The adsorption of formyl (HCO) on Ni(111) is treated using an ab initio embedding theory. HCO, characterized as η 1 -formyl-C, binds strongly to the Ni(111) surface mainly via the carbon atom. Calculated adsorption energies are 59.4, 57.2, and 57.0 kcal/mol at atop, three-fold, and bridge sites, respectively. The minimum energy occurs for an O-C-surface normal angle of 90° and HCO bond angle of 120° at all sites. All calculated C-O stretching frequencies are around 1755 cm - 1 and C-H stretching frequencies are around 2970 cm - 1 . Substantially mixing between Ni 3d orbitals with higher HCO orbitals occurs. η 1 -formyl-O is energetically less stable than η 1 -formyl-C by 18 kcal/mol.