17:15 〜 19:15
[HCG20-P07] Density Functional Theory Study of Iron Sulfide Containing Selenium
キーワード：Density Functional Theory, Simulation, Iron Sulfide, Selenium
In the geological disposal of high-level nuclear waste, selenium (Se) 79 is a long-lived radionuclide (half-life 2.95×105 years), and it is important for safety assessment to understand its behavior in the environment. Recently, the phenomenon of Se being incorporated into mackinawite was observed. Extended X-ray Absorption Fine Structure (EXAFS) measurements were used to observe the atomic arrangement around Se, but the details are unknown. It is not easy to obtain further detailed information through observation.
In this study, we evaluated the distribution of Se incorporated into mackinawite using density functional theory (DFT) simulations. We used the Vienna Ab initio Simulation Package (VASP) [1] for the first-principles calculations—the geometric optimization of the mackinawite models with different Se configurations. From the calculation, it was revealed that the close Se–Se distance increases energy. This result implies that Se tends to be distributed sparsely in mackinawite.
Next, we evaluated EXAFS spectra of the geometrically optimized mackinawite models with two Se. We used FEFF [2] and Larch [3] software to evaluate the EXAFS spectra of the mackinawite models. We conducted a Fourier transformation (FT) from the k–space to the R–space with three different ranges in the k–space: 3–8, 3–10, and 3–14 Å-1. We found that the 2nd and 3rd peaks reflect the position of Se in mackinawite. It was found that the shape of the EXAFS spectra depends on the range in k-space. However, the difference among them was not large, i.e., it is difficult to identify the Se position in mackinawite by EXAFS experiments.
From these results, more detailed DFT simulations are effective in determining the Se configuration in mackinawite. We will present further developments in our simulations, including edge structure, thermal effects, etc.
Acknowledgment
The Ministry of Economy, Trade, and Industry of Japan has funded a part of the work as “Project on Research and Development for Validating Safety Assessment of Geological Disposal: Development of the Technology for Integrating Radionuclide Migration Assessments” (Grant Number: JPJ007597, Fiscal Year 2023-2024).
References
[1] Kresse & Hafner, Phys. Rev. B 47, 558(R) (1993); Kresse & Hafner, Phys. Rev. B 49, 14251 (1994); Kresse & Furthmüller, Comput. Mater. Sci. 6, 15 (1996); Kresse & Furthmüller, Phys. Rev. B 54, 11169 (1996).
[2] Ankudinov & Rehr, Phys. Rev. B 56, R1712 (1997).
[3] M. Newville, J. Phys.: Conf. Series 430, 012007 (2013).
In this study, we evaluated the distribution of Se incorporated into mackinawite using density functional theory (DFT) simulations. We used the Vienna Ab initio Simulation Package (VASP) [1] for the first-principles calculations—the geometric optimization of the mackinawite models with different Se configurations. From the calculation, it was revealed that the close Se–Se distance increases energy. This result implies that Se tends to be distributed sparsely in mackinawite.
Next, we evaluated EXAFS spectra of the geometrically optimized mackinawite models with two Se. We used FEFF [2] and Larch [3] software to evaluate the EXAFS spectra of the mackinawite models. We conducted a Fourier transformation (FT) from the k–space to the R–space with three different ranges in the k–space: 3–8, 3–10, and 3–14 Å-1. We found that the 2nd and 3rd peaks reflect the position of Se in mackinawite. It was found that the shape of the EXAFS spectra depends on the range in k-space. However, the difference among them was not large, i.e., it is difficult to identify the Se position in mackinawite by EXAFS experiments.
From these results, more detailed DFT simulations are effective in determining the Se configuration in mackinawite. We will present further developments in our simulations, including edge structure, thermal effects, etc.
Acknowledgment
The Ministry of Economy, Trade, and Industry of Japan has funded a part of the work as “Project on Research and Development for Validating Safety Assessment of Geological Disposal: Development of the Technology for Integrating Radionuclide Migration Assessments” (Grant Number: JPJ007597, Fiscal Year 2023-2024).
References
[1] Kresse & Hafner, Phys. Rev. B 47, 558(R) (1993); Kresse & Hafner, Phys. Rev. B 49, 14251 (1994); Kresse & Furthmüller, Comput. Mater. Sci. 6, 15 (1996); Kresse & Furthmüller, Phys. Rev. B 54, 11169 (1996).
[2] Ankudinov & Rehr, Phys. Rev. B 56, R1712 (1997).
[3] M. Newville, J. Phys.: Conf. Series 430, 012007 (2013).