  We have performed a thorough computational study to assess the accuracy of
density functional theory (DFT) methods in describing the interactions of CO2
with model alkali-earth-metal (AEM, Ca and Li) decorated carbon structures,
namely anthracene (C14H10) molecules. We find that gas-adsorption energy and
equilibrium structure results obtained with both standard (i.e. LDA and GGA)
and hybrid (i.e. PBE0 and B3LYP) exchange-correlation functionals of DFT differ
significantly from results obtained with second-order Moller-Plesset
perturbation theory (MP2), an accurate computational quantum chemistry method.
The major disagreements found can be mostly rationalized in terms of electron
correlation errors that lead to inaccurate charge transfers and electrostatic
Coulomb interactions between the molecules. Interestingly, we show that when
the concentration of AEM atoms in anthracene is tuned to resemble as closely as
possible to the electronic structure of AEM-decorated graphene, hybrid
exchange-correlation DFT and MP2 methods provide quantitatively similar
results. We discuss the implications of our work in modeling and
characterization of currently sought carbon capture and sequestration
materials.
