A continuum of amorphous ices between low-density and high-density amorphous ice

Ali Eltareb; Gustavo E Lopez; Nicolas Giovambattista

doi:10.1038/s42004-024-01117-2

A continuum of amorphous ices between low-density and high-density amorphous ice

Commun Chem. 2024 Feb 20;7(1):36. doi: 10.1038/s42004-024-01117-2.

Authors

Ali Eltareb^{1

2}, Gustavo E Lopez^{3

4}, Nicolas Giovambattista^{5

6

7}

Affiliations

¹ Department of Physics, Brooklyn College of the City University of New York, Brooklyn, NY, 11210, USA. ali.eltareb@brooklyn.cuny.edu.
² Ph.D. Program in Physics, The Graduate Center of the City University of New York, New York, NY, 10016, USA. ali.eltareb@brooklyn.cuny.edu.
³ Department of Chemistry, Lehman College of the City University of New York, Bronx, NY, 10468, USA. gustavo.lopez1@lehman.cuny.edu.
⁴ Ph.D. Program in Chemistry, The Graduate Center of the City University of New York, New York, NY, 10016, USA. gustavo.lopez1@lehman.cuny.edu.
⁵ Department of Physics, Brooklyn College of the City University of New York, Brooklyn, NY, 11210, USA. ngiovambattista@brooklyn.cuny.edu.
⁶ Ph.D. Program in Physics, The Graduate Center of the City University of New York, New York, NY, 10016, USA. ngiovambattista@brooklyn.cuny.edu.
⁷ Ph.D. Program in Chemistry, The Graduate Center of the City University of New York, New York, NY, 10016, USA. ngiovambattista@brooklyn.cuny.edu.

Abstract

Amorphous ices are usually classified as belonging to low-density or high-density amorphous ice (LDA and HDA) with densities ρ_LDA ≈ 0.94 g/cm³ and ρ_HDA ≈ 1.15-1.17 g/cm³. However, a recent experiment crushing hexagonal ice (ball-milling) produced a medium-density amorphous ice (MDA, ρ_MDA ≈ 1.06 g/cm³) adding complexity to our understanding of amorphous ice and the phase diagram of supercooled water. Motivated by the discovery of MDA, we perform computer simulations where amorphous ices are produced by isobaric cooling and isothermal compression/decompression. Our results show that, depending on the pressure employed, isobaric cooling can generate a continuum of amorphous ices with densities that expand in between those of LDA and HDA (briefly, intermediate amorphous ices, IA). In particular, the IA generated at P ≈ 125 MPa has a remarkably similar density and average structure as MDA, implying that MDA is not unique. Using the potential energy landscape formalism, we provide an intuitive qualitative understanding of the nature of LDA, HDA, and the IA generated at different pressures. In this view, LDA and HDA occupy specific and well-separated regions of the PEL; the IA prepared at P = 125 MPa is located in the intermediate region of the PEL that separates LDA and HDA.