit. For example, this basis set predicts a barrier height for the inversion motion in NH3 which is almost twice as large as the experimental value, while as pointed out before, this same barrier is quantitatively accounted for at the Hartree-Fock limit. The HQ molecule was constrained to... 

The basis set may be constructed from radial functions of either Slater (exponential) or gaussian form, multiplied by appropriate angular (0 and functions. This scheme is frequently referred to by the acronym LCAO-MO -SCF. 

In general, the orbitals in this method are expanded as linear combinations of a basis set of Slater functions in the same spirit as in the LCAO-MO-SCF method. However, in the present case the orbitals are essentially localized, and a description such as equation (67) is clearly equivalent to a linear combination of a great many VB structures, both covalent and ionic. Thus, in the case of methane this should provide a very good description of the ground state, particularly of the potential surfaces for such processes as... 

Semi-empirical calculations for the simple vinyl cation C2H3+ have been reported by Hoffmann (1964) and by Yonezawa et ad., (1968). More rigorous calculations by Sustmann et ad. (1969) are based on a semi-empirical method based on the neglect of diatomic differential overlap (NDDO) calibrated to results of ab initio Hartree-Fock-Roothaan SCF calculations. Recent work by Hopkinson et al. (1971) is entirely based on a non-empirical LCAO-MO-SCF method. 

To date, the best ab initio all-electron molecular calculations involving heavy elements are those of Lee and McLean, who published LCAO-MO SCF relativistic calculations on AgH and AuH (75). They reported relativistic bond-length contractions of 0.08 and 0.25 A, respectively, and increases in... 

The methods under the category of nonempirical fall into two subclasses. The first consists of the well known Hartree-Fock-Roothaan [7, 8] LCAO-MO-SCF (self-consistent field) methods. The second is an even more rigorous... 

Semirigorous LCAO-MO-SCF methods start with the complete many-electron Hamiltonian and make certain approximations for the integrals and for the form of the matrices to be solved. Several years ago, such a method was derived starting with the correct many electron Hamiltonian (in which interelectronic interactions are included explicitly) and the LCAO-MO-SCF equations of Roothaan and then making a consistent series of systematic... 

During the past several years1 there has been an intensive emphasis on calculating such diagrams by nonempirical LCAO-MO-SCF techniques as well as by semiempirical LCAO-MO methods. (Most of these results postdate... 

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