Abstract :
A new method for the calculation of similarities between atoms in molecules is presented. This new method is based on the first-order atomic polar tensors (APT), that is, the derivatives of the dipole moment with respect to the Cartesian coordinates of the atoms to be compared. A new concept, the direction depending charge of an atom, appears as a key step in the derivation of the method. With this charge function one can easily obtain the expression of the already defined generalized APT charges. Similarity results obtained with the APT method appear to be qualitatively and semiquantitatively comparable with previous results obtained with methods involving the density function. This new method has the advantage of being faster than the density-based methods which require numerical integration. Also it appears to be almost independent of the level of calculation.
