The (3-D) crystal structur o H2O ice Ih (c) consists o bases o H2O ice molecules (b) locatit on lattice pynts within the (2-D) hexagonal space lattice (a). The valyies for the H–O–H angle an O–H distance hae come frae Physics of Ice[1] wi uncertainties o ±1.5° an ±0.005 Å, respectively. The white box in (c) is the unit cell defined bi Bernal an Fowler[2]