Faculty of Physics - University of Bucharest

UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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2026-06-11 23:58

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Conference: Bucharest University Faculty of Physics 2026 Meeting

Section: Atomic and Molecular Physics. Astrophysics. Applications. Optics, Spectroscopy, Plasma and Lasers

Title:

Stability anomalies and magic numbers of hydrogen doped yttrium based endohedral metallofullerenes

Authors:

Aniszia-Stefania VAJDA (1), Leonard GEBAC (1), Vasile BERCU (1)

Affiliation:

1) Faculty of Physics, University of Bucharest

E-mail

aniszia.vajda@gmail.com

Keywords:

Endohedral metallofullerenes, nano-confinement, hydrogen storage, DFT

Abstract:

Endohedral metallofullerenes represent a unique class of carbon-based nanostructures with promising applications in molecular storage, quantum computing, and optoelectronic devices. This research analyzes the thermodynamic viability of utilizing a yttrium-doped endohedral fullerene (Y@C_{60}) for molecular hydrogen storage, with the long-term objective of evaluating whether nano-confinement can induce the physical and chemical compression required for high-temperature hydrogen metallization and subsequent superconductivity. To unify the concepts of hydride-based chemical pre-compression and nanotube physical confinement, spin-unrestricted Density Functional Theory (UDFT) calculations were performed to simulate the sequential loading of n=1 to 10 hydrogen molecules inside a Y@C_{60} cage. Thermodynamic stability was evaluated using incremental binding energies (dE) and second-order finite energy differentials ($Delta^2E$). The calculations revealed a critical exothermic energy minimum at n=2 (dE = -0.0056 eV), beyond which repulsive forces turn the loading process strictly endothermic at n=3 (dE = +0.2419 eV). The plot of the second-order energy differential ($Delta^2 E$) provides a direct measure of relative stability, displaying two prominent local minima at n=4 and n=9. Mathematically, these negative troughs signify points where the total energy exceeds the average of the adjacent states ($npm1$). Tying these minima back to the incremental energy graph (dE), they correspond perfectly to the onset of severe thermodynamic resistance, where forcing an additional molecule into the complex triggers a massive energy penalty (a jump to +1.37 eV at n=4 and a maximum of +4.61 eV at n=9). While Y@C_{60} should be dismissed as a practical gas carrier, it could represent a viable model for exploring low-pressure hydrogen metallization pathways via nano-confinement.