We have systematically carried out a density functional theory-based investigation to understand the structural and electronic properties of various fused metalloporphyrin nanotubes (MPNT; M = Sc and Ti) by varying their diameters ranging from 7.91 Å to 18.70 Å for ScPNT and 7.90 Å to 18.59 Å for TiPNT. Binding energies and curvature energies are calculated to access the binding strength and stability of the nanotubes (NTs). From band structure and density of states, it is observed that the ScPNTs are metallic in nature and TiPNTs are semiconductors with small band gaps. The energy gap increases with increasing tube diameter. Our study also indicates that the transition metal atoms play an important role in determining the electrical nature (metallic or semiconducting) of the NTs. Furthermore, work functions for the fused NTs are found to decrease with increasing tube diameter. These results may have direct relevance to the technological applications in terms of band gap engineering or controlled thermionic emission.

中文翻译：

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稠合卟啉纳米管的直径相关结构和电子特性：密度泛函研究

我们系统地进行了基于密度泛函理论的研究，以了解各种熔融金属卟啉纳米管（MPNT；M = Sc 和 Ti）的结构和电子特性，方法是将 ScPNT 的直径范围从 7.91 Å 到 18.70 Å 和 7.90 Å 到TiPNT 为 18.59 Å。计算结合能和曲率能以获取纳米管 (NT) 的结合强度和稳定性。从能带结构和态密度可以看出，ScPNTs本质上是金属的，而TiPNTs是具有小带隙的半导体。能隙随着管径的增加而增加。我们的研究还表明，过渡金属原子在决定 NTs 的电性质（金属或半导体）方面起着重要作用。此外，发现融合NT的功函数随着管直径的增加而减小。这些结果可能与带隙工程或受控热电子发射方面的技术应用直接相关。