Volume 127, Issue 14, 14 October 2007
Index of content:
Determination of structural transitions of atomic clusters from local and global bond orientational order parameters127(2007); http://dx.doi.org/10.1063/1.2794032View Description Hide Description
Designing an effective order parameter for the identification of geometries in atomic clusters is an important step toward understanding the structuraltransitions occurring in these systems. We propose a method that simultaneously utilizes the local and global bond orientational order parameters for structuraltransitions. When applied to Lennard–Jones clusters at finite temperature over the size range , this method identified all the major geometries: icosahedra with Mackay overlayers, icosahedra with anti-Mackay overlayers, decahedra, octahedra, and tetrahedra. From the distributions of these geometries as a function of temperatures on clusters containing 38, 75, and 98 atoms, we are able to interpret all transition types without ambiguity.
The origin of deficiency of the supermolecule second-order Møller-Plesset approach for evaluating interaction energies127(2007); http://dx.doi.org/10.1063/1.2795693View Description Hide Description
Calculations for the complex of thymine and adenine are used to show that the supermolecule second-order Møller-Plesset perturbation theory (MP2) approach for evaluating interaction energies fails in certain cases because of the behavior of one of its components: the uncoupled Hartree-Fock dispersion energy. A simple approach for correcting the MP2 supermolecule interaction energies is proposed. It focuses on correcting a relatively small difference between the MP2 and coupled cluster interaction energies, which is a very appealing feature of the new approach considering a benchmark role played by coupled cluster results.
127(2007); http://dx.doi.org/10.1063/1.2795694View Description Hide Description
We present, within the framework of intracule functionaltheory (IFT), a class of kernels whose correlationintegrals can be found in closed form. This approach affords three major advantages over other kernels that we have considered previously; ease of implementation, computational efficiency, and numerical stability. We show that even the simplest member of the class yields reasonable estimates of the correlation energies of 18 atomic and 56 molecular systems and we conclude that this kernel class will prove useful in the development of future IFT models.
127(2007); http://dx.doi.org/10.1063/1.2796151View Description Hide Description
In the context of investigating organic molecules for molecular electronics, doping molecular wires with transition metal atoms provides additional means of controlling their transport behavior. The incorporation of transition metal atoms may generate spin dependence because the conduction channels of only one spin component align with the chemical potential of the leads, resulting in a spin polarized electric current. The possibility to create such a spin polarized current is investigated here with the organometallic moiety cobaltocene. According to our calculations, cobaltocene contacted with gold electrodes acts as a robust spin filter: Applying a voltage less than causes the current of one spin component crossing the molecular bridge to be two orders of magnitude larger than the other. We address the key issue of sensitivity to molecule-lead geometry by showing that a weak barrier generated by groups between the cobaltocene and the leads is crucial in reducing the sensitivity to the contact geometry while only reducing the current modestly. These results suggest cobaltocene as a robust basic building block for molecular spintronics.
127(2007); http://dx.doi.org/10.1063/1.2798103View Description Hide Description
This work elucidates photoinduced two-dimensional (2D) gratings in dye-doped cholesteric liquid crystalfilms. The helical pitch is increased by green-beam-induced trans-cisisomerization and a concomitant thermal effect. Two-dimensional gratings appear when the green beam is turned off. Grating formation results from elastic instability caused by restored strain arising from helical pitch reduction. Grating lifetime increases as green beam intensity increases and declines under irradiation with a strong red beam. Variation in grating spacing with green intensity with various pitches is also examined.