Supplemental Material
1. Details of Computational Methods
The first-principle calculations were performed by the VASP code, employing a plane
wave basis set and the PAW potentials to describe the behavior of valence electrons
[S1, S2]. The exchange-correlation energies are described by the Perdew-Wang
(PW91) functions with the generalized gradient approximations (GGA) [S3]. As we
show below, each SDA molecule consists of 32 atoms (16 C atoms, 4 O atoms, 12 H
atoms), with a length of ~15.5 วบ. To simulate the adsorption of SDA chains on
Au(111) and the inter-chain hydrogen bonding, a least number of two SDA chains and
five SDA molecules are required. This corresponds to 180 atoms. Considering the size
of the Au(111) substrate, totally several hundreds of atoms will be involved in this
simulation, which is very demanding for both simulation time and computational
facilities. To reduce the computational burden, we have tried modeling the Au(111)
surface by using a one-layer Au atomic sheet with (111) normal orientation. We find
this is reasonable due to the following two facts: 1) The Au is a noble metal and the
adsorption of SDA on Au is considerably weak, which mainly comes from the
interaction between SDA and the uppermost layer atoms of Au; 2) We have calculated
the adsorption energies of one SDA molecule on one-layer Au(111) sheet (Au atomic
positions are fixed), and one SDA on a three-layer Au(111) slab (with Au atomic
positions fully relaxed). In both cases, the adsorption energies are ~ 0.1 eV, which
corresponds to a physical adsorption. In the structural optimization process, an energy
cut-off of 300 eV is used for the plane waves, and a plane wave cut-off of 400 eV is
used for the calculation of inter-molecular interactions.
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and J. Furthmüller, Comput. Mater. Sci. 6, 15(1996); Phys. Rev. B 54, 11169(1996).
[S2] P. E. Blöchl, Phys. Rev. B 50, 17953 (1994); G. Kresse and D. Joubert, Phys. Rev.
B 59, 1758 (1999).
[S3] J. P. Perdew, J. A. Chevary, S. H. Vosko, K. A. Jackson, M. R. Pederson, D. J.
Singh, and C. Fiolhais, Phys. Rev. B 46, 6671(1992).