Structure of water adsorbed on the open Cu(1Â 1Â 0) surface: H-up, H-down, or both?

Water adsorbs molecularly in a 2:1 ratio of H-down and H-up configurations on Cu(1 1 0). This open surface provides a range of adsorption sites and competing interactions causing this structure to deviate from the general picture of water adsorbed on close-packed (1 1 1) surfaces where water adsorbs primarily H-down.