Ab Initio Calculations on Large Molecules Using Molecular Fragments. Hydrocarbon Characterizations

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Abstract
An ab initio procedure for investigation of large molecules is described. The procedure involves two steps, the first of which is the determination of a set of orbitals by the examination of molecular fragments. These molecular fragments and associated orbitals are then combined to form large molecules of interest, using an ordinary LCAO MO SCF‐type procedure. The molecular fragment investigations employed are designed to obtain nonlinear parameters for use in large molecules, and are not used in this study to obtain “small molecules” from which “large molecules” can be formed. Several descriptions of molecular fragments are explored, in which floating spherical Gaussian orbitals are employed, and applications of the method to ethane, propane, ethylene, and benzene are given. Comparisons are made with other methods, and several general characteristics of the method are also discussed.