Nonempirical molecular orbital

S. G. Anderson and D. P. Santry, J. Chem. Phys., 74, 5780 (1981). Nonempirical Molecular Orbital Calculations for Hydrogen-Bonded Molecular Solids Molecular Dipole and Quadruple Moments for Solid Hydrogen Fluoride and Hydrogen Chloride. 

Some references to particularly pertinent molecular-orbital or configuration-interaction calculations of potential curves of diatomic molecules will be mentioned below in this section. These references are not intended to be exhaustive but should serve to indicate some of the calculations which have been carried out and the type of information which is available. (The most comprehensive compilation of nonempirical molecular-orbital calculations is a 1967 survey by Krauss [33], which includes both diatomic and polyatomic molecules.)... 

Fripiat, J. G., P. Galet, J. Delhallo, J. M. Andre, J. B. Nagy, and E. G. Derouane (1985). A nonempirical molecular orbital study of the siting and pairing of aluminium in ferrierite. Phys. Chem. 89, 1932-37. 

Hass, E. C., P. G. Mezey, and P. J. Plath (1981). A nonempirical molecular orbital study on Lowenstein s rule and zeolite composition. J. Molec. Struct. 76, 389-99. 

A nonempirical molecular orbital calculation reported recently for COS by dementi" has indicated, however, that the first excited state is a 7T—IT type. Only s and p type atomic orbitals were used in these calculations. To examine the effect of the 3d orbitals of the sulfur atom on the molecular orbital energy values, an extended Hiickel molecular orbital calculation has also been carried out with and without the inclusion of the 3d orbitals. The resulting energy level diagram for the ground and excited molecular orbitals, in comparison with the atomic... 

Hopkinson, A. C. Nonempirical molecular orbital study of the Wolff rearrangement. J. Chem. Soc., Perkin Trans. 21973, 794-795. 

The minimum potential energy curve of the water dimer is given in Figure 6 for three different water models. Two are effective models, and one is a nonempirical model for comparison. The nonempirical molecular orbital (NEMO) " surface mimics the true two-body water potential V2 in Eq. [44]. It is rather flat, and its minimum is not as sharply defined as in the effective potentials. Pairwise additive potentials like and TIP4P ° show their... 

Parr, R. G., Craig, D. P., and Ross, I. G., J. Chem. Phys. 18, 1561, Molecular orbital calculations of the lower excited electronic levels of benzene, configuration interaction included." One of the most complete nonempirical calculations concerning n electrons. 

Molecular orbital calculations have been performed on compounds 19 and 20 . The calculated PM3 equilibrium geometric structures show that these compounds are severely distorted from planarity in accordance with X-ray structural analysis (see Section 8.I2.3.I). On the other hand, PM3 calculations performed on both neutral and oxidized/reduced compounds show that oxidation and reduction induce a clear gain of aromaticity. Predictions using the nonempirical valence effective Hamiltonian (VEH) method have shown that the electronic charge density in the highest occupied molecular orbital (HOMO) is localized on the benzodithiin 19 or benzoxathiin 20 rings. 

The ground-state wave function of cytosine has been calculated by practically all the semiempirical as well as nonempirical methods. Here, we shall discuss the application of these methods to interpret the experimental quantities that can. be calculated from the molecular orbitals of cytosines and are related to the distribution of electron densities in the molecules. The simplest v-HMO method yielded a great mass of useful information concerning the structure and the properties of biological molecules including cytosines. The reader is referred to the book1 Quantum Biochemistry for the application of this method to interpret the physicochemical properties of biomolecules. Here we will restrict our attention to the results of the v-SCF MO and the all-valence or all-electron treatments of cytosines. 

The ESR spin Hamiltonian parameters have been calculated using 77-HMO and tt-SCF MO coefficients in the molecular orbitals as well as those from nonempirical wavefunctions. It may be seen that, in general, calculated values are in good agreement with experimental data (Table XXXI). 

At the same time, molecular orbitals were used in simplified treatments of the pi-electrons in conjugated organic molecules. Similar empirical or semiempirical electron-structure models were developed and successfully applied in other areas of chemistry. They have been described in other chapters of this book. The field was therefore open for development of a nonempirical HF theory for molecules. A key paper was published by Roothaan in 1951. Albeit not the first to do so, he gave a clear and detailed description of an HF procedure for molecules that could almost be used as a manual for the development of a computer code. The computers were not quite ready, though, and it was to take another 10 years before the first general-purpose codes were produced. 

Th6 theory and the analysis of calculational schemes of quantum chemistry have been dealt with in detail in a number of books [1-6] and review articles [7-12]. Here we give only a brief account of the main principles of the general theory of molecular orbitals (MO) that provides the basis for constructing the most important nonempirical methods of quantum chemistry. 

A. Wallqvist and G. Karlstrbm, Chem. Scripta, 29A, 131 (1989). A New Nonempirical Force Field for Computer Simulations. (This NEMO method of this paper should not be confused with the earlier molecular orbital method with the same name see M. D. Newton, F. P. Boer, and W. N. Lipscomb, /. Am. Chem. Soc, 88, 2353 (1966). Molecular Orbitals for Large Molecules.) C. E. Dykstra, Chem. Rev., 93,2339 (1993). Electrostatic Interaction Potentials in Molecular Force Fields. 

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