Quantum chemical modeling of the structure and properties of SnO2 nanoclusters

By the method of density functional theory with exchange-correlation functional B3LYP and basis set 3‑21G (d), the structural and energy characteristics have been considered of the molecular models of SnO2 nanoclusters of different size and composition with the number of Sn atoms from 1 to 10. Incompletely coordinated surface tin atoms were terminated by hydroxyl groups. It has been shown that the Sn–O bond length in nanoclusters does not depend on the cluster size and on the coordination number of Sn atoms, but is determined by the coordination type of neighboring oxygen atoms. Namely, the bond length Sn–O(3) (@ 2.10 Å) is greater than that of Sn–O (2) (@ 1.98 Å). The calculated values of Sn–O (3) bond lengths agree well with the experimental ones for crystalline SnO 2 samples (2.05 Å). The theoretically calculated width of the energy gap decreases naturally with increasing cluster size (from 6.14 to 3.46 eV) and approaches the experimental value of the band gap of the SnO 2 crystal (3.6 eV). The principle of additivity was used to analyze the energy characteristics of the considered models and to estimate the corresponding values for a cassiterite crystal. According to this principle, a molecular model can be represented as a set of atoms or atomic groups of several types that differ in the coordination environment and, therefore, make different contributions to the total energy of the system. The calculated value of the atomization energy for SnO2 is 1661 kJ/mol and corresponds satisfactorily to the experimentally measured specific atomization energy of crystalline SnO2 (1381 kJ/mol). It has been shown that a satisfactory reproduction of the experimental characteristics of crystalline tin dioxide is possible when using clusters containing at least 10 state atoms, for example, (SnO2)10×14H2O.

Theory of polarization-averaged core-level molecular-frame photoelectron angular distributions: III. new formula for p- and s-wave interference analogous to Young's double-slit experiment for core-level photoemission from hetero-diatomic molecules

We present a new variation of Young's double-slit formula for polarization-averaged molecular-frame photoelectron angular distributions (PA-MFPADs) of hetero-diatomic molecules, which may be used to extract the bond length. So far, empirical analysis of the PA-MFPADs has often been carried out employing Young's formula in which each of the two atomic centers emits a s-photoelectron wave. The PA-MFPADs, on the other hand, can consist of an interference between the p-wave from the X-ray absorbing atom emitted along the molecular axis and the s-wave scattered by neighboring atom, within the framework of Multiple Scattering theory. The difference of this p-s wave interference from the commonly used s-s wave interference causes a dramatic change in the interference pattern, especially near the angles perpendicular to the molecular axis. This change involves an additional fringe, urging us to caution when using the conventional Young's formula for retrieving the bond length. We have derived a new formula analogous to Young's formula but for the p-s wave interference. The bond lengths retrieved from the PA-MFPADs via the new formula reproduce the original C-O bond lengths used in the reference ab-initio PA-MFPADs within the relative error of 5 %. In the high energy regime, this new formula for p-s wave interference converges to the ordinary Young’s formula for the s-s wave interference. We expect it to be used to retrieve the bond length for time-resolved PA-MFPADs instead of the conventional Young's formula.

Low-Cycle Fatigue of FRP Strips Glued to a Quasi-Brittle Material

This paper aims at further advancing the knowledge about the cyclic behavior of FRP strips glued to quasi-brittle materials, such as concrete. The results presented herein derive from a numerical model based on concepts of based on fracture mechanics and already presented and validated by the authors in previous works. Particularly, it assumes that fracture processes leading to debonding develop in pure mode II, as is widely accepted in the literature. Starting from this assumption (and having clear both its advantages acnd shortcomings), the results of a parametric analysis are presented with the aim of investigating the role of both the mechanical properties of the interface bond–slip law and a relevant geometric quantity such as the bond length. The obtained results show the influence of the interface bond–slip law and FRP bond length on the resulting cyclic response of the FRP-to-concrete joint, the latter characterized in terms of S-N curves generally adopted in the theory of fatigue. Far from deriving a fully defined correlation among those parameters, the results indicate general trends that can be helpful to drive further investigation, both experimental and numerical in nature.

