Calculated Mulliken Charges Research Articles

Calculating ESCA core-level binding energies using a PC-based ab initio quantum mechanics program

It is shown that ESCA core-level shifts for organic species may be calculated using a PC-based modelling program package on a routine basis. The sample, ab initio level, calculations discussed only took a few hours each on a Pentium personal computer. This, along with the straightforwardness, enables this type of computation to be performed by the ESCA experimentalist, without the need for expensive or highly dedicated modelling tools. We compare the calculated shifts with experimental and previously reported calculated values, and show that the usual linear relationship between calculated Mulliken charges and the binding energies can also be recovered.

Ab initio molecular orbital calculations of the infrared spectra of hydrogen-bonded complexes of water, ammonia and hydroxylamine. Part 11. The atomic polar tensors, and their invariants, of the monomers and the binary hydrogen-bonded complexes

The atomic polar tensors of the monomers, homodimers and 1:1 binary complexes of water, ammonia and hydroxylamine are reported. These quantities are used to derive the three invariants of each atom in each species, namely the effective charge, the mean dipole derivative and the anisotropy. The trends in the values of these invariants are discussed in relation to the type and strength of hydrogen bond found in each associated species. The invariants, in turn, are used to obtain values for the undeformability parameters and the mass-weighted squared effective charges, and the trends in these quantities are discussed. The results are used in an interpretation of the predicted intensity changes in the infrared spectra of the dimers and complexes, relative to the monomers, reported in a recent series of publications. The intensity changes are also related to the variations of the calculated Mulliken charges of the bonded hydrogen atoms in each hydrogen-bonded environment.

Ab initio molecular orbital study of 1-methylsilatrane and model compounds

Ab initio molecular orbital calculations (3-21G ∗) have been employed to explore bonding in two structures of 1-methylsilatrane: a solid-state structure based upon crystallographic data and a “gas-phase structure” in which the N-Si dative.bond has been artificially lengthened by 0.28 Å. Despite the significant change in N-Si bond strength, there is very little change in calculated Mulliken charges. The utility of the 3-21G ∗ calculations for this system was verified through comparison with 3-21G ∗, 6-31G ∗, other calculational studies and experimental data for NH 3·SiF 4, NH 3·SiF(OH) 3 and a variety of amine-borane adducts.