We present an algorithm aimed at efficiently representing analytical full dimensional ab initio potential energy surfaces for floppy molecular systems. By introducing a new set of coordinates, we can define large amplitude displacements in one or more dimensions. Then, we use a general representation of the full dimensional potential energy surface based on a Taylor-like series expansion. Classical and quantum mechanical Path Integral Monte Carlo simulations on proton transfer in malonaldehyde and strong hydrogen bond in picolinic acid N-oxide establish the accuracy of our analytical representation and of our interpolating schemes. (c) 2006 Elsevier B.V. All rights reserved.