Transferable Gaussian Attractive Potentials for Organic/Oxide Interfaces

Organic/oxide interfaces play an
important role in many areas of
chemistry and in particular for lubrication and corrosion. Molecular
dynamics simulations are the method of choice for providing complementary
insight to experiments. However, the force fields used to simulate
the interaction between molecules and oxide surfaces tend to capture
only weak physisorption interactions, discarding the stabilizing Lewis
acid/base interactions. We here propose a simple complement to the
straightforward molecular mechanics description based on “out-of-the-box”
Lennard-Jones potentials and electrostatic interactions: the addition
of an attractive Gaussian potential between reactive sites of the
surface and heteroatoms of adsorbed organic molecules, leading to
the Gaussian Lennard-Jones (GLJ) potential. The interactions of four
oxygenated and four amine molecules with the typical and widespread
hematite and γ-alumina surfaces are investigated. The root mean
square deviation (RMSD) for all probed molecules is only 5.7 kcal/mol,
which corresponds to an error of 23% over hematite. On γ-alumina,
the RMSD is 11.2 kcal/mol using a single parameter for all five chemically
inequivalent surface aluminum atoms. Applying GLJ to the simulation
of organic films on oxide surfaces demonstrates that the mobility
of the surfactants is overestimated by the simplistic LJ potential,
while GLJ and other qualitatively correct potentials show a strong
structuration and slow dynamics of the surface films, as could be
expected from the first-principles adsorption energies for model head
groups.