Two component spin-orbit density functional theory (SODFT) calculations for spectroscopic constants of IX (X = F, Cl, Br and I) molecules have been performed with several functionals using shape-consistent relativistic effective core potentials (RECPs) with effective one-electron spin-orbit operator. The SODFT results obtained with the B3LYP functional are in very good accord with the results of previous two-component CCSD(T) calculations with the same RECP and basis sets. Results of two-component SODFT calculations with RECPs are also in good agreement with reported all-electron relativistic DFT calculations with the same functionals. The spectroscopic constants obtained with ACM and PBE0 functionals display the best agreement with the experimental values among the functionals tested. Spin-orbit effects from the SODFT calculations result in increases of bond lengths and decreases of dissociation energies and harmonic vibrational frequencies and the magnitudes are in reasonable agreement with those from two-component CCSD(T) calculations. Spin-orbit effects appear to be quite insensitive to the choice of functionals for the bond lengths and harmonic vibrational frequencies, but those of the dissociation energies somewhat deviate with the differing class of functionals.