Ab initio calculations on large molecules using molecular fragments First order electronic properties for hydrocarbons

A number of first order electronic properties for the hydrocarbons C₂H₆, C₃H₈, C₂H₄, C₆H₆, and C₁₀H₈ are investigated. The wavefunctions employed here result from SCF calculations, using basis orbitals that have been optimized in molecular fragment studies. Comparisons are made with experimental values as well as with other calculated values, and the suitability of various molecular fragment bases is discussed.     

Quadratically convergent iteration procedure for geminal determinations

A general formalism is presented for the determination of the optimum natural orbitals within the various strongly orthogonal geminals of a wavefunction describing a 2N-electron closed-shell molecule or atom. The relationship to Hartree–Fock–Roothaan theory is established; the algorithm that is developed is quadratically convergent to the desired result, and does not ignore off diagonal Lagrangian multipliers, or require an infinite series of 2 × 2 orthogonal transformations of the original basis.