Left: Top and side view of one of the npASW periodic ice models. Cell dimensions are reported in Å. Oxygen atoms are colored according to their altitude. Hydrogen atoms are colored in red if they are dangling OH bond (i.e. non engaged in any HB-bond), else they are colored in white. Right: analog for one of the pASW ice models. All atoms below the 5.2 or 6.1 Å threshold (for npASW and pASW, respectively) are considered bulk and kept frozen at each stages of the work.