Emergence of a Low-Energy Peak in the Smoothed Absolute Value Circular Dichroism Spectra of Small Helical Gold Nanorods.

We calculate, using time-dependent density functional theory, absorption and circular dichroism (CD) spectra for a series of small helical gold nanorod structures with a width of 0.6 nm and length increasing from 0.7 nm for Au to 1.

Engineering magic number Au and Au cage structures using electron withdrawing atoms.

Gold cages are a subset of gold nanoparticles and these structures are of major interest due to their favourable physiochemical properties. In order for these structures to be useful in applications, they must be chemically stable. The objective of this research is to transform non-magic number cage structures into magic number cage structures by the addition of electron-withdrawing groups on the cages.

Triskelion Structured Colloidal Quantum Dots.

We show, using density functional theory and ab initio molecular dynamics, that certain small colloidal quantum dots with a mixed nanocrystal core capped with achiral surface ligands spontaneously form a triskelion (from the Greek, three-legged) structure with (approximate) symmetry that can be dynamically stable at room temperature when additionally capped with small amine ligands. Furthermore, the nanocrystal core also forms a triskelion structure. The focus of our study is a colloidal quantum dot with a CdSeTe core (and a charge of +12) capped with negatively charged surface ligands to achieve charge neutrality-in the simplest instance, 12 Cl-to form the colloidal quantum dot CdSeTeCl.

Bonding and metastability for Group 12 dications.

Electronic structure and bonding properties of the Group 12 dications M (M = Zn, Cd, Hg) are investigated and electron density-derived quantities are used to characterize the metastability of these species. Of particular interest are the complementary descriptions afforded by the Laplacian of the electron density ∇ ρ(r) and the one-electron Bohm quantum potential (Q =  ) along the bond path. Further, properties derived from the pair density including the localization-delocalization matrices (LDMs) and the interacting quantum atoms (IQA) energies are analyzed within the framework of the quantum theory of atoms in molecules (QTAIM).

Stabilization of Columnar Liquid Crystal Phases via Arene-Perfluoroarene Interactions.

We report the synthesis of novel polycatenar dibenzopentacenequinones and that are designed to form columnar liquid crystalline phases. The mesomorphic properties of these compounds were investigated by polarized optical microscopy, differential scanning calorimetry, and powder X-ray diffraction. While compound exhibits two distinct columnar mesophases between 148 and 177 °C, fluorinated exhibits a columnar mesophase from 121 to 336 °C.

Iron doped gold cluster nanomagnets: determination of barriers for demagnetization.

Magnetic properties of small- and nano-sized iron doped gold clusters are calculated at the level of second order multireference perturbation theory. We first assess the methodology for small AuFe and AuFe clusters, which are representative of even and odd electron count systems. We find that larger active spaces are needed for the odd electron count system, AuFe, which exhibits isotropic magnetization behaviour.

(Meta-)stability and Core-Shell Dynamics of Gold Nanoclusters at Finite Temperature.

Gold nanoclusters have been the focus of numerous computational studies, but an atomistic understanding of their structural and dynamical properties at finite temperature is far from satisfactory. To address this deficiency, we investigate gold nanoclusters via ab initio molecular dynamics, in a range of sizes where a core-shell morphology is observed. We analyze their structure and dynamics using state-of-the-art techniques, including unsupervised machine-learning nonlinear dimensionality reduction (sketch-map) for describing the similarities and differences among the range of sampled configurations.

A series of intrinsically chiral gold nanocage structures.

We present a series of intrinsically chiral gold nanocage structures, Au, which are stable for n ≥ 2. These structures consist of an Au tube which is capped with Au units at each end. Removing the Au caps, we obtain a series of intrinsically chiral gold nanotube structures, Au, which are stable for n ≥ 4.

Dispersion Effects on the Thermodynamics and Transition States of Dimethylarsinic Acid Adsorption on Hydrated Iron (Oxyhydr)oxide Clusters from Density Functional Theory Calculations.

Reaction pathway information and transition states are crucial for understanding adsorption mechanisms of pollutants, such as dimethylarsinic acid (DMA), at the liquid-solid interface. We report a detailed computational analysis of the complexes of DMA on iron (oxyhydr)oxides, including activation energies, transition states, Gibbs free energies of adsorption, Mulliken charges, charge redistribution upon adsorption, and stretching frequencies of As-O bonds for comparison with experimental spectroscopic data. Calculations were performed using density functional theory (DFT) at the B3LYP/6-311+G(d,p) level using both implicit and explicit hydration.

Helical gold nanorods as chiral recognition nanostructures: a relativistic density functional theory study.

We establish helical gold nanorods as the first examples of chiral recognition nanostructures by examining the simple chiral molecule CClHDT adsorbed on the helical Au40 nanorod. We calculate the vibrational circular dichroism (VCD) spectra of the R and S enantiomers of CClHDT adsorbed on the R (or S) enantiomer of Au40 using relativistic density functional theory. The highest adsorption energy is found when the Cl atom of CClHDT binds to a low-coordinated Au atom at the edge of Au40.

