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Periodic Systems (periodic + system)

Distribution by Scientific Domains

Chemistry	62%
Engineering	37%

Selected Abstracts

Some solved problems of the periodic system of chemical elements

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 8 2010
W. H. Eugen Schwarz
Abstract Basic questions on the periodic system (PS) of chemical elements are still under discussion. Several common misconceptions will be resolved. The word "chemical element" comprises more than two concepts. The PS can be rationalized on a quantum chemical basis, namely with the aid of four concepts: (1) electron configurations of bonded atoms, (2) realistic sequences of orbital energies, (3) spatial extension of valence and Rydberg orbitals, and (4) energy gaps above the closed 1s2 and np6 shells (n = 2,6). The PS of known elements cannot be naively extrapolated. The common discussion of the PS in textbooks of general, inorganic, and physical chemistry needs revision. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]

Proton affinities of maingroup-element hydrides and noble gases: Trends across the periodic table, structural effects, and DFT validation

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2006
Marcel Swart
Abstract We have carried out an extensive exploration of the gas-phase basicity of archetypal neutral bases across the periodic system using the generalized gradient approximation (GGA) of the density functional theory (DFT) at BP86/QZ4P//BP86/TZ2P. First, we validate DFT as a reliable tool for computing proton affinities and related thermochemical quantities: BP86/QZ4P//BP86/TZ2P is shown to yield a mean absolute deviation of 2.0 kcal/mol for the proton affinity at 298 K with respect to experiment, and 1.2 kcal/mol with high-level ab initio benchmark data. The main purpose of this work is to provide the proton affinities (and corresponding entropies) at 298 K of the neutral bases constituted by all maingroup-element hydrides of groups 15,17 and the noble gases, that is, group 18, and periods 1,6. We have also studied the effect of step-wise methylation of the protophilic center of the second- and third-period bases. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1486,1493, 2006 [source]

Coupled-perturbed Hartree,Fock theory for quasi,one-dimensional periodic systems: Calculation of static and dynamic nonlinear optical properties of model systems

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2003
A. Martinez
Abstract An alternative method to solve the coupled-perturbed Hartree,Fock (CPHF) equations for infinite quasi,one-dimensional systems is presented. The new procedure follows a proposal made by Langhoff, Epstein, and Karplus to obtain perturbed wavefunctions free from arbitrary phase factors in each order of perturbation. It is based on the intermediate orthonormalization of the perturbed wavefunctions (which is different from the usual one) and a corresponding selection of the Lagrangian multipliers. In this way it is possible to incorporate the orthonormalization conditions into the set of CPHF equations. Moreover, a new, advantageous procedure to determine the derivatives of the wavefunction with respect to the quasimomentum k is presented. We report calculations of the dipole moment, the polarizability ,, and the first hyperpolarizability , for different polymers (poly-HF, poly-H2O, trans-polyacetylene, polyyne, and polycarbonitrile) for different frequencies. These results are extensively compared with oligomer calculations. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 251,268, 2003 [source]

Duality and eventually periodic systems

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 13 2005
M. Farhood
Abstract This paper employs semidefinite programming duality theory to develop new alternative linear matrix inequality (LMI) tools for eventually periodic systems. These tools are then utilized to rederive an important version of the Kalman,Yakubovich,Popov (KYP) Lemma for such systems, and further give new synthesis results. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Instabilities and bifurcations in lid-driven cavity flows

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003
Hendrik C. Kuhlmann Dr.
The three-dimensional flow of an incompressible Newtonian fluid in a rectangular slab is calculated numerically using a pseudo-spectral method. The fluid motion is driven by two facing sidewalls which can move in parallel or anti-parallel directions. Examples for bifurcations from two-dimensional to three-dimensional flows are given for spanwise periodic systems. For a comparison with previous experimental results rigid end walls are also considered. Differences between periodic and rigid end conditions are highlighted. [source]

Discrete tomography of planar model sets

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2006
Michael Baake
Discrete tomography is a well-established method to investigate finite point sets, in particular finite subsets of periodic systems. Here, we start to develop an efficient approach for the treatment of finite subsets of mathematical quasicrystals. To this end, the class of cyclotomic model sets is introduced, and the corresponding consistency, reconstruction and uniqueness problems of the discrete tomography of these sets are discussed. [source]