本文選題：單分子磁體　切入點(diǎn)：量子化學(xué)理論　出處：《南京師范大學(xué)》2016年碩士論文

【摘要】：單分子磁體的慢磁馳豫效應(yīng)和宏觀的量子隧穿效應(yīng)是90年代以來(lái)分子磁學(xué)領(lǐng)域的重大發(fā)現(xiàn),由于其獨(dú)特的磁學(xué)性質(zhì),有望被制作成高密度信息存儲(chǔ)元件或被用于量子計(jì)算,現(xiàn)已經(jīng)成為熱門的研究領(lǐng)域。在本論文中,選擇了近幾年所報(bào)道的具有代表性的幾種單分子磁體,使用量子化學(xué)理論及方法詳細(xì)研究了它們磁各向異性來(lái)源和磁構(gòu)效關(guān)系,希望能為實(shí)驗(yàn)上合成具有較高磁各向異性能壘和阻塞溫度的單分子磁體提供理論指導(dǎo)。首先,研究了一個(gè)八配位Co單分子磁體的磁構(gòu)效關(guān)系,計(jì)算并分析了兩種結(jié)構(gòu)變化對(duì)磁各向異性的影響。探索該分子磁體磁各向異性的來(lái)源和磁各向異性常數(shù)D絕對(duì)值最大時(shí)的可能結(jié)構(gòu)。研究結(jié)果表明：扭轉(zhuǎn)角φ偏離0度越大,dz2和dxy的混合β軌道沿著Co(Ⅱ)上磁軸的方向被拉伸的越厲害,這是該化合物具有較大磁各向異性的原因之一。此外,我們發(fā)現(xiàn)減小α或增大φ都可以增強(qiáng)化合物的磁各向異性,dz2和dxy混合β軌道的電子分布變化圖也驗(yàn)證了這一結(jié)論�；谏鲜鲅芯拷Y(jié)果,我們推測(cè)磁各向異性常數(shù)D絕對(duì)值為最大值時(shí)的可能結(jié)構(gòu)是a=52°且ψ=43°。其次,我們使用B3LYP和DDCI3方法研究了一系列帶有不同配體NHC的二配位COⅠ-N~(-1)化合物[(NHC)CoNDmp](NHC=IPr(1)；cyIPr(2)；sIPr(3)),計(jì)算并研究了它們的交換耦合、磁各向異性和能級(jí)。從理論上探究基于CoⅠ-NⅠ化合物高能壘的來(lái)源。計(jì)算結(jié)果表明CoⅠ-N-Ⅰ化合物的Co和N間具超強(qiáng)的鐵磁相互作用,同時(shí)我們計(jì)算得到的化合物基態(tài)和第一激發(fā)態(tài)的能級(jí)差(分別為275.6、292.9、314.7和383.1 cm~(-1))與實(shí)驗(yàn)上的測(cè)得能壘(分別為215、254和363 cm~(-1))吻合的很好。除此之外,[CoN]~+基團(tuán)的自旋軌道耦合能級(jí)(351.0 cm~(-1))與化合物1-3能級(jí)相差不大,說(shuō)明[CoN]~+固有的大的磁各向異性在化合物的磁各向異性中起著主要作用。這些結(jié)果表明這一系列CoⅠ-N-Ⅰ化合物可以被看成基于[CoN]~+基團(tuán)的單分子磁體,它們較高的能壘主要來(lái)源于[CoN]~+基團(tuán)大的磁各向異性。
[Abstract]:The slow magnetic relaxation effect and macroscopic quantum tunneling effect of monolayer magnets are important discoveries in the field of molecular magnetics since the 1990s. Due to their unique magnetic properties, they are expected to be made into high-density information storage devices or used in quantum computing.Now it has become a hot research field.In this paper, some representative monolayer magnets reported in recent years have been selected, and their magnetic anisotropy sources and magnetic structure-activity relationships have been studied in detail by using quantum chemistry theory and method.It is hoped that it will provide theoretical guidance for the experimental synthesis of monolayer magnets with high magnetic anisotropic barrier and blocking temperature.Firstly, the magnetic structure-activity relationship of an octahedral Co monolayer magnet is studied, and the effects of two structural changes on the magnetic anisotropy are calculated and analyzed.The source of the magnetic anisotropy of the molecular magnet and the possible structure when the absolute value of the magnetic anisotropy constant D is maximum is explored.The results show that the bigger the deviation of torsion angle 蠁 is, the more the mixed 尾 orbital of Dz2 and dxy is stretched along the direction of magnetic axis on Co (鈪，

本文編號(hào)：1727332