Relating Interfacial Order to Sum Frequency Generation with Ab Initio Simulations of the Aqueous Al2O3(0001) and (112̅0) Interfaces

Abstract

We use density functional theory molecular dynamics simulations to investigate the structure, dynamics, and vibrational sum frequency generation (vSFG) spectra at the Al2O3(0001)–H2O and Al2O3(1120)–H2O interfaces. We find that the differences in the vSFG spectra between the two interfaces can be explained by significantly weaker surface–water interactions at the (0001) vs (1120) interface. The weaker interactions at the (0001) surface are caused by the flat surface plane and high density of OH groups, leading to a decoupling of the vibrational modes of the surface OH groups and H2O molecules. The (0001) vSFG spectrum thus displays two well-separated peaks at the near-neutral pH, in contrast to the vSFG spectrum of the corrugated (1120) interface, which has stronger surface–water interactions and thereby a narrower band in the vSFG spectrum with closely spaced peaks. By simulating the interfaces with both the Perdew–Burke–Ernzerhof (PBE)–Tkatchenko–Scheffler and revised PBE (RPBE) functionals, we find ...