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 environments is presented. The variability of shapes of oxygen atoms is quantified with a newly developed similarity measure that confirms the qualitative conclusions of visual assessment. Electronic properties of these atoms, such as charges, energies, and dipole moments, are computed and their possible correlations with the atomic shapes are studied. Factors that affect atomic shapes are investigated and found to be distinct from those influencing electronic properties of atoms in molecules. The kinetic energies of the atoms under study correlate poorly with the atomic charges. The second-neighbor effects on the atomic energies and charges are approximately additive. Both the theoretical considerations and the numerical results definitively rule out the possibility of the shapes of atomic basins unambiguously determining the properties of atoms in molecules. The consequences of this observation for the recently contemplated approaches to the prediction of electronic properties of large molecules are discussed. Key words: atoms in molecules, properties of —; similarity of —; transferability of —.