Applying first principles to study the structural, electronic, and magnetic properties of Pr adsorbed ASiNRs

Applying first-principles calculations, the investigation of the geometrical and electronic properties of Pr adsorption armchair silicene nanoribbons structure has been established. The results show that the bandgap doped Pr has been changed, which is the case for chemical adsorption on the surface of ASiNRs; this material became metallic with the peak of valance band contact fermi level. Moreover, the survey to find the optimal height 1.82 Å of Pr and 2.24 Å bond length Si-Si, and Si-Si-Si bond angle 108005’, energy adsorption is -7.65 eV, buckling is 0.43 Å with structure stability close to the pristine case, has brought good results for actively creating newly applied materials for the spintronic and optoelectronics field in the future.

Theoretical Study of Solvent Effects on the Electronic and Thermodynamic Properties of Tetrathiafulvalene (TTF) Molecule Based on DFT

Tetrathiafulvalene () is an organosulfur compound used in the production of molecular devices such as switches, sensors, nonlinear optical devices and rectifiers. In this work, a theoretical study on the effects of solvent on TTF molecule was investigated and reported based on Density Functional Theory (DFT) as implemented in Gaussian 03 package using B3LYP/6-31++G(d,p) basis set. Different solvents were introduced as a bridge to investigate their effects on the electronic structure. The HUMO, LUMO, energy gap, global chemical index, thermodynamic properties, NLO and DOS analysis of the TTF molecule in order to determine the reactivity and stability of the molecule were obtained. The results obtained showed that the solvents have effects on the electronic and non-linear-optical properties of the molecule. The optimized bond length revealed that the molecule has strong bond in gas phase with smallest bond length of about 1.0834Å than in the rest of the solvents. It was observed that the molecule is more stable in acetonitrile with HOMO-LUMO gap and chemical hardness of 3.6373eV and 1.8187eV respectively. This indicates that the energy gap and chemical hardness of TTF molecule increases with the increase in polarity and dielectric constant of the solvents. The computed results agreed with the results in the literature. The thermodynamics and NLO properties calculation also indicated that TTF molecule has highest value of specific heat capacity (Cv), total dipole moment () and first order hyperpolarizability () in acetonitrile, while acetone has the highest value of entropy and toluene has a slightly higher value of zero point vibrational energy (ZPVE) than the rest of the solvents. The results show that careful selection of the solvents and basis sets can tune the frontier molecular orbital energy gap of the molecule and can be used for molecular device applications.

An Investigation of the Mechanism on Interfacial Charge Transformation of the TiB2/Cu Composites Studied by the First Principles

The charge communications have been widely existed in the metal materials when they are under the processing, the modeling and the failing. We studied the interfacial charge transformation of the TiB2/Cu composites via the first principles method. The layer thickness was predicted by the interfacial charge communications performed on the regions of the TiB2/Cu interfaces. The layer thickness of the Ti-terminated (TT)TiB2/Cu were predicted longer than those of the B-terminated(BT) TiB2/Cu and contrasting with their average vales as 0.75 (nm) and 0.65 (nm), respectively. The Mulliken population was applied to investigate the bond length, bond population and charge transformation of the six TiB2/Cu models. The Ti-Cu bond was only detected in TT-HCP interfaces among the all TT-TiB2/Cu models, which was further confirmed that the metallic bond of the Ti-Cu with the bond length and population as 2.5 Å and 0.22, respectively. Nevertheless, the B-Cu bond were detected in all BT-TiB2/Cu models, and the bond length and population higher than those of B-Cu bond in chemical complexes. The 5 atomic layers were involved in quantitative analyses of the interfacial charge transformation. The results indicate that the charges lost by interfacial Ti atom were inequivalent obtained by Cu and B atoms which nearby the interfacial Ti atoms of the TT-TiB2/Cu. Comparing with the BT-TiB2/Cu models, the charges acquired by the interfacial B atom were most from the Ti and less from the Cu atoms surrounded the interfacial B atoms.