Electric response properties of a confined gas of independent particles acted upon by a direct current electric field

Exact results for linear and nonlinear electric response properties of a non-interacting ensemble of charged particles, confined within an impenetrable box and subjected to a static, homogeneous electric field, are derived and discussed. Received: 16 September 1999 / Accepted: 3 February 2000 / Published online: 5 June 2000     

Relativistic calculations on thallium hydride

The spectroscopic parameters of the ground state of thallium hydride are obtained using the four-component relativistic Dirac–Coulomb–Gaunt–coupled-cluster wave function with single and double excitations and an estimated triples correction method. Core correlation effects make the bond weaker but have little effect on the bond length. Inclusion of the distance dependence of the Gaunt part of the two-electron Breit interaction has an opposite but smaller effect on these properties. Received: 8 September 2000 / Revised version: 5 October 2000 / Published online: 21 December 2000     

Recombination of silicon ions by electron capture from atomic hydrogen and helium

 Ab initio potential-energy curves and coupling matrix elements of the Σ and Π molecular states involved in the collision of the Si²⁺, Si³⁺ and Si⁴⁺ multicharged ions on atomic hydrogen and helium have been determined by means of configuration interaction methods. The total and partial electron capture cross sections have been determined using a semiclassical or a quantal approach in the 0.002–0.1 au velocity range. A detailed comparison with very recent theoretical and experimental rate coefficient results is made. Received: 14 September 1999 / Accepted: 3 February 2000 / Published online: 2 May 2000     

Determination of the diffusion coefficient of water into atelocollagen type I thin films by attenuated total reflection Fourier transform infrared spectroscopy

 The diffusion coefficient of water into thin polymer layers of glutar aldehyde cross-linked atelocollagen type I matrix (sample 1, the typical layer thickness was about 0.065 × 10⁻³ m) at 23 °C was 1.142 × 10⁻¹⁰ m² s⁻¹. At twice the concentration of the cross-linking agent (sample 2) the diffusion coefficient was 2.795 × 10⁻¹⁰ m² s⁻¹. This increase was attributed to the more ordered morphology and the creation of ordered microvoids in the film. A larger surface area is then available for the transport of diffusing molecules, allowing a higher penetration rate of the solvent. Received: 11 January 2000/Accepted: 6 May 2000     

A density functional theory study of the chemoselectivity and regioselectivity of the domino cycloaddition reactions of nitroalkenes with substituted alkenes

The chemoselectivity and regioselectivity of the domino intermolecular [4 + 2]/[3 + 2] cycloaddition reactions of nitroalkenes with substituted alkenes, vinyl ethers as electron-rich alkenes and vinyl ketones as electron-poor alkenes, have been studied using density functional theory (DFT) methods with the B3LYP functional and the 6-31G^* basis set. These domino processes comprise two consecutive cycloaddition reactions: the first one is an intermolecular [4 + 2] cycloaddition of the vinyl ether to the nitroalkene to give a nitronate intermediate, which then affords the final nitroso acetal adduct through an intermolecular [3 + 2] cycloaddition reaction with the vinyl ketone. The two consecutive cycloadditions present total chemoselectivity and ortho regioselectivity. While first [4 + 2] cycloaddition reaction takes place along the attack of the electron-rich alkene to nitroalkene, the [3 + 2] one takes place along the attack of the electron-poor alkene to the corresponding nitronate intermediate. This DFT study is in complete agreement with the experimental results. Received: 16 September 1999 / Accepted: 3 February 2000 / Published online: 2 May 2000     

Analysis of the RGD sequence in protein structures: comparison to the conformations of the RGDW and DRGDW peptides determined by molecular dynamics simulations

Geometric properties of the RGD sequence in a data set of protein crystal and NMR structures deposited in the Protein Data Bank were examined to identify structural characteristics that are related to cell adhesion activity. Interatomic distances and dihedral angles are examined. These geometric measures are then used in an analysis of the conformations of the RGDW and _DRGDW peptides obtained from molecular dynamics simulations (Stote RH, et al. (2000) J Phys ChemB 104:1624). This analysis leads to the suggestion that differences in the accessible conformations contribute to the difference in biological activity between the RGDW and the _DRGDW peptides. Received: 15 August 2000 / Accepted: 4 October 2000 / Published online: 21 March 2001     

Relativistic Gaussian basis sets for the elements K – Uuo

A series of energy-minimized relativistic Gaussian basis sets for the elements with atomic numbers 19–118 is presented. The basis sets have been derived at the self-consistent field level as weighted average energies of the respective electronic configurations. A spherical Gaussian charge distribution has been used to model the nucleus. The basis sets are constructed as interleaving dual family sets with shared exponents within each family. The quality of the basis sets is better than double zeta. Received: 7 July 2000 / Accepted: 21 September 2000 / Published online: 21 December 2000     

