Thermal conductivity in amorphous ices from molecular dynamics

Abstract

The observed unusual thermal conductivities of low-, high- and very high-density amorphous ices ($a$-ices, LDA, HDA, and VHDA) are reproduced by equilibrium molecular-dynamics calculations with the Green-Kubo approach. The fast and slow relaxation times of the heat flux correlation functions were found to be dependent on, respectively, the short- and intermediate-range structural ordering. In conjunction with the collective nature of the acoustic vibrations, it can be concluded that the short and intermediate ordering of $a$-ices is similar to collapsed ice rather than a liquid. The larger phonon linewidths in HDA and VHDA vis-\`a-vis LDA are a clear indication of hybridization between acoustic and optic phonon branches resulting in an increase in decay channels in the dense amorphous states and shorter phonon mean-free paths.