Ferreira M. M. C., “Population Analysis from Atomic Polar Tensors?”. Vienna, Austria, 23-28/08/1992: XXIst European Congress on Molecular
Spectroscopy (EUCMOS XXI), Abstracts, 138 (1992). Poster D 6.38.

D 6.38 POPULATION ANALYSIS FROM ATOMIC POLAR TENSORS?

Márcia M. C. Ferreira

Instituto de Química, Universidade Estadual de Campinas,
Campinas, S.P. 13081 Brazil

The dipole moment derivatives with respect to the atomic cartesian displacements
give origin to two tensors (represented as 3 x 3 matrices), called charge and
charge tensors. The sum of these two tensors is the well known Atomic Polar Tensor,
which is experimentally obtained from infrarred intensities of molecules in its gas
phase.
Since the charge tensor is not diagonal, the atomic charge is defined as 1/3 of its
trace [ref. 1]. This atomic charge is invariant under rotation of the coordinate
system and that makes it a physically intrinsic quantity which is not the case for
the Atomic Polar Tensor.
The atomic charges for hydrogen, carbon, nitrogen, oxygen and fluorine atoms are
calculated by the ab-initio method using 4-31G basis set, for a series of fifteen
molecules. The results obtained in this work are compared to other experimentally
and theoretical atomic charges which are given in the literature.
The calculated Atomic Polar Tensors are in good agreement with the values experi-
mentally obtained.
A test with water and ammonia molecules shows that the defined atomic charge is
almost invariant with respect to the basis set, contrary to the Mulliken's net
atomic charge which are well known to be strongly basis set dependent.
The obtained atomic charges show a linear relationship with the electronegativities
of characteristic groups in similar molecules.

[ref. 1] Márcia M. C. Ferreira and Elisabete Suto submitted for publication.

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