LCAO-MO-SCF calculations

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). ... 

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. 

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. 

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 intermediate of the 0+ + N2 reaction, N20+, has 15 valence electrons, and thus it is assumed to have a linear configuration (N-N-0+) in accordance with Walsh s rules [97] for a 15 valence electron triatomic. Experimentally the ground state of N20+ is known to be 2n, and its first excited state, lying at 3.45 eV, to be 2 + [174], A second excited state with no symmetry assigned had been reported at 7.19 eV [6]. McLean and Yoshimine at IBM had done accurate LCAO-MO-SCF calculations on the parent system N20 itself [57]. The bond lengths of ground state N20+ and N20 are quite similar [174],... 

Certainly detailed theoretical treatments of the stabilities, energetics, and electronic states of the doubly-charged negative ions, both monatomic and polyatomic, are now warranted. It was noted eariier that the EHT calculations employed here are only a zerot/i order approximation the results obtained, however, now justify an effort to employ more sophisticated approaches. The MINDO and LCAO-MO-SCF calculations mentioned above are a distinct improvement over the EHT calculations. Other calculational techniques should be brought to bear on an improved understanding of doubly-charged negative ions. 

There have been several contributions that have focused on the nature and energetics of the electronically excited states of OCS. An LCAO-MO-SCF calculation by Clement (105) showed that the first excited states above the ground state arise from a 37r 4ir (II-II ) configuration from which six singlet and triplet sigma and delta states can be derived, the lowest being The very low f-value for the near ultraviolet transition suggests that the upper bound state of this transition is A. 

Ab initio LCAO-MO-SCF calculations on the same species have given values for the electric field gradients, electric fields, diamagnetic shieldings, dipole moment, second moment, and diamagnetic susceptibility.155... 

Ab-Initio LCAO-MO-SCF Calculations of the Electrostatic Molecular Potential of Chlorpromazine and Promazine,"... 

Nonempirical LCAO-MO-SCF calculations on a heuristic model system ) have led to the same conclusions as the arguments summarized above. In addition, these same calculations revealed previously unsuspected features of the reaction system, namely, the conditions under which the star-point barrier (45) is surmountable, since it appeared that the relief of stereo-electronic strain afforded when both relatively electronegative ligands occupy a positions (as in 45) all but compensates for ring strain. The following experimental results are in agreement with this prediction. 

Petrongolo C, Preston HJT, Kaufman JJ. Ab nitio LCAO-MO-SCF calculation of the electrostatic molecular potential of chlorpromazine and promazone. Int J Quantum Chem 1978 13 457-468. 

Ab Initio LCAO-MO SCF calculations have been used to elucidate the electronic structure of the molecules H S, HtSO, H2SOt, with and without d orbitals being allowed to the sulfur. Three-dimensional plots of the various molecular orbitals are presented and discussed. 

The ab initio LCAO-MO-SCF calculations were carried out with the program MOSES (4), and the electron densities were calculated by another program (an electron-density program modified by T. H. Dunning at the California Institute of Technology and later improved by H. Mars-mann and I. Absar) (8), the results from which were converted into computer-made three-dimensional plots by yet another program (9). 

Beryllium halides and pseudohalides have been reviewed. Non-empirical LCAO MO SCF calculations are reported for the ground, C2 states of the Group II dihalides BeF2, MgF2, and CaF2. The calculations demonstrate the importance of id orbitals in the bonding of the dihalides and hence in the... 

LCAO-MO-SCF calculations have been carried out for a number of covalent B—polymers. These include (HB=NH) , (BHg— NH2) , and the B- and iV-chloro-analogues. Calculated bond structures were compared with results for the isoelectronic carbon systems. 

Early theoretical work by Dedieu and coworkers focused on individual elementary transition metal (TM) reactions for the hydrogenation of ethylene using a model of Wilkinson s catalyst [RhCl(PPH3)3] [3-6]. They used LCAO-MO-SCF calculations to perform an orbital analysis of the oxidative addition step, determine intermediate stability, and analyze the olefin insertion step. Using SCF calculations and orbital correlation diagrams for the valence orbitals of the reactants and products, they analyzed the feasibility and geometry of the oxidative addition shown in (1). 

A LCAO-MO-SCF calculation of equation (45) suggests that the reaction is best described as olefin insertion and not hydride migration. Good TT-donor ligands are predicted to promote the reaction. 

Some more rigorous, non-parametric calculations also confirm the validity of the isolobal principle. Fenske-Hall LCAO-MO-SCF calculations of the structure of B5H9 and some of its ferroborane derivatives, i.e. l-Fe(CO)3B4Hs, 2-Fe(CO)3B4Hs and l,2-[Fe(CO)3]2B3H3 have been completed. A summary of a qualitative description of the properties of frontier molecular orbitals in... 

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