Comparison of the performance of local, gradient-corrected, and hybrid density functional models in predicting infrared intensities

Density functional theory has been used to calculate infrared (IR) intensit ies for a series of molecules (KF, CO, H2O, HCN, CO2, C2H2, H2CO, NH3, C2H4 , CH2F2, CH2Cl2, and CH2Br2) in an effort to evaluate relative performance of different functionals. The methods employed in this study comprise most of the popular local, gradient-corrected, and hybrid functionals, namely, S -VWN, S-PL, B-LYP, B-P86, B-PW91, B3-LYP, B3-P86, and B3-PW91. Calculations were carried out using various qualities of split valence basis sets augme nted with diffuse and polarization functions, both to determine basis set d ependence and to evaluate the limit performance. Computed intensities were compared with results from conventional correlated ab initio methods (MP2 a nd QCISD). Hybrid functionals give results in closest agreement with QCISD over the other methods surveyed. Local and gradient-corrected methods perfo rmed remarkably alike, both are comparable to MP2, and outperform Hartree-F ock. Hartree-Fock intensities can be dramatically improved by scaling, maki ng them similar to MP2 results. (C) 1998 American Institute of Physics. [S0 021-9606(98)30748-5].