The hypervalent PF4H species dimer has been studied using second-order perturbation theory and coupled-cluster methods with augmented correlation-consistent basis sets up to truncated quadruple-zeta. The dimer involving two P-H-... F contacts serves a model of weak interaction between PF4H molecules in the crystal. We found dimer structures of C-I and C-i symmetry with interaction energy of the order of -2.5 kcal/mol. SAPT (symmetry-adapted perturbation theory) energy decomposition scheme reveals major electrostatic, polarization and dispersion stabilizing contributions. We are not conclusive as to the presence of improper H-bonding in this complex. (c) 2005 Elsevier B.V. All rights reserved.