The average water-surface distance, d(W-Fe1), of H-down has the shortest of 2.92 Å, indicating stronger interaction with the surface. The results are supported by several previous studies on metals such as Pt and Au surfaces which have also demonstrated that H-down water configurations are more stable. The next shortest is the H-mix of 3.12 Å and the longest is H-up of 3.31 Å. The interlayer distances between Fe(100) layers vary depending on the specific atomic layers and the orientations of the water molecules. The distance between bare Fe(100) layers 1 and 2 (d(Fe1-Fe2)) is 1.36 Å, which is shorter than the 1.46 Å distance between layers 2 and 3 (d(Fe2-Fe3)). Placing water molecules on the Fe(100) surface impacts these distances. For example, water molecules reduce the distances between all Fe(100) layers for all water orientations, except for the d(Fe1-Fe2) distances in the H-down and H-mix configurations, which are elongated to 1.41 Å and 1.37 Å, respectively. This elongation can be attributed to relatively strong interactions between the water molecules and Fe(100) surface in these configurations, causing a slight shift of the top Fe atomic layer towards the electrolyte.