Density functional theory calculations on the complexation of p-arsanilic acid with hydrated iron oxide clusters: structures, reaction energies, and transition states.

Aromatic organoarsenicals, such as p-arsanilic acid (pAsA), are still used today as feed additives in the poultry and swine industries in developing countries. Through the application of contaminated litter as a fertilizer, these compounds enter the environment and interact with reactive soil components such as iron and aluminum oxides. Little is known about these surface interactions at the molecular level.

Formation of chlorinated species through reaction of SO₂ with NaClO₂ powder and their role in the oxidation of NO and Hg⁰.

This study examines gaseous chlorinated species generated from the reaction of sulfur dioxide (SO₂) with sodium chlorite powder (NaClO₂(s)) to obtain insight into the propensity of this process to enhance NO and Hg⁰ oxidation. A packed bed reactor containing NaClO₂(s) was used and the reaction temperature was set to 130 °C. Initially, we determined that the presence of SO₂ enhances the oxidation of NO and Hg⁰ by reaction with NaClO₂(s).

Thermodynamics of dimethylarsinic acid and arsenate interactions with hydrated iron-(oxyhydr)oxide clusters: DFT calculations.

Dimethylarsinic Acid (DMA) belongs to an important class of organoarsenical compounds commonly detected in arsenic speciation studies of environmental samples and pyrolysis products of fossil fuels. Transformation of DMA under certain conditions leads to the formation of other forms of arsenic, which could be more toxic than DMA to biota, and more efficient in deactivating catalysts used in petrochemical refining. Published surface sensitive X-ray and infrared spectroscopic work suggested that DMA simultaneously forms inner- and outer-sphere complexes with iron-(oxyhydr)oxides.

Relativistic-consistent electron densities of the coinage metal clusters M2, M4, M4(2-), and M4Na2 (M = Cu, Ag, Au): a QTAIM study.

We employ second-order Møller-Plesset perturbation theory level in combination with recently developed pseudopotential-based correlation consistent basis sets to obtain accurate relativistic-consistent electron densities for small coinage metal clusters. Using calculated electron densities, we employ Bader's quantum theory of atoms in molecules (QTAIM) to gain insights into the nature of metal-metal bonding in the clusters M(2), M(4), M(4)(2-), and M(4)Na(2) (M = Cu, Ag, Au). For the simplest case of the metal dimer, M(2), we correlate the strength of the metal-metal bond with the value of the electron density at the bond critical point, the total energy density at the bond critical point, the sharing (delocalization) index, and the values of the two principle negative curvatures.

Alignment of colloidal graphene quantum dots on polar surfaces.

Controlling the orientation of nanostructures with anisotropic shapes is essential for taking advantage of their anisotropic electrical, optical, and transport properties in electro-optical devices. For large-area alignment of nanocrystals, so far orientations are mostly induced and controlled by external physical parameters, such as applied fields or changes in concentration. Herein we report on assemblies of colloidal graphene quantum dots, a new type of disk-shaped nanostructures, on polar surfaces and the control of their orientations.

Insights into the surface complexation of dimethylarsinic acid on iron (oxyhydr)oxides from ATR-FTIR studies and quantum chemical calculations.

The surface chemistry of methylated arsenicals with ubiquitous geosorbents and industrial catalysts is poorly understood. These arsenic compounds pose both a health and an environmental risk in addition to being a challenge to the energy industry. We report herein a detailed spectroscopic analysis of the surface structure of dimethylarsinic acid (DMA) adsorbed on hematite and goethite using attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR).

Experimental and theoretical study on activation of the C-H bond in pyridine by [M(m)]- (M = Cu, Ag, Au, m = 1-3).

Activation of the C-H bond of pyridine by [M(m)](-) (M = Cu, Ag, Au, m = 1-3) is investigated by experiment and theory. Complexes of coinage metal clusters and the pyridyl group, [M(m)-C(5)H(4)N](-), are produced from reactions between metal clusters formed by laser ablation of coinage metal samples and pyridine molecules seeded in argon carrier gas. We examine the structure and formation mechanism of these pyridyl-coinage metal complexes.

Interacting electrons, spin statistics, and information theory.

We consider a nearly (or quasi) uniform gas of interacting electrons for which spin statistics play a crucial role. A previously developed procedure, based on the extension of the Levy-Lieb constrained search principle and Monte Carlo sampling of electron configurations in space, allows us to approximate the form of the kinetic-energy functional. For a spinless electron gas, this procedure led to a correlation term, which had the form of the Shannon entropy, but the resulting kinetic-energy functional does not satisfy the Lieb-Thirring inequality, which is rigorous and one of the most general relations regarding the kinetic energy.

Investigations of strong hydrogen bonding in (ROH)n...FHF- (n = 1, 2 and R = H, CH3, C2H5) clusters via high-pressure mass spectrometry and quantum calculations.

An examination of strong hydrogen bonds found in (ROH)(n)...