The gas-phase clustering equilibria of halide ions to a homologous series of alcohol molecules, X- + HOR reversible arrow X-(HOR) (X = F, Cl, Br, I; R = CH3, CH3CH2, (CH3)(2)CH, (CH3)(3)C), have been investigated using ab initio (MP2(full)) and density functional theory (B3LYP) computational methods. For both methods, extended basis sets, including diffuse and polarization functions for all atoms and anions, except I-, were used. For I- three different effective core potentials (ECP) were used to test their suitability for these systems. Comparing the Delta H(298)degrees and Delta S(298)degrees values obtained with various experimental data indicates that the MP2 and MP2//B3LYP methods perform best. Structural and spectroscopic features, as well as charge distributions, show interesting trends for the various X-(HOR) complexes, and the intrinsic contributions of the halide ions and the alcohol molecules to these trends are discussed. Finally, two-dimensional potential energy surface scans were performed for the X-(HOCH3) complexes at the MP2/6-311++G(d,p) level of theory. These surfaces reveal the asymmetric nature of the potential energy surface for the heavier halide ions, and the "floppy" nature of all the halide ion adducts.