Ice Ih

Ice Ih (hexagonal ice) is a proton disordered ice phase having the space group P6₃/mmc. Ice Ih has the following lattice parameters at 250 K: a=4.51842 Å, $b=a{\sqrt {3}}$ , and c=7.35556 Å with four molecules per unit cell (in Table 3 of ^[1]). The proton ordered form of ice Ih is known as ice XI, which (in principle) forms when ice Ih is cooled to below 72K (it is usually doped with KOH to aid the transition).

Melting point

The following is a collection of melting points $(T_{m})$ for the ice Ih-water transition (experimental value is 273.15 K at 1 bar):

$T_{m}$	Pressure	Water model/technique	Reference
$190~K$	1 bar	SPC	^[2]
$215(4)~K$	1 bar	SPC/E / free energy calculation	^[3]
$146~K$	1 bar	TIP3P	^[2]
$232(4)~K$	1 bar	TIP4P / free energy calculation	^[3]
$272(6)~K$	1 bar	TIP4P/Ice / free energy calculation	^[3]
$245.5(6)~K$	1 bar	TIP4P/Ew / free energy calculation	^[3]
$252(6)~K$	1 bar	TIP4P/2005 / free energy calculation	^[3]
$274~K$	1 bar	TIP5P	^[2]
$289~K$	1 bar	NvdE	^[4]
$417\pm 3~K$	2500 bar	Perdew-Burke-Ernzerhof functional	^[5]
$411\pm 4~K$	10,000 bar	Becke-Lee-Yang-Parr functional	^[5]
$242.65\pm 1.5~K$	1 bar	TTM2.1-F (classical)	^[6]
$227.65\pm 1.5~K$	1 bar	TTM2.1-F (quantum)	^[6]