Assessment of binding energies of atmospherically relevant clusters

This work assesses the binding energies of atmospherically relevant clusters containing H2SO4, H2O, NH3 and (CH3)(2)NH using density functional theory. The performance of seven DFT functionals (B3LYP, CAM-B3LYP, M06-2X, PW91, LC-PW91, PBEO and omega B97X-D) is evaluated against high level explicitly correlated coupled cluster methods using a test set of 107 atmospherically relevant clusters. Our studies show that all the tested functionals correlate well with the coupled cluster results, but with highly varying mean absolute errors. The PBE0, CAM-B3LYP, PW91 and M06-2X functionals are found to perform similarly with errors in the range of 2.53-3.46 kcal mol(-1), while the B3LYP and LC-PW91 functionals yield higher errors of 6.95 kcal mol(-1) and 10.66 kcal mol(-1), respectively. The omega B97X-D functional gives the best estimate of the binding energies with a mean absolute error as low as 2.12 kcal mol(-1) over the large test set of clusters.