Absolute band alignment at semiconductor-water interfaces using explicit and implicit descriptions for liquid water

Nicolas G Hörmann,Oliviero Andreussi,Francesco Ambrosio,Alfredo Pasquarello,Nicola Marzari,Zhendong Guo

doi:10.1038/s41524-019-0238-4

Abstract

Quantum mechanical simulations that include the effects of the liquid environment are highly relevant for the characterization of solid-liquid interfaces, which is crucial for the design of a wide range of devices. In this work we present a rigorous and systematic study of the band alignment of semiconductors in aqueous solutions by contrasting a range of hybrid explicit/implicit models against explicit atomistic simulations based on density-functional theory. We find that consistent results are obtained provided that the first solvation shell is treated explicitly. Interestingly, the first molecular layer of explicit water is only relevant for the pristine surfaces without dissociatively adsorbed water, hinting at the importance of saturating the surface with quantum mechanical bonds. By referencing the averaged electrostatic potentials of explicit and implicit water against vacuum, we provide absolute alignments, finding maximal differences of only sim 0.1–0.2 V. Furthermore, the implicit reference potential is shown to exhibit an intrinsic offset of −0.33 V with respect to vacuum, which is traced back to the absence of an explicit water surface in the implicit model. These results pave the way for accurate simulations of solid-liquid interfaces using minimalistic explicit/implicit models.

Highlights

Atomistic insight into the structure, composition and properties of solid-liquid interfaces is paramount for our understanding of the stability or performance of materials in many technological devices, such as chemical sensors, batteries, or fuel cells
We find that the electrostatic potential in the bulk of the implicit model is approximately 0.33 eV below the vacuum level for SCCS3 solvation, which can be explained by the absence of an explicit water surface in implicit models
The findings of this work suggest that the absolute alignment of electrostatic potentials at semiconductor-water interfaces can be determined with an accuracy of $ 0:1 À 0:2 V across different materials and interface terminations using the SCCS implicit water model provided that the first water layer is simulated explicitly

Summary

Introduction

Atomistic insight into the structure, composition and properties of solid-liquid interfaces is paramount for our understanding of the stability or performance of materials in many technological devices, such as chemical sensors, batteries, or fuel cells. Very often, such detailed knowledge can only be obtained from atomistic simulations or from a combination of theory and experiments (e.g., interpretation of spectroscopic measurements). Reasonable agreement between implicit descriptions of water and experiment is typically found for simulations of metallic slabs with respect to interfacial structure, capacitance, potential of zero charge, and interface energetics,[1,4,5,6,10,11,12,13,14,15,16,17] which is related to limited water ordering for ambient temperatures on metals.[18,19,20] For multicomponent semiconductor-water interfaces, on the other hand, rather strong surface-water interactions are more common[21,22,23,24,25,26,27,28] inducing very interface-specific properties of the solvation shell, where the general applicability of implicit solvation is yet to be tested

Methods

Results

Conclusion