While being considered as the building block of ice on a hydrophobic metal surface, the global minimum of the water hexamer is still elusive, which has impeded our understanding of water/metal interfaces. Herein, we comprehensively investigate water hexamer on Cu(111) theoretically and propose the boat configuration as the new in situ adsorption configuration from the scanning tunneling microscope experiments. All existing experimental measurements can therefore be well reproduced. Calculations in high-level theories reveal that the boat configuration is indeed the global minimum under experimental conditions, solving a longstanding discrepancy.
