本文選題：納米材料 + 密度泛函理論��； 參考：《河北師范大學(xué)》2015年博士論文

【摘要】：硼元素與碳元素非常類似,它也具有豐富的低維構(gòu)形,包括二維平面、一維納米管和零維籠狀結(jié)構(gòu)。這些結(jié)構(gòu)通過某些金屬修飾后,具有良好的儲(chǔ)氫性能,可以在常溫常壓下實(shí)現(xiàn)氫的存儲(chǔ),而備受關(guān)注。另外,硼元素由于具有良好的化學(xué)活性,可以同所有的金屬化合形成形態(tài)各異的化合物。本論文,我們通過不同的方法預(yù)言了一系列的硼化鋰二維結(jié)構(gòu)�；诿芏确汉碚撚�(jì)算,研究了這些結(jié)構(gòu)的電學(xué)特性和儲(chǔ)氫性能。主要內(nèi)容如下:(1)基于一個(gè)穩(wěn)定的結(jié)構(gòu)單元構(gòu)建了兩種穩(wěn)定的、構(gòu)形類似的準(zhǔn)二維平面結(jié)構(gòu)。由于其化學(xué)當(dāng)量為L(zhǎng)i2B5,因此將其命名為L(zhǎng)i2B5-I和Li2B5-II。將Li2B5-II沿著兩個(gè)垂直的方向卷曲,可以得到直徑在4.48-19.59?之間的一系列穩(wěn)定的納米管。和平面結(jié)構(gòu)相比,管狀結(jié)構(gòu)具有更高的熱力學(xué)穩(wěn)定性。隨著納米管直徑的增加,結(jié)構(gòu)的平均原子能先減少后增加,最終與平面結(jié)構(gòu)的平均原子能趨近。對(duì)平面結(jié)構(gòu)和幾個(gè)典型的管狀結(jié)構(gòu)儲(chǔ)氫性能進(jìn)行了分析。結(jié)果顯示,每個(gè)Li原子周圍最多可以吸附兩個(gè)H2分子,儲(chǔ)氫質(zhì)量密度達(dá)10.6wt%。由于Li原子與B原子之間通過離子鍵結(jié)合,離子化的Li原子周圍分布較強(qiáng)的電場(chǎng),對(duì)H2分子具有較強(qiáng)的極化作用,從而實(shí)現(xiàn)對(duì)H2分子的吸附。同時(shí),H2分子與Li之間也有軌道雜化,并且B原子也參與了與H2分子間的相互作用。(2)基于粒子群優(yōu)化算法的晶體結(jié)構(gòu)分析,對(duì)化學(xué)當(dāng)量為L(zhǎng)i2B5二維構(gòu)形進(jìn)行廣泛搜索,得到了兩個(gè)能量最低的異構(gòu)體。這兩種結(jié)構(gòu)的平均原子能相差只有0.0007e V,在計(jì)算允許的誤差范圍內(nèi)。這兩種準(zhǔn)二維平面結(jié)構(gòu),一種B原子框架為平面命名為Planar-sheet,另外一種B原子框架為有起伏的準(zhǔn)平面命名為Buckled-sheet。兩種結(jié)構(gòu)都呈現(xiàn)出金屬性。儲(chǔ)氫性能計(jì)算顯示,Buckled-sheet中每個(gè)Li原子周圍以分子形式吸附3個(gè)H2,平均吸附能為0.19e V,儲(chǔ)氫質(zhì)量密度為15.1wt%。差分電荷密度和Bader電荷分析表明,儲(chǔ)氫作用主要來(lái)源于極化作用和軌道雜化作用。計(jì)算結(jié)果顯示,該結(jié)構(gòu)有望成為高性能的儲(chǔ)氫材料。(3)預(yù)測(cè)了三種Mg B2的金屬夾層硼化鋰結(jié)構(gòu)(分別命名為MS-1、MS-2和MS-3),并對(duì)這三種構(gòu)形的結(jié)構(gòu)穩(wěn)定性進(jìn)行了研究。三種構(gòu)形中的B平面均呈現(xiàn)出規(guī)則的幾何構(gòu)形,一種為已知的β-sheet和一種新的類B2C-sheet。形成能、Bader電荷分析和差分電荷密度均顯示,當(dāng)金屬Li原子位于B平面的六角環(huán)結(jié)構(gòu)的中心頂端位置時(shí),結(jié)構(gòu)更為穩(wěn)定。這同六角環(huán)結(jié)構(gòu)的中B原子的電子缺失有關(guān)�；谧罘�(wěn)定構(gòu)形(MS-1),對(duì)大量金屬硼化物進(jìn)行了結(jié)構(gòu)預(yù)測(cè),發(fā)現(xiàn)四價(jià)金屬的夾層結(jié)構(gòu)較為穩(wěn)定,而最為穩(wěn)定的結(jié)構(gòu)是硼化鐵。
[Abstract]:Boron element is very similar to carbon element, it also has a rich low-dimensional configuration, including two-dimensional plane, one-dimensional nanotubes and zero-dimensional cage structure.After some metal modification, these structures have good hydrogen storage performance, which can realize hydrogen storage at room temperature and atmospheric pressure.In addition, because of its good chemical activity, boron can be combined with all metals to form compounds of different shapes.In this paper, we predict a series of two-dimensional structures of lithium boride by different methods.Based on density functional theory (DFT), the electrical properties and hydrogen storage properties of these structures are studied.The main contents are as follows: (1) two stable quasi-two-dimensional planar structures with similar configuration are constructed based on a stable structural unit.Because its chemical equivalent is Li _ 2B _ 5, it