Prediction of semiconductor band edge positions in aqueous environments from first principles

Yabi Wu, M. K. Y. Chan, and G. Ceder

Phys. Rev. B 83, 235301 – Published 1 June 2011

Abstract

The ability to predict a semiconductor's band edge positions in solution is important for the design of water-splitting photocatalyst materials. In this paper, we introduce a first-principles method to compute the conduction-band minima of semiconductors relative to the water $H_{2}$ O/H $_{2}$ level using density functional theory with semilocal functionals and classical molecular dynamics. We test the method on six well known photocatalyst materials: TiO $_{2}$ , WO $_{3}$ , CdS, ZnSe, GaAs, and GaP. The predicted band edge positions are within 0.34 eV of the experimental data, with a mean absolute error of 0.19 eV.

Received 24 January 2011

DOI:https://doi.org/10.1103/PhysRevB.83.235301

Authors & Affiliations

Yabi Wu¹, M. K. Y. Chan^1,2, and G. Ceder^1,*

¹Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
²Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, USA

^*Author to whom all correspondence should be addressed:gceder@mit.edu

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Vol. 83, Iss. 23 — 15 June 2011

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Images

Figure 1
A schematic diagram of possible band level arrangements for water-splitting photocatalysts. (a) Favorable band level arrangement; (b) unfavorable VBM position; (c) unfavorable CBM position.Reuse & Permissions
Figure 2
A schematic diagram of the band alignment at the semiconductor-water interface. ${Ec}_{bulk}$ $=$ CBM in the bulk of the semiconductor, ${Ec}_{edge}$ $=$ CBM at the semiconductor-solution interface, $A_{bulk}$ $=$ acceptor level (H $_{2}$ O/H $_{2}$ level of liquid water in this work) in the bulk of the solution, $A_{edge}$ $=$ acceptor level at the semiconductor-solution interface, $H_{semi_bulk}$ $=$ Hartree potential in the semiconductor bulk, $H_{semi_edge}$ $=$ Hartree potential on the semiconductor side at the semiconductor-solution interface, $H_{sol_bulk}$ $=$ Hartree potential in the bulk of the solution, and $H_{sol_edge}$ $=$ Hartree potential on the solution side at the semiconductor-solution interface.Reuse & Permissions
Figure 3
Total DOS plots for (a) a 128 $H_{2}$ O molecules liquid system with MD atomic configurations at $t$ $=$ 50 ps without DFT relaxation, with a band gap of 3.76 eV; (b) a 128 $H_{2}$ O molecules liquid system with MD atomic configurations at $t$ $=$ 100 ps without DFT relaxation, with a band gap of 3.89 eV; (c) a 128 $H_{2}$ O molecules liquid system with MD atomic configurations at $t$ $=$ 100 ps with DFT relaxations, with a band gap of 3.89 eV. $E_{v}$ is the VBM energy.Reuse & Permissions
Figure 4
DOS plots for a 127H $_{2}$ O $+$ $H_{3}$ O $^{+}$ liquid system. The black solid line is the total DOS while the red dashed line is the projected DOS from the $H_{3}$ O $^{+}$ ion in this system. We enlarged the $H_{3}$ O $^{+}$ DOS 30 times to make it visible on the scale of the total DOS. The DOS peak at approximately 2.0 eV represents the LUMO of the system contributed by the $H_{3}$ O $^{+}$ ion. $E_{v}$ is the VBM energy.Reuse & Permissions
Figure 5
Calculated Hartree potential profile of a stoichiometric TiO $_{2}$ -water slab system. The vertical green dashed line indicates the interface. The left side is semiconductor TiO $_{2}$ and the right side is water. The black solid line is the planar-averaged Hartree potential as a function of cell dimension normal to the interface. The red dashed line with square markers indicates the planar-averaged Hartree potential of TiO $_{2}$ , $H_{semi_edge}$ . The blue dashed line with circular markers indicates the planar-averaged Hartree potential of liquid water, $H_{sol_edge}$ .Reuse & Permissions
Figure 6
CBM band edge level results referenced to the NHE. Blue lines are computational results by the method in this paper. Red lines are experimental data from Refs. 21 and22. Two dotted lines indicate the $H_{2}$ O/H $_{2}$ and $H_{2}$ O/O $_{2}$ levels in water.Reuse & Permissions

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