Behavior of HF and (HF)(2) inside a fullerene cage: An in silico study using different density functionals

An in silico study on the properties of HF and its dimer inside C-60 using density functional theory (DFT) based approaches is presented. For this purpose, 10 different DFT functionals following Jacob's Ladder have been chosen. The geometrical parameters such as bond length and bond angle, of the molecules and their dipole moment have been computed. Two types of orientations, namely, L-shaped and anti-parallel of (HF)(2) inside C-60 are considered, the latter with an extremely short hydrogen bond. HF bond lengths are elongated upon encapsulation in comparison to its free state analogue. The calculated value of stabilization energy of HF@C-60 is found to be functional dependent, whereas, (HF)(2)@C-60 is thermodynamically unstable for all the functionals. The kinetic stability of (HF)(2)@C-60 is assessed using the atom-centered density matrix propagation (ADMP) simulation at 300 K temperature. The red shift in HF stretching frequencies is noticed in all cases. Non-covalent index (NCI) analysis revealed non-covalent interactions between HF dimer and the C-60 cage. Energy decomposition analysis (EDA) showed a high value for the repulsive & UDelta;E-pauli which makes the (HF)(2)@C-60 system unstable except for the functional BP86-D3 of GGA family. Furthermore, the quantum theory of atoms in molecules (QTAIM) analysis is performed and it confirmed the presence of (3, -1) bond critical point along the hydrogen bond region of the L-shaped (HF)(2)@C-60.