<i>A Priori</i> Theoretical Model for Discovery of Environmentally Sustainable Perfluorinated Compounds

Since SF₆ is the most potent greenhouse gas, the search for a viable alternative is taking on great urgency for several decades but without success. The demanding combination of performance, safety, and environmental properties for the new chemistry superior to SF₆ was thought to be nearly impossible to achieve. In contrast to the commonly used mixtures with two or three individual gases, a hybrid model has been proposed to create the new perfluorinated compounds with multiple unsaturated chemical bonds by means of full or partial integration of the parent molecules. A unique combination of a series of paradoxical properties that is high in dielectric strength and stability, low in boiling point, and significantly lower in global warming potential is achieved for the first time. The present <i>a priori</i> theoretical predictions shed new lights on the rational molecular design of the perfluorinated compounds and will greatly inspire experimental synthesis and field tests on the new chemistry for dielectric use

Double-Layered Composite Methods Extrapolating to Complete Basis-Set Limit for the Systems Involving More than Ten Heavy Atoms: Application to the Reaction of Heptafluoroisobutyronitrile with Hydroxyl Radical

Two versions of the double-layered composite methods, including the restricted open-shell model chemistry based on the complete basis set quadratic mode (DL-ROCBS-Q) and the extrapolated CBS limit of electronic energy on the basis of the coupled cluster with single, double, and noniterative triple excitations with the hierarchical sequence of the correlation-consistent basis sets (DL-RCCSD­(T)/CBS), were developed to calculate the energetic reaction routes for the systems involving 13/14 heavy atoms with good balance between efficiency and accuracy. Both models have been employed to investigate the oxidation reactions of heptafluoroisobutyronitrile ((CF₃)₂CFCN) with hydroxyl radical. The (CF₃)₂CFCN + OH reaction is dominated by the C–O addition/elimination routes as bifurcated into trans- and cis-conformations. Although the formation of isocyanic acid or hydrogen fluoride is highly exothermic, the major nascent product was predicted to be the less exoergic cyanic acid. Preference of the product channels could be tuned by the single water molecule in the presence of the H₂O–HO complex. The production of amide compound was found to be the most significant route accompanied by the OH regeneration. Moreover, the OH radical could be an efficient catalyst for the hydrolysis of (CF₃)₂CFCN. Implication of the current theoretical results in the chemistry of (CF₃)₂CFCN for both atmospheric sink and potential dielectric replacement gas was discussed

Molecular Dynamics Simulations of Ice Growth from Supercooled Water When Both Electric and Magnetic Fields Are Applied

TIP4P/2005 force-field-based classical molecular dynamics simulations were employed to investigate the microscopic mechanism for the ice growth from supercooled water when the external electric (0–10⁹ V/m) and magnetic fields (0–10 T) are applied simultaneously. Using the direct coexistence ice/water interface, the anisotropic effect of electric and magnetic fields on the basal, primary prismatic, and the secondary prismatic planes of ice Ih has been calculated. It was revealed for the first time that the solvation shells of supercooled water could be affected by the cooperative electric and magnetic fields. Meanwhile, the self-diffusion coefficient is lowered, and the shear viscosity increases considerably. The critical electric and magnetic fields to accelerate ice growth on the prismatic plane are fairly low (ca. 10⁶ V/m and 0.01 T). In contrast, the basal plane is hardly affected unless the fields increase to the order 10⁹ V/m and 10 T. Rotational dynamics of water molecules might play an important role in ice growth with the applied external fields. Density functional theory with the triple numerical all-electron basis set was used to reveal the electronic structures of the basal and primary prismatic planes of ice Ih with respect to the anisotropic effect of ice growth

Theoretical Study of the Adsorption/Dissociation Reactions of Formic Acid on the α‑Al₂O₃(0001) Surface

Formic acid was used as the model of lauric acid to investigate the microscopic mechanism of the anti-icing behavior and was checked to find out if it can be catalyzed to produce H₂ for fuel cells by the α-Al₂O₃(0001) 2 × 2 supercell slab model. The density functional theory with the all-electron double numerical polarized basis sets was employed. The results show that when it involves the carboxyl O and hydroxyl H atom the 1,2-dissociated adsorbate is the most stable intermediate on the dry Al₂O₃(0001) surface and is energetic barrier free to form the fairly stable ROCO- and HO-covered surface with the binding energy of 59.5 kcal/mol, and this dissociation mode has the lowest energy barrier of 14.9 kcal/mol to form the HOCO- and H₂O-covered surface after the surface is fully hydroxylated. The energetic barrier of the HCOOH dehydrogenation and dehydration reactions on the alumina surface decreased considerably from 65.3 to 30.6 kcal/mol and from 62.1 to 26.8 kcal/mol, respectively, in comparison with the gaseous decomposition. The dissociated configuration of lauric acid was tested, and it was found that it dissociated with free energy barrier through 1,2-hydrogen migration into the C₁₁H₂₃OCO- and HO-covered surface with a binding energy of 60.7 kcal/mol. The present theoretical work is useful to gain some new insights on the microscopic interaction mechanism of the superhydrophobic alumina surface fabrication procedure and on the heterogeneous catalysis reactions of the H₂ production

Electronic Structures and OH-Induced Atmospheric Degradation of CF₃NSF₂: A Potential Green Dielectric Replacement for SF₆

Electronic structures of [(trifluoromethyl)­imino]sulfur difluoride (CF₃NSF₂) and degradation mechanisms by hydroxyl radical have been investigated using density functional theory (M06-2X), the complete basis set quadratic CBS-Q, and the explicitly correlated coupled-cluster methods [CCSD­(T)-F12]. The d-function augmented correlation-consistent basis sets including triple- and quadruple-ξ were employed for the sulfur-containing species. It was found that CF₃NSF₂ exists as two conformations connected by the internal rotation of CF₃ around the central NS bond. The distorted <i>syn</i> conformer is more stable than the symmetrical <i>anti</i> conformer. The nitrogen–sulfur link in CF₃NSF₂ was revealed to be predominantly ionic CF₃N^––⁺SF₂ in structure rather than the conventional NS double bond on the basis of natural bond orbital analysis. OH radical prefers to attach on the S atom of CF₃NSF₂ along the opposite direction of the SF bond via a nucleophilic addition mechanism with a barrier of 2.9 kcal/mol whereas the ON association pathway is negligible. Although many product channels are thermodynamically favorable, none of them is kinetically accessible because of the significant barriers along the reaction routes. However, the degradation of CF₃NSF₂ by OH can be accelerated considerably in the presence of a single water molecule, which acts as a bridge for the consecutive proton migration within the floppy cyclic geometries. The half-life of CF₃NSF₂ was estimated to be 2.5 year, and the final products are exclusively CF₃NH and SF₂O. Theoretical calculation supports that CF₃NSF₂ is an environment-friendly green gas. It is worthy of testing its dielectric properties to replace SF₆ for practical use