Optical gap and native point defects in kaolinite studied by the GGA-PBE, HSE functional, and GW approaches

• Published in: Physical review. B, Condensed matter and materials physics Vol. 84; no. 7; p. 075120
• Main Authors: Nisar, Jawad, Århammar, C., Jämstorp, Erik, Ahuja, Rajeev
• Format: Journal Article
• Language: English
• Published: 08-08-2011
• Subjects: 1ST-PRINCIPLES; ADSORPTION; AUGMENTED-WAVE METHOD; BAND-GAPS; BOEHMITE; DIFFRACTION; ELECTRON; Engineering Science with specialization in Nanotechnology and Functional Materials; EXCHANGE; Fysik; INITIO MOLECULAR-DYNAMICS; Materials science; NATURAL SCIENCES; NATURVETENSKAP; Physics; REFINEMENT; TECHNOLOGY; TEKNIKVETENSKAP; Teknisk fysik med inriktning mot nanoteknologi och funktionella material; Teknisk materialvetenskap
• ISSN: 1098-0121; 1550-235X; 1550-235X
• DOI: 10.1103/PhysRevB.84.075120

The electronic structure of kaolinite with and without intrinsic defects has been studied by the Perdew-Burke-Ernzerhof (PBE) and Heyd-Scuseria-Ernzerhof (HSE) functionals and by the G 0 W 0 approach. The band gap of defect-free kaolinite was estimated to between 6.2 and 8.2 eV. Analysis of the formation energy of native point defects in kaolinite was carried out under different growth conditions. When the PBE defect formation energy as a function of temperature is considered, the hydroxyl vacancy is compensated by a hydrogen vacancy at a formation energy of 0.45 eV at oxygen-rich and hydrogen-poor conditions. The hydroxyl vacancy acts as a donor whereas the hydrogenvacancy acts as an acceptor, both inducing states in the band gap. The HSE03 hybrid functional increases the defect formation energy and tends to localize and move these states away from the band edges, as compared to the other two methods. Our results imply that intrinsic defects will tune the band gap of kaolinite and influence properties related to its band structure such as the cation retention capability and drug release.