TY - JOUR
T1 - Ab initio energetics of charge compensating point defects
T2 - A case study on MgO
AU - Lin, Shih Kang
AU - Yeh, Chao Kuei
AU - Puchala, Brian
AU - Lee, Yueh Lin
AU - Morgan, Dane
N1 - Funding Information:
Prof. S.-K. Lin gratefully acknowledges financial support from the National Science Council (NSC) in Taiwan (NSC 100-2218-E-006-034) and the US Department of Energy (US DOE), Office of Basic Energy Sciences, Division of Materials Sciences and Engineering (under Award No. DE-SC0001284), each of which supported about half of this work. Dr. Y.-L. Lee gratefully acknowledges financial support from the US Department of Energy (US DOE), Office of Basic Energy Sciences, Division of Materials Sciences and Engineering (under Award No. DE-SC0001284). Dr. B. Puchala gratefully acknowledges financial support from the US Department of Energy (US DOE), Office of Basic Energy Sciences, Division of Materials Sciences and Engineering (under Award No. DE-PS02-07ER07-04). We also gratefully acknowledge computing support from the NSF National Center for Supercomputing Applications Grant No. NCSA-DMR060007. Prof. S.-K. Lin also wishes to thank Dr. A. Heim, Mr. D. Shrader, and Mr. M. Gadre of department of materials science and engineering at university of Wisconsin–Madison for their useful comments and suggestions. The majority of this work was completed while Prof. S.-K. Lin was at the University of Wisconsin–Madison.
PY - 2013
Y1 - 2013
N2 - Density functional theory (DFT) calculations using supercells have proven quite successful in predicting defect properties. Although forming defect groups, for example, the Schottky pair VO••+VMg″ in MgO, are usually energetically favorable in many ionic systems, it is useful to obtain the defect energies of such systems without any defect-defect interactions as reference energies. However, determining non-interacting energies through multi-defect supercell calculations is challenging due to interactions between the defects that are difficult to quantify and can only be avoided by using very large supercells. One solution to this problem is to build an effective multi-defect cell through separate isolated defect calculations, with each defect in their own supercell. However, this isolated defect approach requires that the charge compensation be introduced through charged supercells, and a careful treatment of the cell energetics and electron reference energy is required. In this paper we assess the use of an isolated defect approach for modeling charge-compensating defect groups using the test case of MgO. The appropriate asymptotic condition for the electron reference energy shift is formulated and a method to meet the condition is given. We also demonstrate the strong coupling effect between residual strain energy and electrostatic energy in charged cells, demonstrating that these two effects cannot generally be separated and treated in isolation. The key steps in an approach that yields accurate defect group energies from the isolated defect calculations are presented. The non-interacting Schottky defect formation energy in MgO is determined to be 6.1 eV through calculation of separated isolated charged cells containing VO•• and VMg″, respectively, while the binding energy between the charged defects VO•• and VMg″ is determined to be 1.5 eV. This approach may also be of value for accurate modeling of general isolated defects. The formation energy of an isolated neutral Mg vacancy is found to be lower than that of a Schottky pair, suggesting that it is possible to have significant thermal cation defect formation in MgO without forming charge compensating Schottky pairs.
AB - Density functional theory (DFT) calculations using supercells have proven quite successful in predicting defect properties. Although forming defect groups, for example, the Schottky pair VO••+VMg″ in MgO, are usually energetically favorable in many ionic systems, it is useful to obtain the defect energies of such systems without any defect-defect interactions as reference energies. However, determining non-interacting energies through multi-defect supercell calculations is challenging due to interactions between the defects that are difficult to quantify and can only be avoided by using very large supercells. One solution to this problem is to build an effective multi-defect cell through separate isolated defect calculations, with each defect in their own supercell. However, this isolated defect approach requires that the charge compensation be introduced through charged supercells, and a careful treatment of the cell energetics and electron reference energy is required. In this paper we assess the use of an isolated defect approach for modeling charge-compensating defect groups using the test case of MgO. The appropriate asymptotic condition for the electron reference energy shift is formulated and a method to meet the condition is given. We also demonstrate the strong coupling effect between residual strain energy and electrostatic energy in charged cells, demonstrating that these two effects cannot generally be separated and treated in isolation. The key steps in an approach that yields accurate defect group energies from the isolated defect calculations are presented. The non-interacting Schottky defect formation energy in MgO is determined to be 6.1 eV through calculation of separated isolated charged cells containing VO•• and VMg″, respectively, while the binding energy between the charged defects VO•• and VMg″ is determined to be 1.5 eV. This approach may also be of value for accurate modeling of general isolated defects. The formation energy of an isolated neutral Mg vacancy is found to be lower than that of a Schottky pair, suggesting that it is possible to have significant thermal cation defect formation in MgO without forming charge compensating Schottky pairs.
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U2 - 10.1016/j.commatsci.2013.02.005
DO - 10.1016/j.commatsci.2013.02.005
M3 - Article
AN - SCOPUS:84875419134
SN - 0927-0256
VL - 73
SP - 41
EP - 55
JO - Computational Materials Science
JF - Computational Materials Science
ER -