1. Physical and Theoretical Chemistry Laboratory, University of Yaoundé I, P.O. Box 812, Yaoundé, Cameroon
2. Computational Chemistry Laboratory, High Teacher Training College, University of Yaoundé 1, Cameroon. P.O. Box 47, Yaoundé, Cameroon
3. Computational and Theoretical Chemistry Unit, Department of Chemistry, Faculty of Science, University of Douala, P.O. Box 24157, Douala, Cameroon