A working methodology to generate theoretical IR spectra following ab initio electronic structure methods is reported. Theoretical IR spectra of Cl-2(center dot-)center dot nH(2)O clusters (n = 1-5) are generated as a case study. Excellent agreement between the calculated and the reported experimental IR spectra based on size-selected spectroscopy is observed. It is shown that uniform scaling of calculated harmonic frequencies of these hydrated dusters fail to produce accurate IR spectra. Two different scaling factors in two different regions of O-H stretching of solvent water molecules are needed to account for the anharmonic contribution. This observation is also true for Br-2(center dot-)center dot nH(2)O and I-2(center dot-)center dot nH(2)O systems.