Molecular dynamics study of ice structural evolution

Molecular dynamics simulation is employed to study the structural evolution of low density amorphous ice during its compression from one atmosphere to 2.5\,GPa. Calculated results show that high density amorphous ice is formed at an intermediate pressure of $\sim $1.0\,GPa; the O--O--O bond angle ranges from 83$^{\circ}$ to 113$^{\circ}$, and the O--H$\cdots$O bond is bent from 112$^{\circ}$ to 160$^{\circ}$. Very high density amorphous ice is obtained by quenching to 80\,K and decompressing the ice to ambient pressure from 160\,K/1.3\,GPa or 160\,K/1.7\,GPa; and the next-nearest O--O length is found to be 0.310\,nm, just 0.035\,nm beyond the nearest O--O distance of 0.275\,nm.