Energy decomposition in the topological theory of atoms in molecules and in the linear combination of atomic orbitals formalism: a note

 It is shown that the molecular energy calculated at the self-consistent-field level can be strictly expressed as a sum of one- and two-atom energy components in the framework of Bader's topological theory of atoms in molecules (AIM). The expressions of our recent “chemical energy component analysis” can be obtained from the AIM ones as some linear combination of atomic orbitals mappings of the integrations over the atomic basins. Received: 15 June 2000 / Accepted: 4 October 2000 / Published online: 19 January 2001     

Dynamic light scattering of an ionic SDS micellar solution under an AC electric field

The phase separation behavior of near-critical ionic sodium-dodecyl-sulfate (SDS) micellar solution under a sinusoidal electric field was investigated by phase-contrast optical microscopy and by the small-angle dynamic light scattering method. The sinusoidal electric field significantly deformed the concentration domains and shifted the phase separation temperature. The autocorrelation function under a sinusoidal electric field was measured in the vicinity of a phase separation temperature range of 0.10 K < T_p – T < 0.97 K, where T_p – T is the temperature distance from the phase separation temperature in quiescent state T_p. The correlation function with an oscillatory part in the longer correlation time region was observed. The occurrence of the oscillatory mode, which depended on both the applied field frequency and the ambient temperature, indicates deformation of concentration fluctuation domains by dynamical coupling between the phase separation and the applied sinusoidal electric field. Received: 9 June 2000 Accepted: 31 August 2000     

Multicenter bonding within the AIM theory

This study reports the incorporation of recently proposed formalism for the detection and localization of multicenter bonding in molecules, the so-called generalized population analysis, into the framework of the atoms in molecules (AIM) theory. The reliability of this new approach is tested by direct numerical comparison of the values of multicenter bond indices derived from both the original and the AIM-generalized forms of the population analysis. Received: 1 June 2000 / Accepted: 11 October 2000 / Published online: 23 January 2001     

The mechanism of spin polarization in aromatic free radicals

 The spin-polarization mechanism in aromatic systems is analyzed with reference to the prototypical phenoxyl, cyclohexadienyl and benzyl radicals. In particular, a decomposition into “first-order” and “second-order” contributions is proposed, which helps to rationalize the different nature of the spin density for atoms in α or in β positions with respect to the radical center. The different weights of the two contributions are discussed on the basis of Hartree–Fock and density functional computations. Received: 17 September 1999 / Accepted: 3 February 2000 / Published online: 29 June 2000     

Microgravity experiments on colloidal crystallization of silica spheres in the presence of sodium chloride

 Rate coefficients (k) in the colloidal crystallization of monodispersed silica spheres in the presence of sodium chloride are studied in microgravity achieved by parabolic flights of an aircraft. Time-resolved reflection spectroscopy is made with a continuous circulating-type stopped-flow cell system. The k values decrease as the salt concentration increases both at 0 and 1 G and those in microgravity are smaller than those in normal gravity by 16% (maximum), especially in water and in the presence of a small amount of the salt lower than 2 × 10⁻⁶ mol/l. The rates in flight at 1 G are larger by 15% (maximum) compared with those at 1 G on the ground. The k values obtained at 0 G, 1 G in flight and 1 G on the ground agree excellently with each other for the suspensions with 3 × 10⁻⁶ and 4 × 10⁻⁶ mol/l sodium chloride. Disappearance of the downward diffusion of spheres and no convection of the suspensions are important for retardation in microgravity. Received: 20 January 2000 Accepted: 9 March 2000     

Near-degeneracy corrections for second-order perturbation theory: comparison of two approaches

 We compare two approximate perturbation schemes which were developed recently to deal with the (quasi)degeneracy problem in many-body perturbation theory. We conclude that although the two methods were introduced on quite different theoretical grounds, their performances are quite similar, and present an improvement over traditional perturbation theory. Both methods are cheap in computation time, but cannot compete in accuracy with more sophisticated schemes such as complete-active-space perturbation theory or dressed particle theories. Received: 1 August 2000 / Accepted: 2 August 2000 / Published online: 19 January 2001     

Analytical Hartree–Fock wave functions for the atoms Cs to Lr

 Analytical approximations to Hartree–Fock wave functions are constructed using Slater-type functions for the ground states of all 49 neutral atoms from Cs (Z=55) to Lr (Z=103). The current compilation is more extensive and more accurate than previous ones. The wave functions are available upon request from the authors or from the Web page http://www.unb.ca/chem/ajit/download.htm on the Internet. Received: 6 December 1999 / Accepted: 29 February 2000 / Published online: 12 May 2000     

