Sources of error in electronic structure calculations on small chemical systems

The sources of error in electronic structure calculations arising from the truncation of the one-particle and n-particle expansions are examined with very large correlation consistent basis sets, in some cases up through valence 10-zeta quality, and coupled cluster methods, up through connected quadruple excitations. A limited number of full configuration interaction corrections are also considered. For cases where full configuration interaction calculations were unavailable or prohibitively expensive, a continued fraction approximation was used. In addition, errors arising from corevalence and relativistic corrections are also probed for a number of small chemical systems. The accuracies of several formulas for estimating total energies and atomization energies in the complete basis set limit are compared in light of the present large basis set findings. In agreement with previous work, the CCSD(T) method is found to provide results that are closer to the CCSDTQ and full configuration-interaction results than the less approximate CCSDT method.     

Radiation forces exerted on arbitrarily located sphere by acoustic tweezer

In a previous paper acoustic radiation force on a lipid sphere in a 100-MHz focused Gaussian field was calculated to demonstrate the acoustic tweezer effect near the focus. The theoretical formulation was based on the situation where the sphere is centered along the beam axis. Given intensity distribution independent of the x axis, it was then approximated by a cylindrical model for the sake of simplicity. Only the axial forces were considered because no lateral forces exist due to an object's symmetry. However, it was difficult to employ the same technique to the more general case when it is off the beam axis. To overcome the limitation, in this paper the previous model is modified to compute two additional lateral forces by carrying out the projection over arbitrary incident planes to restrict the integration limits. For different sizes of the sphere, the magnitudes of the net forces in three orthogonal directions are computed. The results show that the acoustic tweezer can be realized more easily in the lateral directions than in the axial directions. Differing from the axisymmetric case, the spheres of small sizes tend to be more strongly attracted than the larger ones in the lateral directions.     

An iridium(III) complex that exhibits dual mechanism nonlinear absorption

The photophysical properties of the complex (L)Ir(ppy)(2)(+), where ppy = 2-phenylpyridine and L = 4,4'-(2,2'-bipyridine-5,5'-diylbis(ethyne-2,1-diyl))bis(N,N-dihexylaniline), have been investigated under one- and two-photon excitation conditions. In THF solution, the complex exhibits broad ground-state absorption with lambda(max) approximately 500 nm and weak photoluminescence with lambda(max) approximately 730 nm. Excitation of (L)Ir(ppy)(2)(+) at 355 nm produces a long-lived excited state (tau approximately 1 mus) that features a strong excited-state absorption in the near-infrared (lambda(max) approximately 875 nm, Deltaepsilon approximately 6.1 x 10(4) M(-1) cm(-1)). Photoluminescence and transient absorption studies of (L)Ir(ppy)(2)(+) carried out using 5 ns, 1064 nm pulsed excitation demonstrate that the same long-lived and strongly absorbing excited state can be efficiently produced by two-photon absorption. Solutions of the complex in THF display nonlinear absorption of 5 ns, 1064 nm pulses in a process that is believed to involve a combination of two-photon absorption and reverse saturable absorption.     

Die Herstellung von Glasfritten aus Pyrexglas

Ohne Zusammenfassung     

Asymptotic pointwise contractions

A simple and elementary (without using the ultrapower technique) proof for the existence of a fixed point of an asymptotic pointwise contraction is provided. The existence of fixed points for asymptotic pointwise nonexpansive mappings in a uniformly convex Banach space is also investigated.     

The crystal structure of synthetic simmonsite, Na2LiAlF6

The structure of the synthetic fluoroperovskite, Na₂LiAlF₆ (simmonsite), has been determined by powder X-ray diffraction using the Rietveld method of structure refinement. The compound adopts space group P2₁/n [#14; a=5.2842(1); b=5.3698(1); c=7.5063(2)Å; β=89.98(1)°; Z=4), and is a member of the cryolite (Na₂NaAlF₆) structural group characterized by ordering of the B-site cations (Li, Al) and tilting of the BF₆ octahedra according to the tilt scheme a⁻b⁻c⁺. Rotations of the B-site polyhedra are less (Φ_Li=14.9°; Φ_Al=17.0°) than those found in cryolite (Φ_Na=18.6; Φ_Al=23.5°) because of the larger difference in the ionic radii of the B-site cations in cryolite as compared to those in simmonsite. Na at the A-site is displaced from the special position resulting in 10- and 8-fold coordination in simmonsite and cryolite, respectively. By analogy with the synthetic compound, naturally occurring simmonsite is considered to adopt space group P2₁/n (#14) and not the P2₁(#4) or P2₁/m(#11) space groups.     

Speciation and unusual reactivity in PuO2+x

Pu L(3) XAFS measurements show that the excess oxygen in single phase PuO(2+)(x)() occurs as oxo groups with Pu-O distances of 1.83-1.91 A. This distance and the energy of the edge (via comparison with a large number of related compounds) are more consistent with a Pu(IV/V) than a Pu(IV/VI) mixture. Analogous to Pu(IV) colloids, although the Pu-Pu pair distribution remains single site even when it shows substantial disorder, the Pu-O distribution can display a number of additional shells at specific distances up to 3.4 A even in high fired materials when no oxo groups are present, implying intrinsic H(+)/OH(-)(/H(2)O). The number of oxo atoms increases when samples are equilibrated with humid air at ambient temperature, indicating that the Pu reactivity in this solid system differs notably from that of isolated complexes and demonstrating the importance of nanoscale cooperative phenomena and total free energy in determining its chemical properties.     

Amplified quenching in metal-organic conjugated polymers

The luminescence from conjugated polyelectrolytes that contain pendant metal complex units is quenched very efficiently by oppositely charged electron acceptors.