The imperfect agreement between MP2 simulations and the experimental structure may be attributed to an insufficient basis set. Calculations are carried out using a triple-ζ basis set. MP2 is known to overestimate dispersion when a relatively small basis set is applied. Previous studies indicate that as the basis set increases from double-ζ to triple-ζ to quadruple-ζ , the mean absolute error in the binding energies relative to the complete basis set (CBS) values decreases from 2.18 to 1.74 to 0.99 kcal/mol for the water clusters (n=2-10). The relatively small basis set overestimates the binding energies compared to the CBS. The global minima of water clusters (n=2-6) at the MP2 level agree with the CCSD(T) level of theory. However, MP2 systematically contracts the nearest-neighbor O-O separation in water clusters by 0.005 -0.022 Å with the average of 0.016 Å. In this respect, MP2 tends to overestimate binding energies compared to CCSD(T) results at the same quality of basis set (aug-cc-pVDZ). When the binding energies are extrapolated to the CBS limit, both MP2 and CCSD(T) predict very similar values. The differences between the two methods are generally lower than 0.5 kcal/mol. Given the fact MP2 with triple-ζ overbinds and overestimates the dispersion, it is not surprising that MP2 water at room temperature over-structures and behaves like ice. The temperature dependence of the RDFs as shown in Fig. from 240 to 350 K was also examined. The RDFs are strongly affected by the temperature with a negative correlation at each peak. Temperature effects are more pronounced at the first peaks of g OO (r) which concerns the structure of the first solvation shell. As the temperature increases, the water becomes less ordered with a relatively lower intensity of g OO (r) at the first peak. NQEs broaden and weaken the intensity of the first peaks in g OO (r) and these effects are more pronounced at a lower temperature. A temperature difference of ∼ 30 K in classical simulations is required to give the same height of g OO (r) as in quantum simulations, indicating that the quantum simulation is "hotter". Indeed, classical MD simu- lations of water are often carried out at an elevated temperature to mimic the quantum effect of oxygen and yield an improved description of the local structure of water. In fact, NQEs are more significant when light atoms are involved. This simulation protocol with an artificial elevation of 30 K may fail dramatically in describing the g HH (r) and g OH (r). As shown in Fig. ), NQEs significantly broaden the first and second peaks of g HH (r) and g OH (r). Similarly, we also plot the temperature dependence of the height of the second peaks of g HH (r) and g OH (r). It is evident that the temperature difference may be more than 70 K for g HH (r) (See subplots in Fig. )) and 50 K for g OH (See subplots in Fig. )) at the second peak of the RDFs. More importantly, the broadening of the first peaks of g HH (r) and g OH (r) cannot be reproduced with an elevated temperature even up to 70 K. Classical MD simulations only sample within the range of the thermal energy kT , which is far below the zero-point energy of an O-H stretch. Accurate RDFs can be achieved from MP2 theory with a higher temperature of 340 K, as shown by our classical and quantum dynamics. As in Fig. , the experimental RDFs at room temperature are given in the dashed black lines. The calculated g OO (r), g HH (r) and g OH (r) at 340 K match with the experimental value at room temperature. To further understand the local structure of the water molecules, we calculate the distribution oxygen-oxygen-oxygen triplet angles within the first solvation shell and the tetrahedral order parameter q, defined as