A quantum mechanical study on the electrostatic interactions of mixed surfactant systems was performed, 15 reduced complexes were considered in the gas phase, chloroform solution, and aqueous solution. The geometries were fully optimized in gas phase at the MP2/6-31G(d) level, single points calculations were performed for all the complexes and monomers at the HF/6-31G(d), HF/6-311G(d,p), HF/6-311++G(d,p), MP2/6-31G(d), MP2/6-311G(d,p), and MP2/6-311++G(d,p) levels of theory. The influence of solvent was investigated at the MP2/6-311++G(d,p) level using the polarizable continuum model. (c) 2004 Elsevier B.V. All rights reserved.