Deep eutectic solvents (DESs) are promising candidates as alternate media for industrial gas sequestration processes, such as denitrification via NO adsorption. Here, quantum chemical methods are employed to characterize the NO solvation structure and adsorption mechanism in choline chloride DES with urea, methylurea, and thiourea hydrogen bond donors. Our results show that the solvation structure of NO in bulk choline chloride DES is determined by the type of the hydrogen bond donor present. Changing the structure of the hydrogen bond donor not only changes its NO coordination mechanism but also changes that between NO and the choline and chloride ions in the DES. By using an energy decomposition analysis scheme, we show that the principle forces stabilizing NO in these DES are dispersion and polarization interactions and, consequently, that NO adsorption is most favorable in the choline chloride-thiourea DES. These results highlight a potential route for the optimization of choline chloride DES for denitrification, by modulating the hydrogen bond donor structure.

The ability to accurately calculate relative energies of fullerenes is important in many areas of computational nanotechnology. Due to the large size of fullerenes, their relative energies cannot normally be calculated by means of high-level ab initio procedures, and therefore density functional theory (DFT) represents a cost-effective alternative. In an extensive benchmark study, we calculate the electronic energies of eight C60 isomers by means of the high-level G4(MP2) composite procedure. G4(MP2) isomerization energies span a wide range between 307.5-1074.0 kJ mol -1 . We use this benchmark data to assess the performance of DFT, double-hybrid DFT (DHDFT), and MP2-based ab initio methods. Surprisingly, functionals from the second and third rungs of Jacob's Ladder (i.e., GGA and meta-GGA functionals) significantly and systematically outperform hybrid and hybrid-meta-GGA functionals, which occupy higher rungs of Jacob's Ladder. In addition, DHDFT functionals do not offer a substantial improvement over meta-GGA functionals, with respect to isomerization energies. Overall, the best performing functionals with mean absolute deviations (MADs) below 15.0 kJ mol -1 are (MADs given in parenthesis) the GGA N12 (14.7); meta-GGAs M06-L (10.6), M11-L (10.8), MN15-L (11.9), and TPSS-D3BJ (12.8); and the DHDFT functionals B2T-PLYP (9.3), mPW2-PLYP (9.8), B2K-PLYP (12.1), and B2GP-PLYP (12.3 kJ mol -1 ). In light of these results, we recommend the use of meta-GGA functionals for the calculation of fullerene isomerization energies. Finally, we show that inclusion of very small percentages of exact Hartree-Fock exchange (3-5%) slightly improves the performance of the GGA and meta-GGA functionals. However, their performance rapidly deteriorates with the inclusion of larger percentages of exact Hartree-Fock exchange.

Accurate double-hybrid density functional theory and isodesmic-type reaction schemes are utilized to report accurate estimates of the heats of formation (Δ H) for all 24 isolated-pentagon-rule isomers of the third most abundant fullerene, C. Kinetic stabilities of these C isomers are also considered via C-C bond cleavage rates ( P) calculated using density functional theory. Our results show that the relative abundance of C fullerene isomers observed in arc discharge synthesis is the result of both thermochemical and kinetic factors. This provides timely insight regarding the characterization of several C isomers that have been obtained experimentally to date. For instance, the established assignments of C isomers of (using the Fowler-Manolopoulos numbering scheme) 22 [ D(IV)], 23 [ D(II)], 19 [ D], 24 [ D], 11 [ C(IV)], and 4 [ D(I)] are consistent with the relative Δ H and P values for these structures. However, our thermochemical and kinetic stabilities of C isomers 14, 15, and 16 indicate that the two experimentally isolated C isomers are 15 and 16, contrary to some previous assignments. Of the remaining isolated isomers of symmetry C and D, definitive assignment was not possible with consideration of only Δ H and P.

We present a systematic assessment of the density functional tight binding (DFTB) method for calculating heats of formation of fullerenes with isodesmic-type reaction schemes. We show that DFTB3-D/3ob can accurately predict Δ f H values of the 1812 structural isomers of C 60 , reproduce subtle trends in Δ f H values for 24 isolated pentagon rule (IPR) isomers of C 84 , and predict Δ f H values of giant fullerenes that are in effectively exact agreement with benchmark DSD-PBEP86/def2-QZVPP calculations. For fullerenes up to C 320 , DFTB Δ f H values are within 1.0 kJ mol −1 of DSD-PBEP86/def2-QZVPP values per carbon atom, and on a per carbon atom basis DFTB3-D/3ob yields exactly the same numerical trend of (Δ f H [per carbon] = 722n −0.72 + 5.2 kJ mol −1). DFTB3-D/3ob is therefore an accurate replacement for high-level DHDFT and composite thermochemical methods in predicting of thermochemical stabilities of giant fullerenes and analogous nanocarbon architectures.