交替和非交替纳米酚中的开壳磁态:概念与误解

IF 3.1 Q2 MATERIALS SCIENCE, MULTIDISCIPLINARY
Aristides D. Zdetsis
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引用次数: 0

摘要

与交替纳米相比,非交替纳米石墨烯(NGRs)和石墨烯纳米带(GNRs)无法定义 "子晶格结构",因此在概念和计算上都有很大的简化。这导致了两者之间的一些根本差异。我们在此揭示了非互变 NGR 中被打破的电子-空穴对称性,这是与扭曲的狄拉克点(锥形)及其狄拉克开壳特性密切相关的一个基本差异。我们还通过基于多体(MPn)和耦合簇(CCSD(T))理论的超出普通 DFT 的更高层次计算表明,与文献中的相反报道相反,互变系列围烯(双蒽、围四蒽、围五蒽......等)具有明显的封闭单子基态,这与基于斯通-威尔士(SW)缺陷的非互变异构体形成鲜明对比。我们认为这可以通过亚分子分辨 STM 图像进行实验验证。文献中的误解是由于相关性不足造成的。对于具有反芳香环的非互变 SW-NGRs/GNRs 来说,开壳态和扭曲的狄拉克点(涉及局部电子和脱局域空穴)的驱动力是反芳香性,这是一个充分条件,但并不总是必要条件。这与具有闭壳态的互变异构体的芳香性正好相反。因此,在这两种情况下,亚晶格问题(如亚晶格不平衡或完全缺乏亚晶格)都会导致开壳磁性态;分别是铁磁性(如三角铝)或反铁磁性(如 SW3 × 2、SW4 × 2),而平衡亚晶格(如扶手GNRs、AGNRs)则是无磁(二磁)态。显然,对于由此类 SW 矩阵连接而成的更大 NGR/GNR,反芳香性和电子-空穴对称性的作用也会产生类似的结果。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Open-shell magnetic states in alternant and non-alternant nanographenes: Conceptions and misconceptions

Open-shell magnetic states in alternant and non-alternant nanographenes: Conceptions and misconceptions

In contrast to alternant, in non-alternant nanographenes (NGRs) and graphene nanoribbons (GNRs) no “sublattice structure” can be defined, associated with significant conceptual and computational simplifications. This leads to some fundamental differences between the two. We uncover here the broken electron-hole symmetry in non-alternant NGRs as one fundamental difference closely related to distorted Dirac points (cones) and their diradical open-shell character. We also show by higher level calculations beyond common DFT, based on many-body (MPn) and coupled clusters (CCSD(T)) theory, that the alternant series of peri‑acenes (bisanthene, peri‑tetracene, peri‑pentacene, … etc.), contrary to opposite reports in the literature, have clearly closed singlet ground states, in contrast to their non-alternant isomers based on Stone-Wales (SW) defects. We suggest that this can be experimentally verified by sub-molecularly resolved STM images. The misconceptions in the literature are due to insufficient correlation. For non-alternant SW-NGRs/GNRs with antiaromatic rings the driving force for open-shell states and distorted Dirac points (involving localized electrons and delocalized holes) is antiaromaticity, which is a sufficient but not always necessary condition. This is in juxtaposition to the aromaticity of the alternant isomers with closed shell states. Thus, in both cases sublattice problems, such as sublattice imbalance or complete lack of sublattice would lead to open shell magnetic states; ferromagnetic (e.g. triangulenes), or antiferromagnetic respectively (e.g. SW3 × 2, SW4 × 2), in contrast to non-magnetic (diamagnetic) states for balanced sublattices (e.g. armchair GNRs, AGNRs). Obviously, similar results, regarding the role of antiaromaticity and the broken electron-hole symmetry would be expected for larger NGRs/GNRs obtained by concatenation of such SW-motifs.

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来源期刊
Carbon Trends
Carbon Trends Materials Science-Materials Science (miscellaneous)
CiteScore
4.60
自引率
0.00%
发文量
88
审稿时长
77 days
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