where ε ∞ , ε 2/3 , and ε 1/3 are the fitted coefficients. We obtained the parametrizations of the energy, electronegativity, and hardness as a function of the helium cluster size using the following procedure: • Various helium cluster initial geometries for n ≤ 1000 were cut from the hexagonal closed packing (HCP) spherical cluster of 1002 atoms, optimized using the GFN-FF force field implemented in xTB software. HCPtype arrangement was chosen as a building pattern for clusters since solid helium can exist in this structure. For each of these He n clusters, structure optimization and harmonic frequency calculations were performed at the semi-empirical GFN2-xTB level of theory using the xTB software. • For these He n clusters, the single point energies (E(n)) were computed at the DLPNO-CCSD/aug-cc-pVDZ level of theory. IP and EA were computed using IP-EOM-DLPNO-CCSD/aug-cc-pVDZ, and EA-EOM-DLPNO-CCSD/aug-cc-pVDZ levels of theory, respectively. All these calculations were done using the ORCA 5 program package. • The resulting total energies (E tot (n) = E(n) + ZPVE), comprised of the zero-point vibrational energy (ZPVE) at the GFN2-xTB level of theory and the electronic energy (E(n)) at the DLPNO-CCSD/aug-cc-pVDZ level of theory, were fitted to the Equation . The resulting parameters were ε ∞ = 78.6531±0.0001 [eV], ε 2/3 = 13.8±0.6