In this work, geometries, stabilities and electronic properties of carbon monoxide (CO) molecule as an adsorbent on simple carbon nanotube (CNT) and N, B, S-doped carbon nanotubes (NCNT, BCNT and SCNT) with parallel and perpendicular configurations are fully considered using ONIOM, natural bond orbital (NBO), and quantum theory of atom in molecule (QTAIM) calculations. The adsorption energies (Ead) demonstrate that CO molecule could be adsorbed on the surface of the simple carbon nanotube with parallel configuration (CNT-p) and N-doped carbon nanotube with perpendicular configuration (NCNT-d) in exothermic process. QTAIM calculations are showed the close-shell (non-covalent) interactions between CO molecule and CNT or N, B, S-doped CNTs. Also, the energy gap (Eg) values between the highest occupied molecular orbital and the lowest unoccupied molecular orbital are calculated. In accordance to the results of energy gap, simple and N-doped carbon nanotubes could be used as CO-sensors.
The presence of long abandoned, hexagonal omega (ω) phase in steel samples is recently gaining momentum on account of accurate transmission electron microscopy (TEM) measurements. The formation and stabilization of this metastable phase down to room temperature is attributed to the combined effect of factors such as accelerated cooling, special atomic constraints at twin boundaries, and the enrichment of solute elements such as Al, Mn, Si, C, and Cr in the nanometer sized regimes. Here, we present a density functional theory (DFT) study of the effect of the above alloying elements in ω-Fe and confirm the predictions using high resolution TEM observations of the structure of an experimental steel at high magnifications. It is found that the FM and ++- spin states are the most stable for a primitive cell of ω-Fe. The density of states calculations show that the d band occupancy of ω-Fe is changing in presence of the alloying elements, and this in turn will affect the cohesive energy. Further, the dynamical stability analysis from phonon band structure reveals that only ω-Fe with substitutional C exhibits thermodynamic stability. This is in line with experimental indications that the stabilization of ω-phase in ferritic/martensitic steels occurs due to the presence of special symmetry constraints at grain boundaries
Motivated by the particularly short metal-metal distance that has been predicted for the D3h [BeH3Be]+ cation, comparable to those anticipated for triple bonds, we investigate the nature of the bonding interactions in the D3h [MH3M]+ cations (M = Be, Mg). CCSD(T)/cc pVQZ calculations are used to determine optimized geometries for all of the various species, including those ‘capped’ by He or Ne atoms (as proxies for an inert gas matrix). The primary tools that are then used to investigate the nature of the chemical bonding are spin-coupled generalized valence bond calculations and the analysis of localized natural orbitals and of domain-averaged Fermi holes. The various results for all of the systems considered indicate the presence of highly polar three-centre two-electron M−H−M bonding character instead of any significant direct metal-metal bonding.
Building on a previous work, pseudopotential sets are developed and tested for a variety of \(sp^2\) and \(sp^3\) carbon fragments. These fragments contain only one or two explicit protons and electrons, and make use of non-atom-centred potentials. They are tested with Density Functional Theory calculations in a selection of chemical environments in which several physical characteristics, including orbital and first ionisation energies, are found to be well-reproduced. They are then employed in the reproduction of molecular absorption spectra for large organic molecules and carbon allotropes, and are found to recreate both absorption and ECD spectra to a high accuracy. They are also found significantly to increase the computational efficiency of TDDFT calculations in which they are used.
We have developed a new database of structures and bond energies of 45 noble-gas containing molecules. The structures were calculated by CCSD(T)/aug-cc-pVTZ methods and the bond energies were obtained using CCSD(T)/CBS (complete basis set) method. Many wavefunction-based and density functional theory methods have been benchmarked against the 45 accurate bond energies. Our result showed that the MPW1B95, B2GP-PLYP, and DSD-BLYP functionals with the aug-cc-pVTZ basis set excel on predicting the bond energies of the noble-gas molecules with MUEs (mean unsigned errors) of 1.5-1.9 kcal/mol. When combinations of Dunning’s basis sets are used, the MPW1B95, MPW1PW91, and B2GP-PLYP functional give significantly lower MUEs of 1.1-1.3 kcal/mol. Doubly hybrid methods using B2GP-PLYP and DSD-BLYP functionals and MP2 calculation also provide satisfactory accuracy with MUEs of 1.3-1.4 kcal/mol. If the noble-gas bond energies and the total atomization energies of a group of 109 main-group molecules are considered at the same time, the MPW1B95/aug-cc-pVTZ single-level method (MUE = 2.7 kcal/mol) and the B2GP-PLYP functional with combinations of basis sets (MUEs = 1.8 kcal/mol) give the overall best result.
Skin sensitization occurs when an exogenous chemical substance forms a covalent adduct with a dermal protein electrophile or nucleophile. This instigates an immune response which leads to inflammation. The local lymph node assay (LLNA) is an in-vivo model used in the assessment of relative skin sensitizing potency of chemicals. The method is time consuming and expensive, as well as poses ethical questions given that a number of mice must be sacrificed for each compound assessed. In this work we investigate the use of an inexpensive, rapid and ethical method to predict the skin sensitization potential of Schiff base chemicals. We employ quantum chemical methods to rationalize the sensitization potential of 22 compounds with a diverse range of activities. To this end we have evaluated the mechanistic profile associated with this type of reaction using gas-phase models. We subsequently use the predicted rate determining barriers and key physico-chemical parameters (such as logP) to establish SAR guidelines to predict the skin sensitization potential for new chemicals. We find that the predicted rate determining barriers for aldehydes, ketone and 1,2 and 1,3 diones generally decrease in the given order, which concurs with the overall trends in sensitization. We find that lipophilicity also plays a role, with those chemicals displaying both low barriers to reaction, and lower lipophilicity (i.e. diones), being more likely to display undesirable skin sensitization effects. These findings are in line with experimental based observations in the literature and point to the value 3D quantum chemical simulations can play in the combination of approaches used to estimate skin sensitization potential of chemicals.