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Self-Consistent Molecular-Orbital Methods. IX. An Extended Gaussian-Type Basis for Molecular-Orbital Studies of Organic Molecules

1971/01/15 by R. Ditchfield, Warren J. Hehre, W. J. Hehre +2 · 10,603 citations
Chemistry · Mathematics · #Analytical Chemistry and Chromatography #Atomic physics #Basis function #Basis set #Chemical Thermodynamics and Molecular Structure #Chemistry #Computational chemistry #Density functional theory #Fragment molecular orbital #Gaussian #Geometry #Group (periodic table) #Hydrogen atom #Mathematics #Molecular orbital #Molecular orbital theory #Molecular physics #Molecule #Non-bonding orbital #Physics #Polyatomic ion #Quantum mechanics #STO-nG basis sets #Scaling #Valence (chemistry) #Various Chemistry Research Topics

paper · doi:10.1063/1.1674902

published in The Journal of Chemical Physics 54(2), 724-728 (American Institute of Physics)

openalex publication_date 1971/01/15 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05

Abstract

An extended basis set of atomic functions expressed as fixed linear combinations of Gaussian functions is presented for hydrogen and the first-row atoms carbon to fluorine. In this set, described as 4–31 G, each inner shell is represented by a single basis function taken as a sum of four Gaussians and each valence orbital is split into inner and outer parts described by three and one Gaussian function, respectively. The expansion coefficients and Gaussian exponents are determined by minimizing the total calculated energy of the atomic ground state. This basis set is then used in single-determinant molecular-orbital studies of a group of small polyatomic molecules. Optimization of valence-shell scaling factors shows that considerable rescaling of atomic functions occurs in molecules, the largest effects being observed for hydrogen and carbon. However, the range of optimum scale factors for each atom is small enough to allow the selection of a standard molecular set. The use of this standard basis gives theoretical equilibrium geometries in reasonable agreement with experiment.

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