Physical Chemistry

Local Energy Decomposition Analysis and Molecular Properties of Encapsulated Methane in Fullerene ([email protected])

Aleksander Jaworski Stockholm University
,

Abstract

Methane has been successfully encapsulated within cages of C60 fullerene, and it is an appropriate model system to study confinement effects. Its chemistry and physics is also relevant for theoretical model descriptions. Here we provided insights into intermolecular interactions and predicted spectroscopic responses of the CH4@C60 complex and compared with results from other methods and with literature data. Local energy decomposition analysis (LED) within the domain-based local pair natural orbital coupled cluster singles, doubles, and perturbative triples (DLPNO-CCSD(T)) framework was used, and an efficient protocol for studies of endohedral complexes of fullerenes is proposed. This approach allowed us to assess energies in relation to electronic and geometric preparation, electrostatics, exchange, and London dispersion for the CH4@C60 endohedral complex. The calculated stabilization energy of CH4 inside the C60 fullerene was −13.5 kcal/mol and its magnitude was significantly larger than the latent heat of evaporation of CH4. Evaluation of vibrational frequencies and polarizabilities of the CH4@C60 complex revealed that the infrared (IR) and Raman bands of the endohedral CH4 were essentially “silent” due to dielectric screening effect of the C60, which acted as a molecular Faraday cage. Absorption spectra in the UV-Vis domain and ionization potentials of the C60 and CH4@C60 were predicted. They were almost identical. The calculated 1H/13C NMR shifts and spin-spin coupling constants were in very good agreement with experimental data. In addition, reference DLPNO-CCSD(T) interaction energies for complexes with noble gases
([email protected] ; Ng = He, Ne, Ar, Kr) were calculated. The values were compared with those derived from supermolecular MP2/SCS-MP2 calculations and estimates with London-type formulas by Pyykkö and coworkers [Phys. Chem. Chem. Phys., 2010, 12, 6187-6203], and with values derived from
DFT-based symmetry-adapted perturbation theory (DFT SAPT) by Hesselmann & Korona [Phys. Chem. Chem. Phys., 2011, 13, 732-743]. Selected points at the potential energy surface of the endohedral He2@C60 trimer were considered. In contrast to previous theoretical attempts with the DFT/MP2/SCS-MP2/DFT-SAPT methods, our calculations at the DLPNO-CCSD(T) level of theory predicted the He2@C60 trimer to be thermodynamically stable, which is in agreement with experimental observations.

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Supplementary material

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