Interaction between graphene and SiO2 surface

With first-principles DFT calculations, the interaction between graphene and SiO2 surface has been analyzed by constructing the different configurations based on {\alpha}-quartz and cristobalite structures. The single layer graphene can stay stably on SiO2 surface is explained based on the general consideration of configuration structures of SiO2 surface. It is also found that the oxygen defect in SiO2 surface can shift the Fermi level of graphene down which opens out the mechanism of hole-doping effect of graphene absorbed on SiO2 surface observed in experiments.Comment: 17 pages, 7 figure

Assessment of the Heat Capacity by Thermodynamic Approach Based on Density Functional Theory Calculations

The theoretical aspects of the thermodynamic calculation of the Gibbs energy and heat capacity of a crystalline system within the frame of the Density Functional Theory (DFT) are introduced in the present chapter. Various approximations of phonon motion (harmonic, quasiharmonic, and anharmonic) and their effects on the thermodynamic properties are discussed. The theoretical basis of the thermodynamic approach of the heat capacity of crystals for given thermodynamic conditions is presented, having as example six polymorphs of the magnesium hydrides

Hydrogen bond network topology in liquid water and methanol: a graph theory approach

Networks are increasingly recognized as important building blocks of various systems in nature and society. Water is known to possess an extended hydrogen bond network, in which the individual bonds are broken in the sub-picosecond range and still the network structure remains intact. We investigated and compared the topological properties of liquid water and methanol at various temperatures using concepts derived within the framework of graph and network theory (neighbour number and cycle size distribution, the distribution of local cyclic and local bonding coefficients, Laplacian spectra of the network, inverse participation ratio distribution of the eigenvalues and average localization distribution of a node) and compared them to small world and Erdős–Rényi random networks. Various characteristic properties (e.g. the local cyclic and bonding coefficients) of the network in liquid water could be reproduced by small world and/or Erdős–Rényi networks, but the ring size distribution of water is unique and none of the studied graph models could describe it. Using the inverse participation ratio of the Laplacian eigenvectors we characterized the network inhomogeneities found in water and showed that similar phenomena can be observed in Erdős–Rényi and small world graphs. We demonstrated that the topological properties of the hydrogen bond network found in liquid water systematically change with the temperature and that increasing temperature leads to a broader ring size distribution. We applied the studied topological indices to the network of water molecules with four hydrogen bonds, and showed that at low temperature (250 K) these molecules form a percolated or nearly-percolated network, while at ambient or high temperatures only small clusters of four-hydrogen bonded water molecules exist

Mathematical Chemistry Approaches for Computer-Aid Design of Free-Shaped Structures in Architecture and Construction Engineering

The use of computers in architecture and construction engineering simplifies and automatize many manual operations, especially in the case of curved surfaces such as shell structures. Moreover, it allows fast screening and characterization of many technical solutions through computer-solving equations and the verification of buildings and metallic structures stabilities in different weather and seismic conditions. In parallel, significant efforts have been made to characterize and explore carbon-based nanosystems. Important mathematical concepts and methods were developed for the description of such structures in the frame of mathematical chemistry. Because the lattice topology of shell structures in architecture and nanosystems in chemistry are similar, it is possible to transfer well-established theoretical concepts and knowledge of using nanosystems to the design of shell structures. The topologies of the nanosystems are characterized by lower densities of edges per node offering better solutions for curved surfaces than the typical grids used in architecture. As far as we know, no such connections between the topologies of nanosystems and shell structures have been established before. This transfer would be helpful for increased accuracy and speed in finding the best technical solutions for the building’s design. In this paper, we identify and propose for the design of the shell structures several mathematical approaches developed for atomistic systems

Interactions of methane, ethane and pentane with the (110C) surface of γ−alumina

Journal of Molecular Catalysis A: Chemical, 275(1-2): pp. 63-71.Adsorptions of methane, ethane and pentane on the γ-alumina (110C) surface are investigated with semi-empirical (PM3) cluster calculations. It is found that the abstraction of an H atom accompanied by the formation of a C-O bond is the most favorable reaction for methane on the alumina surface. For ethane- and pentane-alumina interactions, the abstraction of two H atoms accompanied by the formation of an alkene is the most favorable reaction. The surface Al atoms help to promote the reactions, but are not directly involved in the bond formation

