Theoretical Study of Endohedral Fullerenes M@C 60 (M = Li, Na, or K) in Periodic Boundary Conditions
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Theoretical Study of Endohedral Fullerenes M@C60 (M = Li, Na, or K) in Periodic Boundary Conditions M. H. Gafoura,b,*, K. Saïlb, G. Bassoub, A. Haouzic, and N. Maloufia,d,** a
Université de Lorraine, CNRS, Arts et Métiers Paris Tech, LEM3, Metz, F-57070 France de Microscopie, Microanalyse de la Matière et Spectroscopie Moléculaire (L2MSM), Université Djillali Liabès, Sidi Bel Abbes, Algérie c Laboratoire de Synthèse et Catalyse, Université Ibn Khaldoun, Tiaret, Algérie d Univ Lorraine, Lab Excellence Design Alloy Met Low MAss Struct D, Metz, F-57070 France * e-mail: [email protected] ** e-mail: [email protected]
b Laboratoire
Received January 20, 2020; revised February 18, 2020; accepted February 25, 2020
Abstract—Density functional calculations in periodic boundary conditions (PBCs) were performed to investigate the structural and electronic properties of neutral and charged M@C60 (M = Li, Na, or K). Minimal energy structures for each compounds were obtained. The structural analysis shows that the geometrical shape of the endohedral fullerenes is not perfectly spherical. In the periodic boundary conditions, only K and K+ retain their position in the center of fullerene while (Li) and (Na) are shifted from the center by 1.53 and 0.89 Å respectively. Mulliken population analysis indicated that the M-C60 bond may be purely ionic in the case of encapsulated K and Na, and partly ionic in the case of Li. For all compounds, the highest occupied cluster orbitals (HOCOs), the lowest unoccupied cluster orbitals (LUCOs) and the Gap energy were calculated and compared with literature. The results obtained using PBCs approach show that the simulation model used in this study is indeed appropriate, it not only agrees very well with other theoretical methods but also is consistent with experimental results for C60. Furthermore, this model provide new Gap values for (M@C60) compound (M = Li, Na, or K) that can be used by the scientific community for deriving other electronic properties. DOI: 10.1134/S1063776120090034
1. INTRODUCTION Materials based on π-conjugated organic molecules are increasingly attracting attention for photovoltaic energy research field’s. This phenomenon is justified by their remarkable properties such as low cost, light weight, easy elaboration and compatibility with large scale flexible substrates [1, 2]. Moreover, these materials also represent a clean and cheap source of energy, which is increasingly more efficient [3, 4]. The Fullerene (C60) derivatives, have unique characteristics such as low reduction potential, weak reorganization and preferable stability and display excellent electron accepting ability in photo-induced charge transfer processes [5–7]. Fullerene-based materials can be used in the photovoltaics devices [8–10], electronics field [11–13] and medical applications [14, 15]. Over the last years, the power conversion efficiencies (PCEs) of organic photovoltaics (OPVs) increased quickly and achieved over 10% [16, 17]. The efficiency of photo-conversion
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