Force Field Parameter Development for the Thiolate/Defective Au(111) Interface

A molecular-level
understanding of the interplay between self-assembled
monolayers (SAMs) of thiolates and gold surface is of great importance
to a wide range of applications in surface science and nanotechnology.
Despite theoretical research progress of the past decade, an atomistic
model, capable of describing key features of SAMs at reconstructed
gold surfaces, is still missing. In this work, periodic ab initio
density functional theory (DFT) calculations were utilized to develop
a new atomistic force field model for alkanethiolate (AT) SAMs on
a reconstructed Au(111) surface. The new force field parameters were
carefully trained to reproduce the key features, including vibrational
spectra and torsion energy profiles of ethylthiolate (C2S) in the bridge or staple motif model on the Au(111) surface, wherein,
the force constants of the bond and angle terms were trained by matching
the vibrational spectra, while the torsion parameters of the dihedral
angles were trained via fitting the torsion energy profiles from DFT
calculations. To validate the developed force field parameters, we
performed classical molecular dynamics (MD) simulations for both pristine
and reconstructed Au–S interface models with a (2√3
× 3) unit cell, which includes four dodecanethiolate (C10S) molecules on the Au(111) surface. The simulation results showed
that the geometrical features of the investigated Au–S interface
models and structural properties of the C10S SAMs are in
good agreement with the ab initio MD studies. The newly developed
atomistic force field model provides new fundamental insights into
AT SAMs on the reconstructed Au(111) surface and adds advancement
to the existing interface research knowledge.