Theoretical study of the reaction of LiBH4 with MgH2 in presence of carbon substrate

In this work we design some atomic scale simulation methods as investigative tools in the study of the formation of compounds for the reversible storage of hydrogen in bulk materials. It was verified that the reaction between the LiBH 4 and MgH 2 is energetically favored for temperatures above 280 K and that this system can be used in the hydrogen storage and the fuel cell application. To identify the reaction mechanism at the interface of LiBH 4 , MgH 2 and carbon layers we did some Molecular Dynamics simulations and QM/MM calculations. The results show that the layers of ions formed at the interface with the graphite may assure the right arrangement of the atoms to start the formation of the crystals. Moreover, the presence of the hexagonal layers of graphite may play a role as a pattern template for the layers of boron atoms in the MgB 2 lattice

Interactions of methane, ethane and pentane with the (110C) surface of gamma-alumina

Adsorptions of methane, ethane and pentane on the gamma-alumina (110C) surface are investigated with semi-empirical (PM3) cluster calculations. It is found that the abstraction of an H atom accompanied by the formation of a C-O bond is the most favorable reaction for methane on the alumina surface. For ethane- and pentane-alumina interactions, the abstraction of two H atoms accompanied by the formation of an alkene is the most favorable reaction. The surface Al atoms help to promote the reactions, but are not directly involved in the bond formation. (c) 2007 Elsevier B.V. All rights reserved

Magnetic anisotropy of ultrathin Pd4Co(111) film by first-principles calculations

The Pd–Co alloy is a suitable candidate for the perpendicular magnetic recording and related applications. However, no research is available to clarify influences of local structures on the magnetic anisotropy of the Pd–Co alloy. Therefore, in this work, we studied the effects of Co arrangement on the magnetic anisotropy of ultrathin Pd4Co(111) film with 20% Co content by using the density functional theory calculations. We found that a Co monolayer in the surface layer of the ultrathin film offers a large in-plane magnetic anisotropy while the Co atoms mixed inside the Pd matrix exhibit the perpendicular magnetic anisotropy. Notably, a Co monolayer beneath the surface layer of the Pd matrix maximizes the perpendicular magnetic anisotropy up to 1.85 erg/cm2. Electronic properties were also analyzed to clarify the magnetic anisotropy of the ultrathin film. Keywords: Magnetic recording, Magnetic anisotropy, Density functional theory, Electronic structure properties, Ultrathin fil

Monte Carlo Simulations of the Magnetic Behavior, Ordering Temperature and Magnetocaloric Effects in 1D, 2D and 3D Ferrimagnetic Systems

As for the systematic investigations of magnetic behaviors and its related properties, computer simulations in extended quantum spin networks have been performed in good conditions via the generalized Ising model using the Monte Carlo-Metropolis algorithm with proven efficiencies. The present work, starting from a real magnetic system, provides detailed insights into the finite size effects and the ferrimagnetic properties in various 1D, 2D and 3D geometries such as the magnetic moment, ordering temperature, and magnetocaloric effects with the different values of spins localized on the different coordinated sites

Effects of Co Content in Pd-Skin/PdCo Alloys for Oxygen Reduction Reaction: Density Functional Theory Predictions

Improving the slow kinetics of the oxygen reduction reaction (ORR) on the cathode of the proton exchange membrane fuel cells to achieve the performance at a practical level is an important task. PdCo alloys appeared as a promising electrocatalyst. Much attention has been devoted to the study of the effects of the Co content on the ORR activity of PdCo films and PdCo/C nanoparticles where the Co atoms can be at the topmost surface layer. While Pd-skin/PdCo alloys with the topmost layer formed only by Pd have been proved to provide a very high ORR activity and high durability, no researches are available in the literature for the effects of the Co content on the ORR activity of Pd-skin/PdCo alloys. Hence, the effects of the Co content on the ORR activity of Pd-skin/PdCo alloys are clarified in this work by using the density functional theory calculations and Nørskov’s thermodynamic model. Our results predicted that the ORR activity increases monotonically with the increase of the Co content. This behavior is particularly different compared to the Volcano behavior previously obtained in the literature for PdCo films and PdCo/C nanoparticles