VARIABILITY OF SHAPES AND PROPERTIES OF ATOMS IN MOLECULES - A CASE-STUDY OF THE CARBONYL OXYGEN

A comparative study of carbonyl oxygen atoms in diverse molecular envi ronments is presented. The variability of shapes of oxygen atoms is qu antified with a newly developed similarity measure that confirms the q ualitative conclusions of visual assessment. Electronic properties of these atoms, such as charges, energies, and dipole moments, are comput ed and their possible correlations with the atomic shapes are studied. Factors that affect atomic shapes are investigated and found to be di stinct from those influencing electronic properties of atoms in molecu les. The kinetic energies of the atoms under study correlate poorly wi th the atomic charges. The second-neighbor effects on the atomic energ ies and charges are approximately additive. Both the theoretical consi derations and the numerical results definitively rule out the possibil ity of the shapes of atomic basins unambiguously determining the prope rties of atoms in molecules. The consequences of this observation for the recently contemplated approaches to the prediction of electronic p roperties of large molecules are discussed.