Electronegativity Equalization Method – Fast Method For Charge Calculation

Z. Jiroušková¹, R. Svobodová Vařeková¹, J. Vaněk¹, J. Koča¹

¹National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno

xjirousk@chemi.muni.cz

The progress which appeared in the latest decades in the computational field established computational chemistry methods to be of comparable quality to experimental methods. The number of cases in which computational chemistry methods can be successfully applied is still increasing and these methods are nowadays used with profit for modeling molecular systems and detailed studies of various structural and functional properties.

Partial atomic charge is a molecular property which is very often used in chemistry, particularly for clarification of differences in structure or reactivity between molecules. Unfortunately, partial charges are not obtainable from experiment, but they can be derived using the quantum chemistry methods. In the quantum chemistry, there are more approaches, how to solve this task, but none of them can be considered to be the best one and what is more, these methods are on one hand very precise, but also quite time-demanding. For some types of calculations it is not acceptable to wait for the results for such long time and for that reasons also some alternative approaches appeared. These approaches are based mostly on the semi-empirical principles and the Electronegativity Equalization Method is one of them.

The Electronegativity Equalization Method was developed as a semi-empirical method based on the Density Functional Theory [1] and it is a fast way how to obtain appropriate partial charges for arbitrary molecule. The methodology is based on the Sanderson’s Electronegativity Equalization Principle [2] which is applied to the Density Functional Theory. Due to its semi-empirical character, it is necessary to parameterize the Electronegativity Equalization Method before the first usage and the parameterization process influences the quality of resulting charges. We have already parameterized the Electronegativity Equalization Method on very large sets of organic, organohalogen and organometal molecules from the Cambridge database of crystallographic structures (CSD) and the National Cancer Institute 3D structure database (NCI DIS). Based on these training sets, very robust parameterization was performed and the number of so far parameterized elements was increased [3, 4]. The obtained parameters were carefully validated and resulting partial atomic charges were in a very good agreement with quantum mechanically calculated partial atomic charges.

1. R. G. Parr, W. Yang, Density-Functional Theory of Atoms and Molecules, Oxford University Press, (1989)

2. R. T. Sanderson, J Am Chem Soc, 105, (1983), 2259.

3. R. Svobodová Vařeková, Z. Jiroušková, J. Vaněk, Š. Suchomel, J. Koča, Int. J. Mol. Sci., 8, (2007), 572.

4. Z. Jiroušková, R. Svobodová Vařeková, J. Vaněk, J. Koča, J Comput Chem, electronically published ahead of print