The grand canonical ensemble Monte Carlo method applied to electrolyte solutions

A grand canonical ensemble Monte Carlo method is developed for application to electrolyte solutions.

The method proves to be of comparable accuracy and speed to the conventional NVT Monte Carlo method for electrolytes but has the added advantage of being able to fix the chemical potential. This latter point is vital for the study of surface phenomena. Application of the method to 1:1 and 2:2 primitive model electrolytes is made as is a comparison with the results of approximate statistical mechanical treatments.     

Phase stability of nanocarbon in one dimension: nanotubes versus diamond nanowires

Since their discovery in 1990, the study of sp2 bonded carbon nanotubes has grown into a field of research in it's own right; however the development of the sp3 analog, diamond nanowires, has been slow. A number of theoretical models have been proposed to compare the relative stability of diamond and graphite at the nanoscale; and more recently, to compare nanodiamonds and fullerenes. Presented here is a study of the phase stability of nanocarbon in one-dimension. The structural energies of carbon nanotubes and diamond nanowires have been calculated using density functional theory within the generalized gradient approximation, and used to determine the atomic heat of formation as a function of size.     

Quantum Monte Carlo calculations of the dissociation energy of the water dimer

We report diffusion quantum Monte Carlo (DMC) calculations of the equilibrium dissociation energy D(e) of the water dimer. The dissociation energy measured experimentally, D(0), can be estimated from D(e) by adding a correction for vibrational effects. Using the measured dissociation energy and the modern value of the vibrational energy Mas et al., [J. Chem. Phys. 113, 6687 (2000)] leads to D(e)=5.00+/-0.7 kcal mol(-1), although the result Curtiss et al., [J. Chem. Phys. 71, 2703 (1979)] D(e)=5.44+/-0.7 kcal mol(-1), which uses an earlier estimate of the vibrational energy, has been widely quoted. High-level coupled cluster calculations Klopper et al., [Phys. Chem. Chem. Phys. 2, 2227 (2000)] have yielded D(e)=5.02+/-0.05 kcal mol(-1). In an attempt to shed new light on this old problem, we have performed all-electron DMC calculations on the water monomer and dimer using Slater-Jastrow wave functions with both Hartree-Fock approximation (HF) and B3LYP density functional theory single-particle orbitals. We obtain equilibrium dissociation energies for the dimer of 5.02+/-0.18 kcal mol(-1) (HF orbitals) and 5.21+/-0.18 kcal mol(-1) (B3LYP orbitals), in good agreement with the coupled cluster results.     

A furnace and environmental cell for the in situ investigation of molten salt electrolysis using high‐energy X‐ray diffraction

This paper describes the design, construction and implementation of a relatively large controlled‐atmosphere cell and furnace arrangement. The purpose of this equipment is to facilitate the in situ characterization of materials used in molten salt electrowinning cells, using high‐energy X‐ray scattering techniques such as synchrotron‐based energy‐dispersive X‐ray diffraction. The applicability of this equipment is demonstrated by quantitative measurements of the phase composition of a model inert anode material, which were taken during an in situ study of an operational Fray–Farthing–Chen Cambridge electrowinning cell, featuring molten CaCl₂ as the electrolyte. The feasibility of adapting the cell design to investigate materials in other high‐temperature environments is also discussed.     

Surface structure of cubic diamond nanowires

Presented are results of our ab initio study of the surface reconstruction and relaxation of (1 0 0) surfaces on diamond nanowires. We have used a density function theory within the generalized-gradient approximation using the Vienna ab initio simulation package, to consider dehydrogenated and hydrogenated surfaces. Edges of nanowires offer a new challenge in the determination of surface structure. We have applied the methodology for stepped diamond (1 0 0) surfaces to this problem, and consider it useful in describing diamond nanowire edges to first approximation. We have found that dimer lengths and atomic layer depths of the C(1 0 0)(2 × 1) and C(1 0 0)(2 × 1):H nanowire surfaces differ slightly from those of bulk diamond and nanodiamond surfaces. The aim of this study is provide a better understanding of the effects of nano-scale surfaces on the stability of diamond nanostructures.     

Hydrodynamic interactions and some new periodic structures in three particle sediments

It is well known that the motion of three particles sedimenting in a Stokes fluid is of a simple periodic function of time if the initial configuration is a horizontal, equilateral triangle. We use the method of induced forces to show that if this ititial configuration is made less symmetric then many much more complex structures, which are still periodic in time, may result which involve a sequence of inequivalent configurations. This confirms that the horizontal isosceles triangle configuration is remarkably robust against perturbations.     

Discrimination of prostate cancer cells by reflection mode FTIR photoacoustic spectroscopy

In this communication reflection mode Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) is used to obtain IR spectra of four prostate and prostate cancer cell line types (CaP) allowing their differentiation by principal components analysis.     

On the formation mechanism of the "pancake" decahedron gold nanoparticle

We have studied the thermodynamic and kinetic growth mechanisms behind the formation of the "pancake" decahedron (D(h)) gold nanoparticle using computer simulation. Free energy calculations showed that the full pancake morphology is thermodynamically unstable across all the nanoparticle size ranges studied. However, from observations of growth simulations we discovered that a kinetic transport mechanism plays a significant contributing role in the formation process through a transfer of adatoms from the top and bottom (111) D(h) faces to the side (100) faces. More specifically we observed how diffusing adatoms on the (111) face are at times "pulled" off this face and into the (111)-(100) edge of the D(h), forcing a row of (100) side atoms into a (1x5) hexagonal reconstruction. Subsequently, this row of atoms was observed to buckle and then deconstruct forcing adatoms out onto the (100) side face completing the transfer. This transport mechanism is shown to be the main kinetic driving force behind the growth of the thermodynamically unstable pancake D(h) nanoparticle. The observed mechanism has implications for the nonequilibrium morphologies of nanoparticles involving a (100)-(111) surface boundary, especially for systems with surface reconstructions which increase the density of the surface.