Accuracy of density functional theory in the prediction of carbon dioxide adsorbent materials

Abstract

*Density functional theory (DFT) has become the computational method of choice for modeling and characterization of carbon dioxide adsorbents, a broad family of materials which at present are urgently sought after for environmental applications. The description of polar carbon dioxide (CO2) molecules in low-coordinated environments like surfaces and porous materials, however, may be challenging for local and semilocal DFT approximations. Here, we present a thorough computational study in which the accuracy of DFT methods in describing the interactions of CO2 with model alkali-earth-metal (AEM, Ca and Li) decorated carbon structures, namely anthracene (C14H10) molecules, is assessed. We find that gas-adsorption energies and equilibrium structures obtained with standard (i.e. LDA and GGA), hybrid (i.e. PBE0 and B3LYP) and van der Waals exchange-correlation functionals of DFT dramatically differ from results obtained with second-order Møller-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 wrong charge-transfer and electrostatic Coulomb interactions between CO2 and AEMdecorated anthracene molecules. Nevertheless, 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 (i.e. an extended two-dimensional material), hybrid exchange-correlation DFT and MP2 methods quantitatively provide similar results.

The role of density functional theory methods in the prediction of nanostructured gas-adsorbent materials

“…The origins of the observed hybrid DFT and MP2 numerical discrepancies (see Fig. 7c) are rationalized in terms of residual self-interaction errors [272]. The amount of charge transferred between the gas molecules and Ca-C 14 H 10 turns out to be the same when computed with either hybrid DFT or MP2 methods, and long-range dispersion interactions appear to be secondary in the present system (see Table 1 in work [272]).…”

“…7c) are rationalized in terms of residual self-interaction errors [272]. The amount of charge transferred between the gas molecules and Ca-C 14 H 10 turns out to be the same when computed with either hybrid DFT or MP2 methods, and long-range dispersion interactions appear to be secondary in the present system (see Table 1 in work [272]). Cazorla et al therefore conclude that the strength of the resulting electrostatic interactions, which are dominant, must be equal in the two compared cases.…”

“…The accuracy of standard and hybrid DFT functionals in describing the interactions of CO 2 molecules with Cadecorated graphene has been recently assessed by Cazorla et al [272]. In Cazorla's work, a comparative study between DFT and MP2 calculations is presented by following an original recipe: instead of adopting the customary strategy of steadily increasing the size of polyciclic aromatic hydrocarbon (PAH) molecules, the concentration of Ca dopants in anthracene (i.e., C 14 H 10 , a relatively small PAH) is tuned so as to mimic the partial density of electronic valence states in Ca-decorated graphene (see Fig.…”

“…Also, for justifying the subsequent generalization of the attained conclusions to extended materials [272]. Nevertheless, only few selected electronic features of the targeted system (e.g., partial density of electronic states around the Fermi energy level) can be reproduced at a time by playing with doping strategies, and probably only at a qualitative level.…”

“…Cazorla et al therefore conclude that the strength of the resulting electrostatic interactions, which are dominant, must be equal in the two compared cases. On the other side, LDA and PBE standard functionals overestimate the transfer of charge to the CO 2 molecule by 30 − 40% [272]. In light of those outcomes, the use of hybrid DFT functionals is recommended over that of local and semilocal approaches for investigation of the gas-uptake properties of AEMdecorated carbon GAM.…”