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Probe Type II Band Alignment in One-Dimensional Van Der Waals Heterostructures Using First-Principles Calculations
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Defect energy levels in density functional calculations: alignment and band gap problem.

Audrius Alkauskas1, Peter Broqvist, Alfredo Pasquarello

  • 1Ecole Polytechnique Fédérale de Lausanne (EPFL), Institute of Theoretical Physics, CH-1015 Lausanne, Switzerland.

Physical Review Letters
|September 4, 2008
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Summary

We compared defect energy levels using two density-functional schemes, finding close correspondence even with varying band gaps. This work offers a guideline for comparing calculated and experimental defect levels in materials science.

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Area of Science:

  • Materials Science
  • Computational Physics
  • Quantum Chemistry

Background:

  • Accurately calculating defect energy levels is crucial for understanding material properties.
  • Density-functional theory (DFT) methods often suffer from the 'band gap problem', affecting defect level predictions.
  • Semilocal and hybrid functionals offer different approaches to approximating exchange-correlation interactions.

Purpose of the Study:

  • To compare the accuracy of semilocal and hybrid density-functional schemes for calculating defect energy levels.
  • To investigate how calculated defect levels shift as the band gap approaches experimental values.
  • To provide a guideline for comparing theoretical defect levels with experimental data.

Main Methods:

  • Calculations of atomically localized defect energy levels using semilocal and hybrid density-functional schemes.
  • Analysis of defect level shifts with varying band gaps, particularly when approaching experimental values.
  • Comparison of defect levels derived from total-energy differences under suitable alignment.

Main Results:

  • Defect levels calculated from both schemes show close correspondence when suitably aligned, with average shifts of at most 0.2 eV.
  • The shifts are largely independent of the material's band gap.
  • Deviations from ideal alignment systematically increase with the spatial extent of the defect wave function.

Conclusions:

  • Hybrid density-functional schemes offer an improvement by partially mitigating the band gap problem.
  • The study provides a reliable method for comparing theoretical and experimental defect levels.
  • Understanding these shifts is key for accurate materials design and characterization.