is named as Li2B5-I and Li _ 2B _ 5-II.By curling Li2B5-II in two vertical directions, the diameter of Li2B5-II is 4.48-19.59?Between a series of stable nanotubes.Compared with planar structure, tubular structure has higher thermodynamic stability.With the increase of the diameter of nanotubes, the average atomic energy of the structure first decreases and then increases, and finally approaches the average atomic energy of the planar structure.The hydrogen storage properties of planar structure and several typical tubular structures are analyzed.The results show that at most two H2 molecules can be adsorbed around each Li atom and the mass density of hydrogen storage reaches 10.6 wts.Due to the ionic bonding between Li atom and B atom, the electric field around the ionized Li atom has a strong polarization effect on H _ 2 molecule, thus realizing the adsorption of H _ 2 molecule.At the same time, there is orbital hybridization between H _ 2 molecule and Li, and B atom is also involved in the interaction with H _ 2 molecule.Two isomers with the lowest energy were obtained.The average atomic energy difference between the two structures is only 0.0007e V, within the allowable error range of calculation.The two quasi-two-dimensional planar structures, one of which is named Planar-sheetplane, and the other is Buckled-sheet.The other is the undulating quasi-plane.Both structures exhibit a gold attribute.The calculation of hydrogen storage performance shows that three H _ 2 are adsorbed in molecular form around each Li atom in Buckled-sheet, the average adsorption energy is 0.19 EV, and the mass density of hydrogen storage is 15.1wt.Differential charge density and Bader charge analysis show that hydrogen storage mainly comes from polarization and orbital hybridization.The calculated results show that the structure is expected to be a high performance hydrogen storage material. It can predict the structure stability of three kinds of mg B2 intercalated lithium boride structures (named MS-1MS-2 and MS-3N respectively).The B-plane of the three configurations presents a regular geometric configuration, one is a known 尾 -sheet and the other is a new B2C-sheet-like configuration.The formation energy Bader charge analysis and differential charge density show that the metal Li atom is more stable when it is located at the top of the center of the hexagonal ring structure in the B plane.This is related to the electron deletion of the B atom in the hexagonal ring structure.Based on the structure prediction of a large number of metal boride based on the most stable configuration, it is found that the interlayer structure of tetravalent metal is relatively stable, and the most stable structure is iron boride.
【學(xué)位授予單位】：河北師范大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TQ131.11

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