2023-01-012024-05-13https://scholars.lib.ntu.edu.tw/handle/123456789/651622本項目旨在利用第一性原理模擬研究複雜週期材料（共軛聚合物、金屬有機骨架、有機無機雜化鈣鈦礦和低維材料等）的基本性質，特別是電子和振動（聲子）特性。 最近，金屬有機骨架 (MOF) 的寬帶介電響應成為一個新興問題，可能對太赫茲傳感器和便攜式光電子產品的發展產生積極影響。強烈要求進行實驗工作，但是，由於尚未很好地建立對這種複雜週期系統的理論模擬方法，因此 MOF 頻率依賴性介電特性的詳細起源仍然受到限制。特別是，對複雜 MOF 中頻率相關的介電與電子和/或振動特性之間關係的全面理解仍然非常難以捉摸。因此，有必要建立復雜 MOF 的頻率相關介電特性的理論概念，並探索實用的模擬方法，這些都是具有挑戰性的問題。 我在下一個資助期間的遠景計劃旨在建立頻率相關的介電函數與包括 MOF 的振動和電子特性在內的特徵之間的關係。我將特別關注：(i) 系統地探索介電函數的實部與 IR 模式之間的關係，提供對介電特性與振動特徵相關的物理機制的全面見解，(ii) 虛部之間的聯繫闡明了介電函數和能帶結構的一部分，提供了對將介電特性與電子特性聯繫起來的下劃線機制的見解。在這裡，我打算將原子軌道分析應用於第一性原理模擬（平面波）結果，並研究對介電特性和聲子特性做出重要貢獻的原子軌道的起源。 作為該項目的第二個目標，我的目標是尋找 VTe2 晶體的五邊形構象，這是有吸引力的 TMD 候選者之一。在我們的初步結果中，通過用 V 代替金屬 Pd 並用 Te 原子代替非金屬 Se，從層狀五角 PdSe2 創建了初始 VTe2 單層。然後所有的晶格參數、對稱性和原子位置都得到了充分優化。令人驚訝的是，形成了一種獨特的具有方形構象的 VTe2 單層 (s-VTe2)，這是一種以前未報導的新型 2D 單層。晶胞具有三斜晶格並包含兩個釩 (V) 離子，每個離子與四個碲 (Te) 原子結合，形成金字塔形多面體單元。 s-VTe2 的結構可以看作是由兩個 Te 原子子層和一個 V 離子子層組成的原子三層結構。所有三個子層都具有類似正方形的配置，其特徵不同於以前眾所周知的 TMD 多晶型物，甚至是五角形的。計算出的STM圖像清晰呈現正方形拓撲結構，表明結構的投影。簡而言之，一種新的單層 s-VTe2 展示了一種獨特的結構，具有獨特的“方形”拓撲結構，這在 VX2（X=S、Se、Te）或其他 TMD 中都不明顯。 The present project aims to investigate, using the first-principle simulation, fundamental properties of complex periodic materials (conjugated polymers, metal-organic frameworks, organic-inorganic hybrid perovskites, and low-dimensional materials, etc.), in particular, the electronic and vibrational (phonon) property. Recently, the broadband dielectric response of metal-organic frameworks (MOFs) becomes an emerging issue that could bring a positive impact on the development of terahertz sensors and portable optoelectronics. The experimental efforts have been intensively urged, however, the detailed origin of the frequency-dependent dielectric property of MOFs is still limited due to the fact that a theoretical simulation method on such complex periodic systems has not yet been established well. In particular, a comprehensive understanding of the relationship between frequency-dependent dielectric and electronic and/or vibrational properties in complex MOFs remains greatly elusive. It is, therefore, necessary to both establish a theoretical concept of the frequency-dependent dielectric property of complex MOFs and explore practical simulation approaches are challenging issues. My perspective plan during the next funding period intends to establish the relationship between the frequency-dependent dielectric function and characteristic features including the vibrational and electronic properties of MOFs. In particular, I will focus on: (i) the relationships between the real part of the dielectric function and IR modes are systematically explored, providing comprehensive insights into the physical mechanisms correlating dielectric property and vibrational features, (ii) the connections between the imaginary part of the dielectric function and band structure are elucidated, providing insights into the underline mechanisms linking the dielectric property to the electronic property. Here I intend to apply the atomic orbital analysis to the first principle simulation (plane-wave) results and investigate the origin of the atomic orbitals that make a crucial contribution to dielectric property and phonon features. As the second target of this project, I aim to search for a pentagonal conformation of VTe2 crystal which is one of the attractive TMD candidates. In our preliminary results, an initial VTe2 monolayer was created from the layered pentagonal PdSe2 by replacing the metallic Pd with V and non-metallic Se with Te atom. Then all of the lattice parameters, symmetry, and atomic positions were fully optimized. Surprisingly, a unique VTe2 monolayer with a square-like conformation (s-VTe2) was formed that is a previously unreported new 2D single-layer. The unit cell has the triclinic lattice and contains two Vanadium (V) ions, each binds to four Tellurium (Te) atoms, forming in the pyramidal polyhedron unit. The structure of s-VTe2 can be viewed as the assembly of an atomic trilayer consisting of two sublayers of Te atoms and one sublayer of V ions. All three sublayers possess a square-like configuration, which features are different from the previously well-known TMDs polymorphs and even pentagonal ones. The calculated STM image clearly presents the square topology, indicating the projection of the structure. In short, a new monolayer s-VTe2 exhibits a unique structure with a distinctive “square-like” topology not apparent in either VX2 (X=S, Se, Te) or other TMDs.第一性原理模擬;電子結構;振動特性;金屬有機框架;VTe2 單層。;First-principle simulation; electronic structure; vibrational property; metal−organic frameworks; VTe2 monolayer.