417 research outputs found
Hollywood Free Paper, May 5 1970
https://digitalcommons.fuller.edu/hollywoodfreepaper/1014/thumbnail.jp
Hollywood Free Paper, March 24 1970
https://digitalcommons.fuller.edu/hollywoodfreepaper/1011/thumbnail.jp
Hollywood Free Paper, April 7 1970
https://digitalcommons.fuller.edu/hollywoodfreepaper/1012/thumbnail.jp
Hollywood Free Paper, September 3 1970
https://digitalcommons.fuller.edu/hollywoodfreepaper/1022/thumbnail.jp
Molecular structures and vibrations of neutral and anionic CuOx (x = 1-3,6) clusters
We report equilibrium geometric structures of CuO2, CuO3, CuO6, and CuO
clusters obtained by an all-electron linear combination of atomic orbitals
scheme within the density-functional theory with generalized gradient
approximation to describe the exchange-correlation effects. The vibrational
stability of all clusters is examined on the basis of the vibrational
frequencies. A structure with Cs symmetry is found to be the lowest-energy
structure for CuO2, while a -shaped structure with C2v symmetry is the most
stable structure for CuO3. For the larger CuO6 and CuO clusters, several
competitive structures exist with structures containing ozonide units being
higher in energy than those with O2 units. The infrared and Raman spectra are
calculated for the stable optimal geometries. ~Comment: Uses Revtex4, (Better quality figures can be obtained from authors
Electron affinities of the first- and second- row atoms: benchmark ab initio and density functional calculations
A benchmark ab initio and density functional (DFT) study has been carried out
on the electron affinities of the first- and second-row atoms. The ab initio
study involves basis sets of and quality, extrapolations to
the 1-particle basis set limit, and a combination of the CCSD(T), CCSDT, and
full CI electron correlation methods. Scalar relativistic and spin-orbit
coupling effects were taken into account. On average, the best ab initio
results agree to better than 0.001 eV with the most recent experimental
results. Correcting for imperfections in the CCSD(T) method improves the mean
absolute error by an order of magnitude, while for accurate results on the
second-row atoms inclusion of relativistic corrections is essential. The latter
are significantly overestimated at the SCF level; for accurate spin-orbit
splitting constants of second-row atoms inclusion of (2s,2p) correlation is
essential. In the DFT calculations it is found that results for the 1st-row
atoms are very sensitive to the exchange functional, while those for second-row
atoms are rather more sensitive to the correlation functional. While the LYP
correlation functional works best for first-row atoms, its PW91 counterpart
appears to be preferable for second-row atoms. Among ``pure DFT'' (nonhybrid)
functionals, G96PW91 (Gill 1996 exchange combined with Perdew-Wang 1991
correlation) puts in the best overall performance. The best results overall are
obtained with the 1-parameter hybrid modified Perdew-Wang (mPW1) exchange
functionals of Adamo and Barone [J. Chem. Phys. {\bf 108}, 664 (1998)], with
mPW1LYP yielding the best results for first-row, and mPW1PW91 for second-row
atoms. Indications exist that a hybrid of the type mPW1LYP +
mPW1PW91 yields better results than either of the constituent functionals.Comment: Phys. Rev. A, in press (revised version, review of issues concerning
DFT and electron affinities added
Transition-metal dimers and physical limits on magnetic anisotropy
Recent advances in nanoscience have raised interest in the minimum bit size
required for classical information storage, i.e. for bistability with
suppressed quantum tunnelling and energy barriers that exceed ambient
temperatures. In the case of magnetic information storage much attention has
centred on molecular magnets[1] with bits consisting of ~ 100 atoms, magnetic
uniaxial anisotropy energy barriers ~ 50 K, and very slow relaxation at low
temperatures. In this article we draw attention to the remarkable magnetic
properties of some transition metal dimers which have energy barriers
approaching ~ 500 K with only two atoms. The spin dynamics of these ultra small
nanomagnets is strongly affected by a Berry phase which arises from
quasi-degeneracies at the electronic Highest Occupied Molecular Orbital (HOMO)
energy. In a giant spin-approximation, this Berry phase makes the effective
reversal barrier thicker. [1] Gatteschi, D., Sessoli, R. & Villain, J.
Molecular Nanomagnets. (Oxford, New York 2006).Comment: 14 pages, 1 figur
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