arXiv:1002.4118v1 [cond-mat.soft] 22 Feb 2010 1 Classical-path integral adaptive resolution in molecular simulation: towards a smooth quantum-classical coupling Abstract Simulations that couple different classical molecular models in an adaptive way by changing the number of degrees of freedom on the fly, are available within reasonably consistent theoretical frameworks. The same does not occur when it comes to classical-quantum adaptivity. The main reason for this is the difficulty in describing a continuous transition between the two different kind of physical principles: probabilistic for the quantum and deterministic for the classical. Here we report the basic principles of an algorithm that allows for a continuous and smooth transition by employing the path integral description of atoms. PACS numbers: 02.70.Ns, 61.20.Ja, 61.25.Em A.B.Poma and L.Delle Site Max-Planck-Institute for Polymer Research, Ackermannweg 10, D 55021 Mainz Germany.