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標題: | 假想混三核金屬串錯合物磁學性質的研究 Theoretical Studies on the Magnetic Properties of Hypothetical Ni-M-Ni Type (M = Sc, · · · , Zn) Trimetallic Extended Metal Atom Chains |
作者: | Bang-Ruei Huang 黃邦瑞 |
指導教授: | 金必耀(Bih-Yaw Jin) |
關鍵字: | 金屬串分子,分子磁性,磁性,磁學性質,密度泛函, Extended metal atom chain,EMAC,Molecular magnetism,Density Functional Theory,DFT,Exchange coupling,Exchange parameter,Heisenberg model,HDVV Hamiltonian,Heisenberg-Dirac-Van Vleck Hamiltonian,Van Vleck Equation,Van Vleck Formula, |
出版年 : | 2012 |
學位: | 碩士 |
摘要: | 在 1930 年代,量子力學的出現成為了分子磁性研究的重要里程碑。在 J.H. van Vleck 與 P.W. Anderson 與 L. Noodleman 與多位學者的努力下,我們對於分子磁學性質的 理論研究有了進一步的瞭解。在 1990 年代出現了有趣的金屬串分子,具有分子導線的 潛力與豐富的磁學性質。在本篇論文中,我們基於對鎳三核金屬串分子的瞭解,進一 步對假想混三核金屬串分子的磁學性質做了系統化的研究,也對鎳三核金屬串分子還 原態的磁學性質做了初步的探討。我們使用密度泛函理論來做分子的從頭計算,並採 用 L. Noodleman 的對稱性破缺方法以得到可靠的交換參數 (J),進一步可以得到金屬 串分子不同自旋態的能量差。接著使用 Van Vleck Formula,我們可以模擬出假想混三 核金屬串分子的磁化率如何隨溫度改變而改變。
本篇論文共有三個章節與兩個附錄。在第一章中我們扼要地回顧了分子磁性研究 與鎳三核金屬串分子相關實驗與理論研究的歷史。接著在第二章,我們論述了本篇論 文中使用的理論背景,介紹了 Noodleman 對稱性破缺方法,並交代了密度泛函理論 的從頭計算細節。第三章是主要的研究內容,首先我們以鎳三核金屬串分子為基準, 確認了我們使用理論方法的可靠性。接下來把三個鎳金屬串核心的中間鎳原子系統性 地換成其他第一排過渡金屬,得到一系列的假想混三核金屬串分子。這些假想分子內 金屬原子的不成對電子分佈與結晶場理論吻合;另外,前過渡金屬與後過渡金屬造成 了這些分子的不同自旋態之間的能階分裂差了一個數量級,前過渡金屬造成的能階 分裂是在數千波數 (wavenumber) 的數量級,而後過渡金屬造成的能階分裂是在數百 波數 (wavenumber) 的數量級,這會影響在室溫下不同自旋態的比例分佈。最後,附 錄 A 中摘錄了重要的從頭計算結果,spin contamination 與 spin population 與 charge population;在附錄 B 中我們給出了假想混三核金屬串分子的磁化率如何隨溫度改變 而改變的模擬結果。 Since J.H. van Vleck introduced quantum mechanics on the study of magnetism of molecules in 1932, the related studies on molecular magnetism have prospered thanks to many dedicated scholars such as P.W. Anderson, L. Noodleman, to name a few. In this master thesis we follow their methodologies to provide a systematic study on the magnetic property of hypothetical Ni-M-Ni type trimetallic extended metal atom chains (EMACs), where M denotes the first-row transition metal atoms, based on Noodleman’s broken symmetry method at the level of the density functional theory (DFT). Particularly, a single point ab initio calculation with the crystal geometry is adopted to obtain the exchange parameter, J, more quickly without substantial loss of accuracy. At beginning, we perform a benchmark on calculating the exchange parameter, J, of the trinickel EMACs chloride, Ni3(dpa)4Cl2, and the results are comparable to experi- mental results, which justifies the methodology. We notice the value of J obtained by B3LYP is often lower than experimental value while those obtained by PBE, BP86 are often higher than experimental value, which Benard’s group also reported similar results. Based on the consideration of spin distribution on metal atoms, B3LYP is the better choice to study the magnetic properties of molecules. Beyond Ni3(dpa)4(NCS)2, some related hypothetical systems are explored such as the trinickel atom chain without ligands, (Ni3)6+, and several hypothetical trinickel EMACs with central metal core systematically changed from Sc to Zn, NiMNi(dpa)4(NCS)2. For the latter, the spin population of metals are rationalized in the frame of the crystal field theory. Once the magnetic centers are identified, we have shown how the mediated central metal atom leads to different value of the exchange parameter, J, and different ground state with different spin multiplicities. As far as concerned, there is no experimental investigation of the anion of the trinickel species and here we offer theoretical result of [Ni3(dpa)4(NCS)2]−1, which is found, pos- sibly, to have two stongly ferromagnetic coupled magnetic centers. Finally, we offer a simple simulation of magnetic susceptibility, χ, v.s. temperature, T, by using the van Vleck equation. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/64190 |
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顯示於系所單位: | 化學系 |
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