Theoretical study on the smallest endohedral metallofullerenes: TM@C₂₀ (TM = Ce and Gd)

Abstract

ABSTRACT:The structure, electronic property, and infrared spectroscopy of endohedral metallofullerenes TM@C 20 (TM ¼ Ce and Gd) have been systematically investigated with the aid of the hybrid DFT-B3LYP functional. It is found that in the endohedral metallofullerenes the average CAC bond lengths are obvious longer than those of empty cage. The frontier orbital analyses show that the endohedral metallofullerene Gd@C 20 has the high-thermodynamic stability. Natural population analysis also tells us that only in the Ce@C 20 , the Ce atom acts as an electron acceptor with the negative charges, and the 4f orbitals of Ce and Gd atoms have a significant contribution in the formation of chemical bonding. Additionally, the analyses of harmonic vibrational frequencies reveal that when the TM atoms are encapsulated into the C 20 cage, the strongest absorption peaks are characterized by a mixture of TMÀC bending and CAC stretching vibrations.

Ab initio infrared vibrational modes for neutral and charged small fullerenes (C 20 , C 24 , C 26 , C 28 , C 30 and C 60 )

“…The calculated spectrum for neutral C 20 (figure 2) agrees well with previous literature data (B3LYP with the 6-31++G basis [38] and 6-31G(d) basis [39]), featuring two primary peaks at 1324 cm −1 (7.55 µm) and 769 cm −1 (13.00 µm). Peaks in these two spectral regions are seen in many of the small fullerene spectra discussed below.…”

Optical Properties and Quasiparticle Band Gaps of Transition-Metal Atoms Encapsulated by Silicon Cages

“…25,26 Recently, theoretical predictions of metallofullerenes containing transition metal atoms have indicated that their electronic and optical properties can be properly tuned. 27,28 All these features also deserve to be carefully evaluated in the context of the silicon cage clusters containing transition metal atoms.…”

Encapsulation of an f-block metal atom/ion to enhance the stability of C20with the Ihsymmetry

“…The combination of DFT with small-core RECPs has been shown to provide good results for lanthanide and actinide systems at a reasonable computational cost. 47,53,54 To understand the charge reorganization due to the formation of the M@C 20 cluster from M and C 20 species, the partial atomic charges were calculated using the Lo ¨wdin and Hirshfeld schemes as implemented in the Multiwfn program. 64 The Voronoi deformation density (VDD) 65 charges were calculated from the flow of electron density to or from a certain atom or a fragment due to the bond formation, thus evaluating the charge rearrangements due to the formation of the complex between the lanthanide or actinide atom/ ion and C 20 fragments.…”

“…Recently, neutral Ce@C 20 and Gd@C 20 clusters and 3d transition metal atom encapsulated C 20 clusters have been studied theoretically. [47][48][49] These clusters have C 2h symmetry, which is much lower than the I h symmetry, probably because of the absence of a magic number electronic configuration. Recently, Manna et al theoretically predicted a new series of M@C 20 34 (M = Pr À , Pa À , Nd, U, Pm + , Np + , Sm 2+ , Pu 2+ , Eu 3+ , Am 3+ , Gd 4+ , and Cm 4+ ) clusters, a 26-electron system with the I h symmetry, and explained their enhanced stability from the aspect of a large HOMO-LUMO energy gap, large binding energy, etc.…”