“Supercooled water and amorphous states”

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Supercooled water and amorphous states
Fausto Martelli
IBM Research
Water is arguably the most important material in our life. It is indeed one of the most studied
materials, but it is also one of the least understood. It shows a remarkable number (72) of
anomalies and a very rich phase diagram.In this talk, I will look at the properties of water from the
perspective of the hydrogen bond network (HBN) in supercooled liquid water, and in glassy water.
Supercooled liquid water I have simulated, via classical molecular dynamics simulations, the
isobaric cooling of liquid water from ambient temperature to 190K at different pressures, crossing
the Widom line at each pressure. I will show that peculiar arrangements of the HBN in supercooled
water occur in correspondence with the Widom line [1]. In particular, in correspondence with the
Widom line the HBN connecting locally ordered environments acquires maximal frustration
between a configuration that promotes crystallisation and a configuration that promotes fluidising
tendencies [1].
Amorphous water At deeply supercooled conditions, water exhibits polyamorphism, i.e., it exists
in more than one amorphous solid state. The most common forms of glassy water are the lowdensity
(LDA) and the high-density amorphous (HDA) ice. I have simulated the formation of LDA
upon rapid quenching of liquid water at 1 atm from 300 K to 80 K, and I have simulated the
isothermal compression of LDA to produce HDA. I will show that the HBN of both LDA and HDA
can be considered as hyperuniform networks, i.e., continuous random networks endowed with the
capability (typical of crystalline solids) of suppressing large-scale density fluctuations, while
hyperuniformity is lost in correspondence with the first-order-like LDA-to-HDA phase transition
[2,3]. I will then discuss the connection between local order and hyperuniform networks in
amorphous ices [4].
[1] F. Martelli “Unravelling the contribution of local structures to the anomalies of water: The
synergistic action of several factors”, J. Chem. Phys. 150, 094506 (2019)
[2] F. Martelli, S. Torquato, N. Giovambattista, R. Car “Large-Scale Structure and Hyperuniformity
in Amorphous Ices”, Phys. Rev. Lett., 119, 136002 (2017)
[3] F. Martelli, N. Giovambattista, S. Torquato, R. Car “Searching for crystal-ice domains in
amorphous ices”, Phys. Rev. Mater., 2, 075601 (2018)
[4] F. Martelli, S. Torquato, N. Giovambattista, R. Car “Hyperuniformity and local structures in
amorphous ices”, J. Chem. Phys. Accepted