Surprising Findings for Ce Doped Fullerenes and Understanding of Experiments through Theoretical Modelling A DFT Approach

• Endohedral fullerenes; which have one metal atom encapsulated; are relatively well studied compared to species that have two elements inside the cage.1-5 Cerium; the most reactive elements of the rare earth group can be encapsulated into fullerene (C78; C80; C82) cages;1 which works as a n-dopant and in the incarcerated form it can be used as quantum bits in quantum computing2. Understanding of the position and binding pattern of the metal atom inside the cage is important as it controls the structural and electronic properties of the molecule. We found that Ce in Ce@C82 has a specific and unique binding site in C82-C2v and has a C2v symmetric structure; which is explained by the specific charge pattern of this binding site and the symmetry of the MO s that comply well with the Ce d orbital bonding.6 This six-membered ring binding site is also favored by La in La@C82. Each of the six-membered rings of C80-Ih fulfills this symmetry criterion and therefore a similar kind of binding site is expected for Ce in Ce2@C80. But; we observe a novel binding site for Ce in presence of an additional cerium atom; while La preserve its usual binding pattern in La2@C80 as in La@C82.7 We here discuss and analyze the reason for the preference of novel binding site of Ce atoms in C80-Ih by explaining the competitive binding nature of Ce-Ce and Ce-C. Surprisingly; Ce in Ce2@C78 unlike Ce2@C80 has its binding pattern as in Ce@C60 and in Ce@C82 (binding to a six-membered ring). We explain this variation in binding together with the nature of the charge transfer between the Ce atoms and the cage (C82 and C80). In addition; we explain experimental observations for Ce@C82 and Ce2@C80 from RESPES; IETS; STM/STS spectra by comparison with simulated properties

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