Cation-pi interaction plays an important role as a general noncovalent binding force in a wide range of systems. To examine the more stable state of carbocation-pi complex, we have carried out Car-Parrinello molecular dynamics (CPMD) simulations of six models. These results are proved to be reliable from the comparison with those of investigations by ab initio calculations. Charge transfer and molecular orbital interaction are discussed to depict the interaction modes of different models. From our CPMD studies without restraints, the methyl group moves toward the side of the benzene forming a stable (Y-complex. However, if the methyl group is maintained above benzene, the inter-conversions among different models of C6H6-CH3+ complex, which are determined from ab initio optimization, are observed; and distances between the carbon of methyl group and the center of benzene range from 2.67 angstrom to 3.61 angstrom. Our results provide a dynamic process concerning the motion of methyl group above the benzene ring. (c) 2006 Elsevier B.V. All rights reserved.