Charge Distributions and Chemical Effects. XLI. Alkane Atomic Charges in Energy Calculations.

摘要: Theoretical atomic charges of simple alkanes are examined for their validity in applications to physical problems, namely, calculations atomization energies. A generalization Mulliken’s analysis, allowing an uneven partitioning CH overlap populations, achieves a basis set independent relative ordering charges. This ordering, reflecting the idea that any change electronic structure carbon occurs most reluctantly, is precisely required energy calculations. The absolute magnitude charges, however, dependent. Extensive geometry and scale factor optimizations yield following results (in 10-3 e units) net charge ethane: 69.4 (ST0-3G), 55.1 (ST0-3G + CI), 42.8 (4-31G), 37.8 (4-31G CI). It appears theoretical analyses converge toward empirical result, 35.1 e, provided they carried out after configuration interaction involving reasonably large optimized sets