42,258 research outputs found
Towards standard methods for benchmark quality ab initio thermochemistry --- W1 and W2 theory
Two new schemes for computing molecular total atomization energies (TAEs)
and/or heats of formation () of first-and second-row
compounds to very high accuracy are presented. The more affordable scheme, W1
(Weizmann-1) theory, yields a mean absolute error of 0.30 kcal/mol and includes
only a single, molecule-independent, empirical parameter. It requires CCSD
(coupled cluster with all single and double substitutions) calculations in
and basis sets, while CCSD(T) [i.e. CCSD with a
quasiperturbative treatment of connected triple excitations] calculations are
only required in and basis sets. On workstation computers and
using conventional coupled cluster algorithms, systems as large as benzene can
be treated, while larger systems are feasible using direct coupled cluster
methods. The more rigorous scheme, W2 (Weizmann-2) theory, contains no
empirical parameters at all and yields a mean absolute error of 0.23 kcal/mol,
which is lowered to 0.18 kcal/mol for molecules dominated by dynamical
correlation. It involves CCSD calculations in and basis sets
and CCSD(T) calculations in and basis sets. On workstation
computers, molecules with up to three heavy atoms can be treated using
conventional coupled cluster algorithms, while larger systems can still be
treated using a direct CCSD code. Both schemes include corrections for scalar
relativistic effects, which are found to be vital for accurate results on
second-row compounds.Comment: J. Chem. Phys., in press; text 30 pages RevTeX; tables 10 pages, HTML
and PostScript versions both included Reason for replacement: fixed typos in
Table II in proo
On Galois-Division Multiple Access Systems: Figures of Merit and Performance Evaluation
A new approach to multiple access based on finite field transforms is
investigated. These schemes, termed Galois-Division Multiple Access (GDMA),
offer compact bandwidth requirements. A new digital transform, the Finite Field
Hartley Transform (FFHT) requires to deal with fields of characteristic p, p
\neq 2. A binary-to-p-ary (p \neq 2) mapping based on the opportunistic
secondary channel is introduced. This allows the use of GDMA in conjunction
with available digital systems. The performance of GDMA is also evaluated.Comment: 6 pages, 4 figures. In: XIX Simposio Brasileiro de Telecomunicacoes,
2001, Fortaleza, CE, Brazi
An alternative theoretical approach to describe planetary systems through a Schrodinger-type diffusion equation
In the present work we show that planetary mean distances can be calculated
with the help of a Schrodinger-type diffusion equation. The obtained results
are shown to agree with the observed orbits of all the planets and of the
asteroid belt in the solar system, with only three empty states. Furthermore,
the equation solutions predict a fundamental orbit at 0.05 AU from solar-type
stars, a result confirmed by recent discoveries. In contrast to other similar
approaches previously presented in the literature, we take into account the
flatness of the solar system, by considering the flat solutions of the
Schrodinger-type equation. The model has just one input parameter, given by the
mean distance of Mercury.Comment: 6 pages. Version accepted for publication in Chaos, Solitons &
Fractal
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