Second order Moller-Plesset perturbation theory and density functional theory are employed to localize several stationary points on the potential energy surface of the cyclic methanol tetramer. Two cyclic isomers are identified: one of S-4 symmetry, with methyl groups in up-down-up-down configuration, and a second one of C-i symmetry, with the methyl groups in up-up-down-down configuration. The latter minimum is 360 cm(-1) above the S-4 minimum, with a barrier of 475 cm(-1) separating them. These isomers give rise to four asymmetric OH modes around 3300 cm(-1). A model of the concerted proton transfer, S-4-->D-2d-->S-4 (D-2d is the transition structure), yields an estimate of 0.7 cm(-1) for the tunneling splitting of the totally symmetric OH stretch vibrational fundamental. Raman spectra would show evidence of this fundamental and help to identify admixtures of the C-i isomer. (C) 2001 American Institute of Physics.