This analysis is presented graphically in Fig. which also shows results from TTM3-F. The results shown there and in the Table are even more accurate those from our q-AQUA potential, which is truncated at the 4-b level 10 and also more accurate than the MB-pol potential. Figure shows the deviations in the harmonic frequencies of various water potential on 4 hexamer isomers, compared to the benchmark calculations. The TTM3-F model significantly underestimates the frequencies of OH stretches, as seen in the figure. Both MBpol and q-AQUA are quite accurate, and can achieve a mean absolute deviation of ∼ 10 cm -1 .