The first-principle technique has been employed to determine the structure of hexyl thiolate molecular chains, monolayers and the adsorption system. CASTEP calculation shows that hexyl thiolate monolayer is a self-assembly system. And the molecular orientation of the hexyl thiolate on the surface is not symmetrical, they have the simplex structure. The electron density confirms the result. Hexyl thiolate monolayer is adsorbed on the Au(1 1 1)-(root 3 x root 3)R30 degrees surface in the bridge site with the angle between the S-C6 bond and the surface is 65. The structural parameters in the adsorption system are the same to those in the monolayer. (C) 2015 Elsevier B.V. All rights reserved.