indicates that permutational invariance of the two H atoms in each monomer. The basis was purified and therefore approaches zero asymptotically. the RMS fitting error is 9.4 cm -1 . Because the correction is short-ranged, we applied a switching function when the OO distance in the dimer is between [6.5, 7.0] Å to make the correction decay to zero; thus the 2-b interaction beyond 7 Å is completely from the TTM3-F force field.