Silicon- and carbon-based anode materials: Quantum-chemical modeling

With the aim of searching for promising anode materials for lithium-ion batteries, we performed quantum-chemical modeling of the structure, stability, and electronic properties of silicon-coated carbon nanotubes, silicon rods, and silicon carbide fibers by the density functional theory method including gradient correction and periodic boundary conditions. It has been demonstrated that nanotubes poorly hold silicon, whereas silicon firmly adheres to the SiC surface. Silicon rods are more favorable than clusters and have the stability close to that of the crystal. The band gap in the rods is close to zero. Silicon carbide can be transformed into a conductor by doping with nitrogen.     

Optical properties of oxygen vacancies in germanium oxides: quantum chemical modeling of photoexcitation and photoluminescence

Photoabsorption and photoluminescence properties of single and double oxygen vacancy (OV and DOV) defects in quartz-like germanium oxide have been investigated by high-level ab initio calculations. It has been found that photoabsorption for these systems occurs at lower energies as compared to the analogous defects in SiO(2). For OV, the lowest electronic excitations with high oscillator strengths have energies of 6.7-7.0 eV, whereas for DOV, the lowest-energy photoabsorption band is calculated to be in the range of 5.5-5.9 eV. Significant geometry relaxation and large Stokes shift are inherent for these excited states and, as a result, their photoluminescence bands are predicted to peak at 3.1-3.3 eV for OV and at 2.6 eV for DOV. The double oxygen vacancy is suggested to be the most suitable candidate for generating bright blue photoluminescence observed experimentally for substoichiometric quartz-like GeO(2) nanowires, as the calculated optical properties of DOV are in close agreement with the features found in experiment.     

Nonaqueous LiNafion-based polymeric electrolyte: quantum-chemical modeling

In the framework of the search for promising electrolytes for lithium-ion batteries, quantumchemical modeling of the structure, stability, and electronic properties of membranes based on LiNafion. nDMSO, n = 0–16) has been performed by the density functional theory method with inclusion of gradient correction and periodic conditions (PBE/PAW). Inasmuch as the key factor that determines the ionic conductivity is the degree of swelling of LiNafion in DMSO (according to calculations, for n = 8, the degree of swelling is close to 500%, and for n = 16, it is close to 700% by volume), similar membranes can be good candidates from the viewpoint of lithium ion transport (with barriers of 0.2–0.3 eV, which depend on n).     

Quantum-chemical modeling of the dissociative adsorption of molecular hydrogen onto the tin dioxide surface

The hydrogen adsorption, dissociation, and migration on the tin dioxide surface have been modeled by the density functional theory method within the generalized gradient approximation (GGA) under periodic conditions using a projector-augmented plane-wave (PAW) basis set with a pseudopotential. It has been demonstrated that dissociative chemisorption onto the tin dioxide surface depends on the adsorption site and the surface structure and that there are places on the surface where dissociation can occur with a low barrier of 0.1–0.2 eV to yield a primary isomer in which one of the hydrogen atoms is bound to the tin atom and the other, to an oxygen atom; the second dissociation even at the same place is possible only if the primary isomer overcomes a barrier of ∼1 eV and transforms to the secondary isomer with two O-H bonds.     

Behavior of molecular hydrogen on the platinum crystal surface: Quantum-chemical modeling

The interaction of molecular hydrogen with the (111), (110), and (100) surfaces of the platinum crystal has been modeled by the density functional theory method within the generalized gradient approximation (GGA). The (100) surface is the least energetically favorable one, while the (111) and (110) surfaces are close in energy. The hydrogen molecule is attached to all three types of surfaces without a barrier. The largest decrease in energy is realized for the (100) surface. The bidentate coordination of hydrogen atoms is typical of the (100) and (110) surfaces, and the tridentate coordination is characteristic of the (111) surface. The H atoms can migrate over the crystal surface, overcoming moderate potential barriers of ??0.1?C0.2 eV; however, over the (110) surface, migration is possible only along the ridges. The maximal number of attached atoms per surface atom is close to unity for the (111) or (110) surface and to 1.67 for the (100) surface.     

Platinum nanoparticles on different types of titanium dioxide surface: A quantum-chemical modeling

The interaction of a Pt₂₉ nanoparticle with pristine and reduced TiO₂ (110), (100), (101), and (100) surfaces in the rutile and anatase modifications has been modeled by the density functional theory method within the generalized gradient approximation (GGA). It has been demonstrated that the interaction energy of platinum particles with stoichiometric surfaces of titanium dioxide crystals is noticeably lower than for tin dioxide crystals. Like for SnO₂, the reduction of the surface leads in some cases to a significant increase in the energy of interaction with platinum. The reoxidation of such structures should result in platinum fixation on the surface.     

Quantum-chemical calculations of electronic structures and molecular properties within the framework of approximate schemes of zero differential overlap

Journal of Structural Chemistry -     

Nonempirical calculations of potential energy-surfaces of the intramolecular rearrangement of LiBX+ and LiA1X+ ions

Institute of New Chemical Problems, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 3, pp. 19–23, May–June, 1989.