1,720,954 research outputs found
Charge Density Study of a Spin Crossover Complex, trans-[Fe(abpt)2(NCS)2], a Mixed High Spin and Low Spin State
No full text多相晶體trans-[Fe(abpt)2(NCS)2] phase D之晶體結構中，存在兩個不對稱相關的單核分子；兩分子個別以鐵為對置中心，其一Fe原子會隨溫度降低而有自高自旋 (S=2)到低自旋狀態 (S=0)的自旋轉換現象(Tc=162 K)；另一Fe'原子則在量測的溫度範圍維持者高自旋的順磁狀態。兩個單核分子主要的差別在於配位基abpt(abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole)上的平面度；介於未配位的吡啶(pyridine)和疊氮基(triazole)之間的雙面角(dihedral angle)在低溫結構(90 K)分別為6.2度(Fe)及20.1度(Fe')。
由於兩個分子在低溫下的電子組態十分不同，我們利用X-ray單晶繞射技術及DFT理論計算來研究其電子密度的分布。經過電子密度拓樸分析研究，我們可以觀察到在兩個分子間，中心金屬d電子軌域分佈的不同；Fe由於處在低自旋狀態所以在二次電子微分(Laplacian)圖中呈現非球性對稱分佈，Fe'則處於高自旋狀態所以二次電子微分(Laplacian)圖呈現較為球形對稱分佈。理論計算的結果相當符合實驗所得到的結果。
為了瞭解兩分子在低溫下呈現不同磁性及結構的成因，我們利用DFT理論計算的方式觀察其在熱力學上的不同；更進一步的，我們可以粗估其自旋轉換發生的溫度(spin-flip temperature)。由於配位基abpt的平面度在兩分子中存在一定的差異，我們試圖以費米孔洞分析去了解兩分子中兩芳香環上π電子共振的不同。此外，我們可以觀察雙面角的改變對中心金屬和配位氮距離影響。最後，我們利用ADF程式模擬出低自旋-低自旋(LS-LS)的結構，試圖以能量及結構上的觀點去了解磁性轉換的關係。A polymorph D of the complex trans-[Fe(abpt)2(NCS)2], (abpt = 4-amino-3,5 bis(pyridine-2-yl)-1,2,4-triazole)was synthesized and structurally characterized. There are two unique mononuclear molecules in the crystal lattice, one (Fe) undergoes a gradual thermal spin transition from high spin (HS) to low spin (LS) state around 162 K, while the other (Fe') remains in HS at the temperature range of 300-2K. The main difference in these two molecules is the planarity of the abpt ligand; the dihedral angle between the triazole ring and the uncoordinated pyridine ring is 6.2 and 20.1º for Fe and Fe' complex respectively.
In order to understand the differences in electronic density distribution between these HS and LS states, trans-[Fe(abpt)2(NCS)2] polymorph D is chosen to be the ideal case to investigate the charge density using single crystal X-ray diffraction at 90 K. The electron density can also be calculated by DFT calculation. Through the topological analysis on charge density derived from both experimental measurement and quantum calculation, we are able to demonstrate the apparent differences in the environment of metal ion in two states. Furthermore, the d-orbital populations at HS (Fe) and LS (Fe') states can also be derived. The agreement between the experiment and theory is reasonably good. The relationship between the planarity of the ligand, abpt, and the π electron conjugation is depicted in terms of Fermi-hole distribution.
The difference of ~0.2Ǻ in Fe–N distance is often observed between HS and LS states. The significant difference in the intra-ligand dihedral angle in this case is also highly correlated with the magnetic behaviour. A few models based on such consideration are calculated to rationalize the HS-LS transition. The energies of HS-HS; HS-LS and LS-LS pairs are computed accordingly; the absence of LS-LS case in this compound can be realized. The spin-flip temperature can be predicted.目錄
中文摘要 Ⅰ
英文摘要 Ⅱ
目錄 Ⅲ
表目錄 Ⅴ
圖目錄 Ⅶ
第一章. 序 論 1
第二章. 原 理 5
2-1. X-ray單晶繞射 5
2-2. 多極模型與靜電荷分析 7
2-2-1. 單極精算 7
2-2-2. 多極精算 8
2-2-3. 淨電荷分析 9
2-3. 量子理論計算原理 10
2-3-1. HF-SCF簡介 10
2-3-2. Ab initio Calculation by Density Functional Theory 12
2-3-3. 量子化學計算中的基底函數組 15
2-3-4. 費米孔洞函數(Fermi-hole distribution)16
2-4. 拓樸學分析原理 17
2-4-1. Atoms in Molecules Theory 17
2-4-2. 臨界點的定義 19
2-4-3. 原子空間和鍵結路徑(atomic basin & bond path) 21
2-4-4. vs. 化學鍵 22
第三章. 自旋交叉錯合物[Fe(abpt)2(NCS)2] phase D的結構探討 24
3-1. 實驗方法 24
3-1-1. 合成與養晶 24
3-1-2. X-ray繞射實驗 24
3-1-3. 吸收校正 25
3-1-4. 變溫磁性量測 28
3-2. 結構解析 29
3-2-1. 室溫及低溫結構討論 29
3-2-2. [Fe(abpt)2(NCS)2] polymorph A、B、C、D結構之比較 37
3-3. 量子理論計算 39
3-3-1基底函數之選擇 40
3-3-2. trans-[Fe(abpt)2(NCS)2]的單點計算及幾何優選
及[HS-HS]、[HS-LS]、[LS-LS]相對能量及結構比較 41
3-3-3. 配位基雙面角的改變對[Fe(abpt)2(NCS)2]磁性改變影響和[HS-HS]、[HS-LS]、[LS-LS]相對能量及結構比較 42
3-3-4. 變溫紅外線光譜研究實驗數據與理論計算比較之研究 45
3-3-5. 理論計算觀察Entropy在室溫及低溫隨自旋轉換變化 48
第四章. 自旋交叉錯合物[Fe(abpt)2(NCS)2]的電荷密度分析 52
4-1. 多極模型精算 52
4-2. 拓樸學分析 53
4-2-1. 剩餘電子密度 53
4-2-2. Fe-N鍵結電子密度拓樸學分析 55
4-2-3. 淨電荷分佈和d-軌域電子分佈(d-orbital population) 58
4-2-4. 電子密度分佈之理論計算 61
4-3. 費米孔洞分析(Fermi-hole Distribution Analysis) 65
第五章. 結論 69
參考文獻 70
附錄 7
The photo-induced commensurate modulated structure in site-selective spin crossover complex trans-[Fe(abpt)(2)(NCS)(2)]
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
