As illustrated in Fig. , GGA functionals tend to underestimate the equilibrium density, which is rectified by adding dispersion corrections. The incorrect prediction that ice sinks in water with local DFT is mainly due to the absence of dispersion in plain GGA functionals . However, meta-GGA functionals such as SCAN have been shown to correct this issue . The PBE0 hybrid functional faces challenges in achieving the right balance between covalent, hydrogen bonds and vdW forces. It significantly underestimates the density, but this can be improved with the D3 correction. For all other meta-GGAs, hybrids, hybrid meta-GGAs and rung-5/post-HF, the density is higher than the experimental value. Overall, vdW interactions increase the density because of their attractive and isotropic nature at intermediate and long range. This increases the population of molecules in the intershell regions of the O-O distribution function, i.e. between the coordination shells, and acts as additional cohesive force in the condensed phase. Consistent with their structural differences (Fig. ), the increase in the amount of exact exchange in the M06, M06-2X and M06-HF also correlates with a rise of the density. On the other hand, in a counteracting manner, the delocalization and disordering effects due to NQEs can be expected to reduce the density, explaining why DFT densities with classical nuclei are usually overestimated.