Translational eigenstates of He@C60 from four-dimensional ab initio potential energy surfaces interpolated using...

Area of Science:

• Quantum chemistry
• Materials science
• Computational physics

Background:

• Endofullerene systems, like 3He@C60, are of interest for studying quantum phenomena within confined spaces.
• Accurate potential energy surfaces (PES) are crucial for understanding the dynamics of guest atoms inside fullerene cages.

Purpose of the Study:

• To develop and utilize a four-dimensional potential energy surface (PES) for the 3He@C60 system.
• To evaluate and compare various electronic structure methods for their accuracy and efficiency in describing this system.
• To calculate the in-cage translational/vibrational eigenstates and fundamental frequencies.

Main Methods:

• A four-dimensional PES was constructed, incorporating He translational degrees of freedom and C60 cage radius.
• Gaussian Process Regression (GPR) was employed to interpolate the PES due to computational expense.
• Electronic structure methods, including MP2 and RPA@PBE, were compared.
• The nuclear Hamiltonian was diagonalized to obtain eigenstates.

Main Results:

• The degeneracy of harmonic oscillator energy levels was lifted due to anharmonicity and angular dependence in the potential.
• The fundamental frequency was calculated to be between 96 and 110 cm-1, varying with the electronic structure method.
• MP2 and RPA@PBE showed the best agreement with empirical potentials.
• GPR provided error bars on eigenstate energies of approximately ±1.5 cm-1.

Conclusions:

• Random Phase Approximation (RPA) is a computationally efficient and accurate alternative to MP2 for studying endofullerene systems.
• The developed PES and computational approach provide a reliable framework for future investigations of similar systems.