Population analysis and the effects of Gaussian basis set quality and quantum mechanical approach: main group through heavy element species.

Atomic charge and its distribution across molecules provide important insight into chemical behavior. Though there are many studies on various routes for the determination of atomic charge, there are few studies that examine the broader impact of basis set and quantum method used over many types of population analysis methods across the periodic table. Largely, such a study of population analysis has focused on main-group species. In this work, atomic charges were calculated using several population analysis methods including orbital-based methods (Mulliken, Löwdin, and Natural Population Analysis), volume-based methods (Atoms-in-Molecules (AIM) and Hirshfeld), and potential derived charges (CHELP, CHELPG, and Merz-Kollman). The impact of basis set and quantum mechanical method choices upon population analysis has been considered. The basis sets utilized include Pople (6-21G**, 6-31G**, 6-311G**) and Dunning (cc-pVnZ, aug-cc-pVnZ; n = D, T, Q, 5) basis sets for main group molecules. For the transition metal and heavy element species examined, relativistic forms of the correlation consistent basis sets were used. This is the first time the cc-pVnZ-DK3 and cc-pwCVnZ-DK3 basis sets have been examined with respect to their behavior across all levels of basis sets for atomic charges for an actinide. The quantum methods chosen include two density functional (PBE0 and B3LYP), Hartree-Fock, and second-order Møller-Plesset perturbation theory (MP2) approaches.

Interaction energies of CO2·amine complexes: effects of amine substituents.

To focus on the identification of potential alternative amine carbon capture compounds, CO(2) with methyl, silyl, and trifluoromethyl monosubstituted and disubstituted amine compounds were studied. Interaction energies of these CO(2)·amine complexes were determined via two methods: (a) an ab initio composite method, the correlation consistent composite approach (ccCA), to determine interaction energies and (b) density functional theories, B3LYP/aug-cc-pVTZ and B97D/aug-cc-pVTZ. Substituent effects on the interaction energies were examined by interchanging electron donating and electron withdrawing substituents on the amine compounds. The calculations suggested two different binding modes, hydrogen bonding and acid-base interactions, which arise from the modification of the amine substituents, echoing previous work by our group on modeling protein·CO(2) interactions. Recommendations have been noted for the development of improved amine scrubber complexes.

Comment on the paper "Extensive theoretical studies of a new energetic material: tetrazino-tetrazine-tetraoxide (TTTO)" by Xinli Song, Jicun Li, Hua Hou, and Baoshan Wang.

Discrepancies are noted in the implementation and presentation of the ccCA methodology in a previous publication, "Extensive Theoretical Studies of a New Energetic Material: Tetrazino-tetrazine-tetraoxide (TTTO)" by Xinli Song, Jicun Li, Hua Hou, and Baoshan Wang. The enthalpy of formation for TTTO has been re-evaluated using the correct implementation of the ccCA methodology, demonstrating the results to be comparable to those of other ab initio composite methods.

Highly energetic nitrogen species: reliable energetics via the correlation consistent Composite Approach (ccCA).

Gas-phase enthalpies of formation (ΔH(f(g))°) have been determined for 40 nitrogen-containing compounds at 298 K. Three ab initio composite methods have been compared in their abilities to quantitatively determine ΔH(f(g))°; the G3, G3(MP2), and correlation consistent Composite Approach (ccCA) methodologies. The ccCA method resulted in a mean absolute deviation (MAD) of 1.1 kcal mol(-1) when compared to available experimental values. The comparable G3(MP2) method resulted in a MAD of 1.8 kcal mol(-1), while the G3 method resulted in a MAD of 1.2 kcal mol(-1). As a result of their comparable accuracies, the ccCA and G3 methods have been utilized to predict the ΔH(f(g))° of five energetic but highly endothermic tetrazine-containing compounds with potential applications as insensitive high explosives.

CO2-formatics: how do proteins bind carbon dioxide?

The rising atmospheric concentration of CO(2) has motivated researchers to seek routes for improved utilization, increased mitigation, and enhanced sequestration of this greenhouse gas. Through a combination of bioinformatics, molecular modeling, and first-principles quantum mechanics the binding of carbon dioxide to proteins is analyzed. It is concluded that acid/base interactions are the principal chemical force by which CO(2) is bound inside proteins. With respect to regular secondary structural elements, beta-sheets show a marked preference for CO(2) binding compared to alpha-helices. The data also support the inference that while either or both oxygens of CO(2) are generally tightly bound in the protein environment, the carbon is much less "sequestered." First principles and more approximate modeling techniques are assessed for quantifying CO(2) binding thermodynamics.