I2 as an efficient catalyst in ionic Diels-Alder reactions of α,β-unsaturated acetals

A variety of protected and unprotected α,β-unsaturated aldehydes react with 1,3-dienes in the presence of I₂ to give the corresponding cycloadducts.     

Nonlocal Wigner-like correlation energy density functional: parametrization and tests on two-electron systems

Reparametrization of Wigner's correlation energy density functional yields a very close fit to the correlation energies of the helium isoelectronic sequence. However, a quite different reparametrization is required to obtain an equally close fit to the isoelectronic sequence of Hooke's atom. In an attempt to avoid having to reparametrize the functional for different choices of the one-body potential, we propose a parametrization that depends on global characteristics of the ground-state electron density as quantified by scale-invariant combinations of expectation values of local one-body operators. This should be viewed as an alternative to the density-gradient paradigm, allowing one to introduce the nonlocal dependence of the density functional on the density in a possibly more effective way. Encouraging results are obtained for two-electron systems with one-body potentials of the form r(zeta) with zeta=-12,+12,1, which span the range between the Coulomb potential (zeta=-1) and the Hooke potential (zeta=2).     

Gross alpha determination in salt rich water samples using an extraction chromatographic resin and LSC

The application of an extraction chromatographic resin to the determination of the gross alpha activity of drinking water samples with volumes greater than 100 ml and of salt rich aqueous samples, like mineral, waste or sea waters was tested. Alpha-emitters are extracted from the water sample onto the resin, the gross alpha activity is then determined by direct measurement of the dried resin using α/β discrimination LSC. The resin shows strong affinity for actinides, as well as for radium, out of pH 2 solutions. The extraction is robust against Ca, sulphate and other potential interferents. The method was tested by analyzing reference materials, intercomparison samples and spiked real samples. Results of good precision and accuracy were obtained in counting times notably shorter than routinely used for gas proportional counting.     

More on basis set quality tests

The quality measure δ of Sordo and Pueyo is computed for 94 orbital basis sets for the atomic helium Hartree-Fock problem and compared with various information theoretic quality measures reported previously by us for this data base. δ is in error often enough that it is unlikely to be a useful general purpose measure.     

The quality of s-orbitals determined by least-squares fitting and constrained variational methods

Calculations of a wide range of position and momentum space properties of 23 orbital basis sets for atomic helium are performed to supplement our previous work. The combined results on 94 orbital basis sets are used to demonstrate that, as in the case of d-orbitals, the least squares error is not as discriminating as other information theoretic measures of overall quality for s-orbitals. Detailed comparisons suggest that constrained variation can improve the overall quality of the resulting orbital provided that the constraints are selected carefully to complement the bias inherent in the energy expectation value and the functional form of the basis functions.     

When does the non-variational nature of second-order Møller-Plesset energies manifest itself? All-electron correlation energies for open-shell atoms from K to Br

All-electron correlation energies E(c) are not very well known for open-shell atoms with more than 18 electrons. The complete basis-set (CBS) limits of second-order M?ller-Plesset (MP2) perturbation theory energies are obtained for open-shell atoms by computations in large basis sets combined with a knowledge of the MP2/CBS limit for the next larger closed-shell atom with the same valence shell structure. Then higher-order correlation corrections are found by coupled-cluster calculations using basis sets that are not quite as large. The method is validated for the open-shell atoms from Al to Cl for which E(c) is reasonably well established. Then, the method is used to obtain non-relativistic E(c) values, probably accurate to 3%, for the open-shell atoms of the fourth period: K, Sc-Cu, and Ga-Br. These energies are compared with the predictions of 19 density functionals and may be useful for the parameterization of new ones. The results show that MP2 overestimates |E(c)| for atoms heavier than Fe.     

Polarisation and polishing studies on copper in a Hull cell

In continuation of our previous work,^1–2 the effects of polishing time, sp. gr. of the electrolyte, addition of EDTA, electrolyte level, etc., on the position, size and shape of the variously polished bands obtained in a Hull cell have now been studied. I–V measurement when carried out showed that total cell voltage increases regularly with total cell current, thereby affording no explanation for the variously polished bands. However, with a specially designed probe electrode,³ it has been possible to study the current distribution as existing during polarisation at different points of the anode surface and thus offer some explanation for the appearance of variously polished bands which could not be interpreted earlier in terms of electrode potentials.     

Numerical Hartree–Fock results for atoms Cs through Lr

Accurate nonrelativistic numerical Hartree–Fock results are reported for the heavy atoms Cs (Z = 55) through Lr (Z = 103) in their ground states. © 1995 John Wiley & Sons, Inc.     

Model studies of the Tamm-like and field-sustained surface states of germanium

The effects of varying the intensity of an applied positive electric field on the Tamm-like and field-sustained surface states of a semi-infinite 6-well model of germanium are studied. The effects of a neon image gas atom on such states are also examined. It is found that there are ranges of the field intensity for which field-sustained surface states do not exist. The localization properties of electrons in the various surface states are discussed with the help of relative probability density functions. As is well-known, electrons in Tamm-like states in the first forbidden energy gap tend to be strongly localized near the surface and inside the crystal. However those in Tamm-like states in higher gaps do not exhibit any pronounced localization. Electrons in field-sustained surface states tend to be strongly localized outside the crystal.