Assessing impacts of simulated oil spills on the Northeast Arctic cod fishery.

We simulate oil spills of 1500 and 4500m/day lasting 14, 45, and 90days in the spawning grounds of the commercial fish species, Northeast Arctic cod. Modeling the life history of individual fish eggs and larvae, we predict deviations from the historical pattern of recruitment to the adult population due to toxic oil exposures. Reductions in survival for pelagic stages of cod were 0-10%, up to a maximum of 43%.

Gauge-Origin Independent Calculations of the Anisotropy of the Magnetically Induced Current Densities.

Gauge-origin independent current density susceptibility tensors have been computed using the gauge-including magnetically induced current (GIMIC) method. The anisotropy of the magnetically induced current density (ACID) functions constructed from the current density susceptibility tensors are therefore gauge-origin independent. The ability of the gauge-origin independent ACID function to provide quantitative information about the current flow along chemical bonds has been assessed by integrating the cross-section area of the ACID function in the middle of chemical bonds.

The contribution of intra- and interspecific tolerance variability to biodiversity changes along toxicity gradients.

The worldwide distribution of toxicants is an important yet understudied driver of biodiversity, and the mechanisms relating toxicity to diversity have not been adequately explored. Here, we present a community model integrating demography, dispersal and toxicant-induced effects on reproduction driven by intraspecific and interspecific variability in toxicity tolerance. We compare model predictions to 458 species abundance distributions (SADs) observed along concentration gradients of toxicants to show that the best predictions occur when intraspecific variability is five and ten times higher than interspecific variability.

Calculation of spin-current densities using gauge-including atomic orbitals.

The gauge-including magnetically induced current method for calculating the components of the current-density tensor using gauge-including atomic orbitals has been extended to treating open-shell molecules. The applicability of the method is demonstrated by calculations of first-order induced current densities on cyclobutadiene, Al(3), and B(3) at correlated ab initio levels of theory. For comparison, current-density calculations were also performed on the lowest closed-shell singlet state of cyclobutadiene as well on the closed-shell Al(3)(-) and B(3)(-) anions.

Magnetically induced current densities in aromatic, antiaromatic, homoaromatic, and nonaromatic hydrocarbons.

The magnetically induced current densities for ring-shaped hydrocarbons are studied at the density functional theory (DFT) and second-order Møller-Plesset (MP2) levels using gauge-including atomic orbitals. The current densities are calculated using the gauge-including magnetically induced current approach. The calculations show that all studied hydrocarbon rings sustain strong diatropic and paratropic ring currents when exposed to an external magnetic field, regardless whether they are unsaturated or not.

NMR shielding constants in BF(3) and magnetic dipole moments of (11)B and (10)B nuclei.

Gas-phase NMR spectra of (11)B, (10)B, and (19)F in BF(3) are reported, and high-level ab initio calculations of the corresponding NMR shielding constants are described. Extrapolation of the measured resonance frequencies to the zero-density limit ensures that the results correspond to the ab initio values for an isolated molecule. Simultaneous measurements of (3)He resonance frequencies and application of the calculated shielding constants allow us to determine improved values of the nuclear magnetic dipole moments of (11)B and (10)B.

Calculation of magnetically induced currents in hydrocarbon nanorings.

Magnetically induced current densities, nuclear magnetic shieldings, and electric polarizabilities of planar ring-shaped hydrocarbons have been studied at the density-functional theory level using the Becke-Perdew (BP86) functional. The current densities were calculated using the Gauge-Including Magnetically Induced Current (GIMIC) method employing gauge-including atomic orbitals. The GIMIC calculations yield rules to estimate the global and local ring-current strengths as well as the current pathways for the hydrocarbon nanorings.

Polycyclic antiaromatic hydrocarbons.

Magnetically induced current densities have been calculated for a series of hydrocarbons consisting of hexadehydro[12]annulene rings alternatingly fused with benzenes. The calculations show that all molecular rings of the studied molecules sustain paramagnetic ring currents. The new class of molecules is therefore coined polycyclic antiaromatic hydrocarbons (PAAH).

Parallel implementation of a direct method for calculating electrostatic potentials.

The authors present a method for calculating the electrostatic potential directly in a straightforward manner. While traditional methods for calculating the electrostatic potential usually involve solving the Poisson equation iteratively, the authors obtain the electrostatic interaction potential by performing direct numerical integration of the Coulomb-law expression using finite-element functions defined on a grid. The singularity of the Coulomb operator is circumvented by an integral transformation and the resulting auxiliary integral is obtained using Gaussian quadrature.

On the Aromaticity of the Planar Hydrogen-Bonded (HF)3 Trimer.

The nuclear magnetic shieldings and magnetically induced ring currents have been calculated for the planar ring-shaped hydrogen fluoride trimer (HF)3 at correlated ab initio and density functional theory levels. Calculations of the magnetically induced current densities using the gauge-including magnetically induced current (GIMIC) method show that, contrary to a recent suggestion, (HF)3 has, at the MP2/TZVPP level, a very small ring-current susceptibility of 0.37 nA/T.

Experimental and computational studies of alkali-metal coinage-metal clusters.

Coinage and alkali metal mixed clusters, M4Na- (M = Cu, Au) have been investigated experimentally using photoelectron spectroscopy and computationally at correlated ab initio levels. The related Cu4Li-, Ag4Li-, Ag4Na-, and Au4Li- clusters as well as the neutral Cu4Li2 and Cu4Na2 clusters have also been studied computationally. The calculations show that the two lowest isomers of the negatively charged clusters include a pyramidal C4v structure and a planar C2v species.

Magnetically induced current densities in Al4 (2-) and Al4 (4-) species studied at the coupled-cluster level.

Magnetically induced current densities in the four-membered rings of Al4(2-) and Al4(4-) species have been calculated at the coupled-cluster singles and doubles (CCSD) level by applying the recently developed gauge-including magnetically induced current (GIMIC) method. The strength of the ring-current susceptibilities were obtained by numerical integration of the current densities passing through a cross section perpendicular to the Al4 ring. The GIMIC calculations support the earlier notion that Al4 (2-) with formally two pi electrons sustains a net diatropic ring current.

Infrared absorption spectrum of matrix-isolated noble-gas hydride molecules: fingerprints of specific interactions and hindered rotation.

Noble-gas hydride molecules with the general formula HNgY (Ng denotes noble-gas atom and Y denotes electronegative fragment) are usually prepared in solid noble gases. In many cases, the matrix-isolated HNgY molecules show a characteristic structure of the H-Ng stretching absorption: A close doublet as the main spectral feature and a weaker satellite at higher energy. This characteristic band structure is studied here for matrix-isolated HXeBr and HKrCl molecules.

Calculation of current densities using gauge-including atomic orbitals.

A method for calculating the various components of the magnetically induced current-density tensor using gauge-including atomic orbitals is described. The method is formulated in the framework of analytical derivative theory, thus enabling implementation at the Hartree-Fock self-consistent-field (HF-SCF) as well as at electron-correlated levels. First-order induced current densities have been computed up to the coupled-cluster singles and doubles level (CCSD) augmented by a perturbative treatment of triple excitations [CCSD(T)] for carbon dioxide and benzene and up to the full coupled-cluster singles, doubles, and triples (CCSDT) level in the case of ozone.