73,544 research outputs found
Core-valence correlations for atoms with open shells
We present an efficient method of inclusion of the core-valence correlations
into the configuration interaction (CI) calculations. These correlations take
place in the core area where the potential of external electrons is
approximately constant. A constant potential does not change the core electron
wave functions and Green's functions. Therefore, all operators describing
interaction of valence electrons and core electrons (the core part of
the Hartree-Fock Hamiltonian
, the correlation potential and
the screening of interaction between valence electrons by the core electrons
) may be calculated with all
valence electrons removed. This allows one to avoid subtraction diagrams
which make accurate inclusion of the core-valence correlations for
prohibitively complicated. Then the CI Hamiltonian for valence electrons is
calculated using orbitals in complete potential (the mean field
produced by all electrons); + are added to the CI
Hamiltonian to account for the core-valence correlations. We calculate
and using many-body perturbation theory in which
dominating classes of diagrams are included in all orders.
We use neutral Xe I and all positive ions up to Xe VIII as a testing ground.
We found that the core electron density for all these systems is practically
the same. Therefore, we use the same and to build
the CI Hamiltonian in all these systems (). Good agreement
with experiment for energy levels and Land\'{e} factors is demonstrated for all
cases from Xe I to Xe VIII.Comment: 13 pages, 5 figure
Assembly, Structure, and Reactivity of Cu\u3csub\u3e4\u3c/sub\u3eS and Cu\u3csub\u3e3\u3c/sub\u3eS Models for the Nitrous Oxide Reductase Active Site, Cu\u3csub\u3eZ\u3c/sub\u3e*
Bridging diphosphine ligands were used to facilitate the assembly of copper clusters with single sulfur atom bridges that model the structure of the CuZ* active site of nitrous oxide reductase. Using bis(diphenylphosphino)amine (dppa), a [CuI4(μ4-S)] cluster with N–H hydrogen bond donors in the secondary coordination sphere was assembled. Solvent and anion guests were found docking to the N–H sites in the solid state and in the solution phase, highlighting a kinetically viable pathway for substrate introduction to the inorganic core. Using bis(dicyclohexylphosphino)methane (dcpm), a [CuI3(μ3-S)] cluster was assembled preferentially. Both complexes exhibited reversible oxidation events in their cyclic voltammograms, making them functionally relevant to the CuZ* active site that is capable of catalyzing a multielectron redox transformation, unlike the previously known [CuI4(μ4-S)] complex from Yam and co-workers supported by bis(diphenylphosphino)methane (dppm). The dppa-supported [CuI4(μ4-S)] cluster reacted with N3–, a linear triatomic substrate isoelectronic to N2O, in preference to NO2–, a bent triatomic. This [CuI4(μ4-S)] cluster also bound I–, a known inhibitor of CuZ*. Consistent with previous observations for nitrous oxide reductase, the tetracopper model complex bound the I– inhibitor much more strongly and rapidly than the substrate isoelectronic to N2O, producing unreactive μ3-iodide clusters including a [Cu3(μ3-S)(μ3-I)] complex related to the [Cu4(μ4-S)(μ2-I)] form of the inhibited enzyme
A Cu\u3csub\u3e4\u3c/sub\u3eS Model for the Nitrous Oxide Reductase Active Sites Supported Only by Nitrogen Ligands
To model the (His)7Cu4Sn (n = 1 or 2) active sites of nitrous oxide reductase, the first Cu4(μ4-S) cluster supported only by nitrogen donors has been prepared using amidinate supporting ligands. Structural, magnetic, spectroscopic, and computational characterization is reported. Electrochemical data indicates that the 2-hole model complex can be reduced reversibly to the 1-hole state and irreversibly to the fully reduced state
Oblique-Basis Calculations for Ti
The spectrum and wave functions of Ti are studied in oblique-basis
calculations using spherical and SU(3) shell-model states. Although the results
for Ti are not as good as those previously reported for Mg, due
primarily to the strong spin-orbit interaction that generates significant
splitting of the single-particle energies that breaks the SU(3) symmetry, a
more careful quantitative analysis shows that the oblique-basis concept is
still effective. In particular, a model space that includes a few SU(3)
irreducible representations, namely, the leading irrep (12,0) and next to the
leading irrep (10,1) including its spin S=0 and 1 states, plus spherical
shell-model configurations (SSMC) that have at least two valence nucleons
confined to the orbit -- the SM(2) states, provide results that are
compatible with SSMC with at least one valence nucleon confined to the
orbit -- the SM(3) states.Comment: 3 pages, no figures, contribution to Computational and Group
Theoretical Methods in Nuclear Physics, Playa del Carmen, Mexico, February
18-21, 200
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