Structural and Electronic Properties of Different Terminations for Quartz (001) Surfaces as Well as Water Molecule Adsorption on It: A First-Principles Study

Structural and electronic properties of Si termination, O-middle termination, and O-rich terminations of a quartz (001) surface as well as water molecule adsorption on it were simulated by means of density functional theory (DFT). Calculated results show that the O-middle termination exposing a single oxygen atom on the surface is the most stable model of quartz (001) surface, with the lowest surface energy at 1.969 J.m(-2), followed by the O-rich termination and Si termination at 2.892 J.m(-2) and 2.896 J.m(-2), respectively. The surface properties of different terminations mainly depend on the surface-exposed silicon and oxygen atoms, as almost all the contributions to the Fermi level (E-F) in density of states (DOS) are offered by the surface-exposed atoms, especially the O2p state. In the molecular adsorption model, H2O prefers to adsorb on the surface Si and O atoms, mainly via O-1-H-1 bond at 1.259 angstrom and Si-1-O-w at 1.970 angstrom by Van der Waals force and weak hydrogen bond with an adsorption energy of -57.89 kJ.mol(-1). In the dissociative adsorption model, the O-middle termination is hydroxylated after adsorption, generating two new Si-OH silanol groups on the surface and forming the OwH2 center dot center dot center dot O-4 hydrogen bond at a length of 2.690 angstrom, along with a large adsorption energy of -99.37 kJ.mol(-1). These variations in the presence of H2O may have a great influence on the subsequent interfacial reactions on the quartz surface.