Figure 2 . DFT adsorption structures. a) Top and side views of
gas-MPBCP system. b) NBO donor and acceptor orbitals responsible for
intermolecular interactions. The adsorption energy
(Eads ) are expressed in kcal/mol calculated with
the PBE0-D3/def2-TZVP method. Color code for spheres: dark gray (C);
blue (N); yellow (H); red (O).