A theoretical investigation of (−)-deprenyl (selegiline) as a radical scavenger

The chemical reactions between (−)-deprenyl and ·OH or ·OOH were studied using molecular orbital theory, with N,N-dimethylpropargylamine as a model. (−)-Deprenyl was confirmed to be a good radical scavenger. The active site was the acetylenic part and ·OH- or ·OOH was trapped on either acetylenic carbon. The activation energies were about 10–20 kcal/mol. The resulting ·OH- or ·OOH-adducts, still radicals, trapped further radicals on the remaining carbon of the acetylenic part. The final double trapping products were at extraordinarily lower energy levels than the original reactants by 50–70 kcal/mol. The secondary transition states were not detected, suggesting that the reactions occurred at once or in a cascade. Some results with the model system were verified by the results with the real (−)-deprenyl system. Received: 6 October 1999 / Accepted: 5 March 2000 / Published online: 21 June 2000     

Spin-projected coupled-cluster theory with single and double excitations

Coupled-cluster (CC) theory including single (S) and double (D) excitations and carried out with a spin-unrestricted Hartree–Fock (UHF) reference wave function is free from S + 1 spin contamination as can be confirmed by an analysis of the expectation value of the spin operator, Ŝ ². Contamination by the S + 2 contaminant can be projected out by an approximate procedure (APCCSD) with a projection operator, P^, represented by the product of the spin annihilation operators ? _{s+ 1} and ?_s+2. The computational cost of such a projection scales with O(M ⁶) (M is the number of basis functions). The APCCSD energy obtained after annihilation of the S + 2 contaminant can be improved by adding triple (T) excitations in a perturbative way, thus leading to APCCSD(T) energies. For the 17 examples studied, the deviation of the UHF-CCSD(T) energies from the corresponding full configuaration interaction values is reduced from 4.0 to 2.3 mhartree on the average as a result of annihilating the S + 2 contaminant in an approximate way. In the case of single-bond cleavage, APCSSD leads to a significant improvement of the energy in the region where the bonding electrons recouple from a closed shell to an open shell singlet electron pair. Received: 13 April 2000 / Accepted: 12 July 2000 / Published online: 24 October 2000     

Excitation energies, electron affinities and ionization potentials of the transition metals V, Cr and Mn

 Configuration interaction calculations were carried out for neutral ground and excited states and positively and negatively ionized states of the V, Cr and Mn atoms. Energy convergence with respect to systematic expansion of both the one-electron and configuration bases was investigated for valence correlation. Contributions from core electrons to the differential correlation energies and relativistic effects were evaluated separately. Assuming additivity of these contributions, excitation energies, electron affinities and ionization potentials of the atoms were obtained. All calculated values were in excellent agreement with the observed values within a deviation of 0.056 eV except for the electron affinity of the V atom, which had a calculated value 0.110 eV larger than the experimental value. Received: 9 August 2000 / Accepted: 26 October 2000 / Published online: 3 April 2001     

Multireference perturbation CI IV. Selection procedure for one-electron properties

We present in this paper a modification of the selection procedure, within the CIPSI algorithm, specifically intended for the calculation of one-electron properties. In this new procedure the determinants are selected following their contribution to a certain one-electron property. As test cases we report the calculation of the electric dipole of carbon monoxide and of the hyperfine coupling constants of the CH₃ radical. Received: 20 August 2000 / Accepted: 2 October 2000 / Published online: 21 December 2000     

Coupling overall rotations with modal dynamics

 We consider a model for protein dynamics in which only certain collective, global motions are allowed. These directions are given by the slowest harmonics modes, as given in the reference frame of the protein. Furthermore, the latter is allowed to rotate and translate in response to interactions with other molecules. The model is obtained by projecting the (averaged) Newton equations onto this set of harmonic modes. We show that the subsequent homogenization of the time scales allows time steps one order of magnitude larger than the standard ones. This homogenization is also shown to be a necessary ingredient in order to get meaningful statistics of the trajectory. Received: 3 July 2000 / Accepted: 15 September 2000 / Published online: 21 December 2000     

Inexpensive and accurate predictions of optical excitations in transition-metal complexes: the TDDFT/PBE0 route

Time-dependent density functional theory (TDDFT) is applied to calculate vertical excitation energies of three representative transition metal complexes. The computational model (PBE0) is obtained by combining the Perdew-Burke-Erzenrhof (PBE) generalized gradient functional with a predetermined amount of exact exchange. Our results show that the TDDFT/PBE0 model represents a cheap and reliable tool for the computation of optical excitations for transition metal complexes. Received: 8 August 2000 / Accepted: 7 September 2000 / Published online: 23 November 2000