Convergence of the partial wave expansion of the He ground state

The configuration interaction (CI) method, using a very large Laguerre orbital basis, is applied to the calculation of the He ground state. The largest calculations included a minimum of 35 radial orbitals for each ? ranging from 0 to 12, resulting in basis sets in excess of 400 orbitals. The convergence of the energy and electron–electron δ‐function with respect to J (the maximum angular momenta of the orbitals included in the CI expansion) were investigated in detail. Extrapolations to the limit of infinite angular momentum using expansions of the type ΔX_J = A_X[J + 1/2]^?p + B_X[J + 1/2]^?p?1 + …, gave an energy accurate to 10^?7 Hartree and a value of 〈δ〉 accurate to about 0.5%. Improved estimates of 〈E〉 and 〈δ〉, accurate to 10^?8 Hartree and 0.01%, respectively, were obtained when extrapolations to an infinite radial basis were done prior to the determination of the J → ∞ limit. Round‐off errors were the main impediment to achieving even higher precision, since determination of the radial and angular limits required the manipulation of very small energy and 〈δ〉 differences. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Effect of cation distribution on self-diffusion of molecular hydrogen in Na3Al3Si3O12 sodalite: a molecular dynamics study

The diffusion of hydrogen in sodium aluminum sodalite (NaAlSi-SOD) is modeled using classical molecular dynamics, allowing for full flexibility of the host framework, in the temperature range 800-1200 K. From these simulations, the self-diffusion coefficient is determined as a function of temperature and the hydrogen uptake at low equilibrium hydrogen concentration is estimated at 573 K. The influence of the cation distribution over the framework on the hydrogen self-diffusion is investigated by comparing results employing a low energy fully ordered cation distribution with those obtained using a less ordered distribution. The cation distribution is found to have a surprisingly large influence on the diffusion, which appears to be due to the difference in framework flexibility for different cation distributions, the occurrence of correlated hopping in case of the ordered distribution, and the different nature of the diffusion processes in both systems. Compared to our previously reported calculations on all silica sodalite (all-Si-SOD), the hydrogen diffusion coefficient of sodium aluminum sodalite is higher in the case of the ordered distribution and lower in case of the disordered distribution. The hydrogen uptake rates of all-Si-SOD and NaSiAl-SOD are comparable at high temperatures (approximately 1000 K) and lower for all-Si-SOD at lower temperatures (approximately 400 K).     

Influence of substrate dopant type on the optical properties of GaInAs/InP multiquantum well structures grown by low pressure MOVPE

A correlation between substrate dopant type and the absorption spectra of MQW structures has been identified. Optical absorption spectra from MQW structures grown on S-doped InP can show poorly resolved excitonic features with respect to those obtained from structures grown on both Sn- and Fe-doped substrates. It is proposed that this degradation is due to enhanced interfacial diffusion on the Group V sublattice for structures grown on substrates incorporating low defect densities.     

Convergence of an s‐Wave calculation of the He ground state

The configuration interaction (CI) method using a large Laguerre basis restricted to ? = 0 orbitals is applied to the calculation of the He ground state. The maximum number of orbitals included was 60. The numerical evidence suggests that the energy converges as ΔE^N ≈ A/N^7/2 + B/N^8/2 + …, where N is the number of Laguerre basis functions. The electron–electron δ‐function expectation converges as Δδ^N ≈ A/N^5/2 + B/N^6/2 + …, and the variational limit for the ? = 0 basis is estimated as 0.1557637174(2) a. It was seen that extrapolation of the energy to the variational limit is dependent on the basis dimension at which the exponent in the Laguerre basis was optimized. In effect, it may be best to choose a nonoptimal exponent if one wishes to extrapolate to the variational limit. An investigation of the natural orbital asymptotics revealed the energy converged as ΔE^N ≈ A/N⁶ + B/N⁷ + …, while the electron–electron δ‐function expectation converged as Δδ^N ≈ A/N⁴ + B/N⁵ + …. The asymptotics of expectation values other than the energy showed fluctuations that depended on whether N was even or odd. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Negative differential resistance (NDR) in similar molecules with distinct redox behaviour

The transport characterization of self-assembled monolayers (SAMs) based on the closed and open-shell forms of a fully conjugated polychlorotrimethylphenyl (PTM) derivative hybridized with the gold substrate reveals that both systems exhibit negative differential resistance (NDR) in their I-V curves which was attributed to similar resonant tunnelling with unoccupied molecular orbitals. This work demonstrates that distinct transport mechanisms can dominate depending on the bias-voltage applied and shows that NDR processes are not influenced here by the redox character of the molecules.     

ChemInform Abstract: Density Functional Studies of Model Cerium Oxide Nanoparticles.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.