Table I: Structural Data on the Phases of Ice

Ice phase	Crystal system	Space group	Cell dimensionsa (pm, deg)	No. of molecules in a unit cell	No. of nearest neighbors	Distance of nearest neighbors (pm)	O···O···O anglesa (deg)	Hydrogen positions	Densitya (Mg m-3
Ih	Hexagonal	P63/mmc	a=450; c=732	4	4	275	109.3, 109.6	Disordered	0.93
Ic	Cubic	Fd3m	a=635	8	4	275	109.6	Disordered	0.94
aI	Amorphous	-	-	-	4	277	-	Disordered	1.17
aII	Amorphous	-	-	-	4	280	-	Disordered	1.17
II	Rhombohedral	R3	a=778; =113.1	12	4	275-284	80-128	Ordered	1.18
III	Tetragonal	P41212	a=673; c=683	4	4	276-280	87-141	Disordered	1.15
IV	Rhombohedral	R3c	a=760; =70.1	16	4	279-292	87.7-127.8	Disordered	1.27
V	Monoclinic	A2/a	a=922; b=754 c=1035; =109.2	28	4	276-287	84-128	Disordered	1.24
VI	Tetragonal	P42/nmc	a=627; c=579	4	4	280-282	76-128	Disordered	1.33
VII	Cubic	Pn3m	a=341	2	8	295	109.5	Disordered	1.56
VIII	Tetragonal	I41amd	a=480; c=699	8	8	296 and 280d	109.3, 109.5	Ordered	1.56
IX	Tetragonal	P412121	a=673; c=683	12	4	276-280	87-140	Ordered	1.16
X	Cubic	Pn3m	a=283	2	8	245	109.5	Symmetric	2.51

^aCell dimension and density are at 110 K and atmospheric pressure. Ice X at 44 GPa and 25šC.

^bBecomes partially ordered when quenched to low temperatures. A more fully ordered phase V' has space group P2₁/a.

^cWhen cooled slowly to - 150šC, ice VI' is partly ordered with orthorhombic space group Pmmn. A fully ordered ice VI" has space group Pn.

^dFour of the nearest neighbors are hydrogen-bonded to central molecule at a distance of 296 pm; four are non-bonded at 280 pm.