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近年來，二維范德華材料因其豐富性質受到廣泛關注。Fe_nGeTe₂（FGT）是最近發現的一類二維范德華材料，具有室溫下的磁性。然而，FGT類材料的子系統顯示出與位點相關的磁性行為。

Fig. 1 Crystal structure of FenGeTe2 monolayers.

因此，對這類材料的磁性和電子關聯效應進行準確評估是至關重要的。FGT系統的主要特性與其磁性和電子特性密切相關。

Fig. 2 Ji interactions, MAE and TC for FenGeTe2 (n = 3, 4, 5) monolayers computed with different methods.

然而，由于不同Fe亞晶格的磁矩不同，可能會導致某些鐵原子的電子流動性更強。針對FGT的理論計算，目前的研究主要使用標準密度泛函理論（GGA）、包含靜態電子相關性的GGA + U（即DMFT ）方法以及包含動態電子相關性效應的GGA + DMFT方法來研究，但哪種方法最為可靠目前仍未定論。

Fig. 3 Distance dependent isotropic symmetric exchange parameters.

來自瑞典烏普薩拉大學物理與天文系的Sukanya Ghosh等，通過第一性原理計算來分析了不同計算方法對于FGT系統的電子結構和磁學性能。

Fig. 4 Distance dependent anisotropic exchange parameters.

他們的研究結果表明，具有靜態電子相關性的GGA + U得到的晶格參數、磁矩和居里溫度均與實驗有較大偏差，故不適用于FGT系統。而標準GGA得到的磁矩與實驗一致，但居里溫度則被高估許多。

Fig. 5 Comparison of spectral properties of Fe3GeTe2 monolayer.

在GGA + DMFT方法中，加入動態電子相關性以及修改交換關聯作用中的各向同性對稱交換參數后，磁矩幾乎保持不變，而居里溫度卻降低到與實驗結果一致，這說明動力學參數在計算FGT系統的電子結構和磁性性能上是非常有必要的。

Fig. 6 Crystal structure and Jij interactions of bulk Fe3GeTe2

該文近期發布于npj Computational Materials 9: 85(2023)。手機閱讀原文，請點擊本文底部左下角“閱讀原文”，進入后亦可下載全文PDF文件。

Fig. 7 Density of states D(?) of Fe3GeTe2 bulk.

Editorial Summary

DMFT: Accurate calculation of 2D magnetic materials

In recent years, two-dimensional van der Waals materials have attracted extensive attention due to their intriguing properties. Fe_nGeTe₂(FGT), a recently discovered class of two-dimensional van der Waals material, exhibits magnetic behavior at room temperature. However, subsystems belonging to FGT class display site-dependent magnetic properties, necessitating an accurate assessment of their magnetic and electronic effects. The main peculiarity related to all the FGT systems is their site-dependent magnetic and electronic properties. In other words, based on the magnetic moments associated with different Fe sublattices, electrons belonging to some Fe atoms are expected to have more itinerant character than others. Up to this date, researchers have used DFT, DFT?+?U or DMFT approaches, leaving behind the most crucial question unanswered, i.e., which method is the most reliable one to correctly treat the FGT systems.

Fig. 8 Spectral functi on S(k, ?) for bulk Fe3GeTe2.

Sukanya Ghosh et al from the Department of Physics and Astronomy, Uppsala University, performed a first-principles study on the electronic structures and magnetic properties of Fe_nGeTe₂ (n?=?3,?4,?and 5) systems by GGA, LSDA, GGA?+?U and GGA?+?DMFT methods. The results indicated that GGA + U with static electronic correlation yields substantial deviations in lattice parameters, magnetic moments, and Curie temperatures compared to experimental values, rendering it unsuitable for FGT systems. Standard GGA reproduces magnetic moments consistent with experiment, but overestimates Curie temperatures significantly. Upon the inclusion of dynamical electronic correlations within the GGA?+?DMFT approach, the magnetic moments remain almost unchanged, while the exchange interactions, especially the isotropic symmetric exchange parameters get significantly modified to decrease the Curie temperature substantially to have a nice agreement with the experimental results. This study demonstrates that the consideration of dynamical correlations is necessary to capture the correct electronic structure and magnetic behavior of FGT systems. This article was recently published in npj Computational Materials 9: 86 (2023).

原文Abstract及其翻譯

Unraveling effects of electron correlation in two-dimensional Fe_nGeTe₂(n?=?3, 4, 5) by dynamical mean field theory（用動態平均場論闡明二維Fe_nGeTe₂（n = 3,4,5）中的電子關聯效應）

Sukanya Ghosh, Soheil Ershadrad, Vladislav Borisov & Biplab Sanyal

Abstract The Fe_nGeTe₂systems are recently discovered two-dimensional van-der-Waals materials, exhibiting magnetism at room temperature. The sub-systems belonging to Fe_nGeTe₂class are special because they show site-dependent magnetic behavior. We focus on the critical evaluation of magnetic properties and electron correlation effects in Fe_nGeTe₂ (n?=?3, 4, 5) (FGT) systems performing first-principles calculations. Three different ab initio approaches have been used primarily, viz., (i) standard density functional theory (GGA), (ii) incorporating static electron correlation (GGA?+?U) and (iii) inclusion of dynamic electron correlation effect (GGA?+?DMFT). Our results show that GGA?+?DMFT is the more accurate technique to correctly reproduce the magnetic interactions, experimentally observed transition temperatures and electronic properties. The inaccurate values of magnetic moments, exchange interactions obtained from GGA?+?U make this method inapplicable for the FGT family. Correct determination of magnetic properties for this class of materials is important since they are promising candidates for spin transport and spintronic applications at room temperature.

摘要 Fe_nGeTe₂系統是最近發現的二維范德華材料，在室溫下表現出磁性。然而，從屬于Fe_nGeTe₂類的子系統卻顯示出與位點相關的磁性行為。本文著重于對Fe_nGeTe₂（n=3、4、5）（FGT）體系中的磁性能和電子的關聯效應進行研究，研究手段為第一性原理計算。主要采用了三種不同的從頭計算方法，即（i）標準密度泛函理論（GGA）、（ii）包含靜態電子相關性（GGA+U）和（iii）考慮動態電子相關效應（GGA+DMFT）。我們的結果表明，GGA+DMFT的計算結果更加準確，能夠正確重現磁相互作用、轉變溫度和電子性質。而GGA+U計算得出的磁矩、交換相互作用數值不準確，使得該方法不適用于FGT家族。FGT體系材料在室溫下的自旋輸運和自旋器件應用這一領域非常有應用前景，正確計算其磁性性能非常重要。

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原創文章，作者：計算搬磚工程師，如若轉載，請注明來源華算科技，注明出處：http://www.zzhhcy.com/index.php/2023/10/14/024c92eed0/

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DMFT：二維磁性材料的準確計算

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DMFT：二維磁性材料的準確計算

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