A theoretical study of the structural and electronic properties of some titanocenes using DFT,TD-DFT,and QTAIM

Structural Chemistry - Titanocenes are gradually proven to possess good anticancer activity. In this paper, we present a theoretical study of some properties of six promising anticancer titanocenes...     

Numerical simulation of axisymmetric turbulent flow in combustors and diffusers

Numerical studies of turbulent flow in an axisymmetric 45° expansion combustor and bifurcated diffuser are presented. The Navier-Stokes equations incorporating a k–? model were solved in a non-orthogonal curvillinear co-ordinate system. A zonal grid method, wherein the flow field was divided into several subsections, was developed. This approach permitted different computational schemes to be used in the various zones. In addition, grid generation was made a more simple task. However, treatment of the zonal boundaries required special handling. Boundary overlap and interpolating techniques were used and an adjustment of the flow variables was required to assure conservation of mass flux. Three finite differencing methods—hybrid, quadratic upwind and skew upwind—were used to represent the convection terms. Results were compared with existing experimental data. In general, good agreement between predicted and measured values was obtained.     

DFT-based study of the impact of transition metal coordination on the charge transport and nonlinear optical (NLO) properties of 2-{[5-(4-nitrophenyl)-1,3,4-thiadiazol-2-ylimino]methyl}phenol

Theoretical investigations of the impact of transition metal chelation on the electron/hole-transport and nonlinear optical (NLO) properties of 2-{[5-(4-nitrophenyl)-1,3,4-thiadiazol-2-ylimino]methyl}phenol (L) are reported herein. Calculations were carried out via density functional theory (DFT)-based methods, employing exchange–correlation functionals and basis sets of different qualities. Results have shown that free L is a moderate electron/hole-transporter, but that its Pd(II) and Pt(II) complexes are excellent hole- and electron-transport materials respectively, owing to their very small reorganisation energies and relatively large electronic coupling matrix elements or transfer integrals. These results indicate that the complexes are potentially suitable charge transport materials for the construction of organic light emitting diodes (OLEDs). Nevertheless, the results also revealed a higher NLO activity for L than its metal complexes. Interestingly, the first and second hyperpolarizabilities, along with some computed NLO properties of both L and its complexes are found to be remarkably higher than those of the prototypical push–pull molecule, para-nitroaniline. Accordingly, these compounds are potential candidates for the fabrication of optoelectronic and photonic devices for second- and third-order NLO applications. Summarily, metal chelation is found to enhance the charge transport properties in some cases, and to slightly diminish NLO response of L in all cases investigated.     

Lagrangian based heuristics for the multicommodity network flow problem with fixed costs on paths

We study the multicommodity network flow problem with fixed costs on paths, with specific application to the empty freight car distribution process of a rail operator. The classification costs for sending a group of cars do not depend on the number of cars in the group, as long as the group is kept together as one unit. Arcs correspond to trains, so we have capacity restrictions on arcs but fixed costs on the paths corresponding to routes for groups of cars. As solution method, we propose a Lagrangian based heuristic using dual subgradient search and primal heuristics based on path information of the Lagrangian subproblem solutions. The method illustrates several ways of exploiting the specific structures of the problem. Computational tests indicate that the method is able to generate fairly good primal feasible solutions and lower bounds on the optimal objective function value.