2,109 research outputs found
Time-Dependent Transport Through Molecular Junctions
We investigate transport properties of molecular junctions under two types of
bias--a short time pulse or an AC bias--by combining a solution for the Green
functions in the time domain with electronic structure information coming from
ab initio density functional calculations. We find that the short time response
depends on lead structure, bias voltage, and barrier heights both at the
molecule-lead contacts and within molecules. Under a low frequency AC bias, the
electron flow either tracks or leads the bias signal (capacitive or resistive
response) depending on whether the junction is perfectly conducting or not. For
high frequency, the current lags the bias signal due to the kinetic inductance.
The transition frequency is an intrinsic property of the junctions.Comment: 5 pages, 9 figure
Intermolecular Effect in Molecular Electronics
We investigate the effects of lateral interactions on the conductance of two
molecules connected in parallel to semi-infinite leads. The method we use
combines a Green function approach to quantum transport with density functional
theory for the electronic properties. The system, modeled after a
self-assembled monolayer, consists of benzylmercaptane molecules sandwiched
between gold electrodes. We find that the conductance increases when
intermolecular interaction comes into play. The source of this increase is the
indirect interaction through the gold substrate rather than direct
molecule-molecule interaction. A striking resonance is produced only 0.3 eV
above the Fermi energy.Comment: 4 pages, 5 figure
Selection of non-regular fractional factorial designs when some two-factor interactions are important
Introduction: Non-regular two-level fractional factorial designs, such as Placket-Burman designs, are becoming popular choices in many areas of scientific investigation due to their run size economy and flexibility. The run size of non-regular two-level factorial designs is a multiple of 4. They fill the gaps left by the regular two-level fractional factorial designs whose run size is always a power of 2 (4, 8, 16, 32, ...). In non-regular factorial designs each main effect is partially confounded with all the two-factor interactions not involving itself. Because of this complex aliasing structure, non-regular factorial designs had not received sufficient attention until recently. ... In practical applications of non-regular designs, it is often in the case that some of the two-factor interactions are important and need to be estimated in addition to the main effects. In this article, we consider how to select non-regular two-level fractional factorial designs when some of the two-factor interactions are presumably important. We propose and study a method to select the optimal non-regular two-level fractional factorial designs in the situation that some of the two-factor interactions are potentially important. We then discuss how to search for the best designs according to this method and present some results for the Plackett-Burman design of 12 runs.Includes bibliographical references
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