584 research outputs found
CO adsorption on Pt induced Ge nanowires
Using density functional theory, we investigate the possible adsorption sites
of CO molecules on the recently discovered Pt induced Ge nanowires on Ge(001).
Calculated STM images are compared to experimental STM images to identify the
experimentally observed adsorption sites. The CO molecules are found to adsorb
preferably onto the Pt atoms between the Ge nanowire dimer segments. This
adsorption site places the CO in between two nanowire dimers, pushing them
outward, blocking the nearest equivalent adsorption sites. This explains the
observed long-range repulsive interaction between CO molecules on these Pt
induced nanowires.Comment: 12 pages, 10 figure
Models and Simulations in Material Science: Two Cases Without Error Bars
We discuss two research projects in material science in which the results
cannot be stated with an estimation of the error: a spectro- scopic
ellipsometry study aimed at determining the orientation of DNA molecules on
diamond and a scanning tunneling microscopy study of platinum-induced nanowires
on germanium. To investigate the reliability of the results, we apply ideas
from the philosophy of models in science. Even if the studies had reported an
error value, the trustworthiness of the result would not depend on that value
alone.Comment: 20 pages, 2 figure
Rationality: a social-epistemology perspective
Both in philosophy and in psychology, human rationality has traditionally been studied from an "individualistic" perspective. Recently, social epistemologists have drawn attention to the fact that epistemic interactions among agents also give rise to important questions concerning rationality. In previous work, we have used a formal model to assess the risk that a particular type of social-epistemic interactions lead agents with initially consistent belief states into inconsistent belief states. Here, we continue this work by investigating the dynamics to which these interactions may give rise in the population as a whole
Formation of Pt induced Ge atomic nanowires on Pt/Ge(001): a DFT study
Pt deposited onto a Ge(001) surface gives rise to the spontaneous formation
of atomic nanowires on a mixed Pt-Ge surface after high temperature annealing.
We study possible structures of the mixed surface and the nanowires by total
energy (density functional theory) calculations. Experimental scanning
tunneling microscopy images are compared to the calculated local densities of
states. On the basis of this comparison and the stability of the structures, we
conclude that the formation of nanowires is driven by an increased
concentration of Pt atoms in the Ge surface layers. Surprisingly, the atomic
nanowires consist of Ge instead of Pt atoms.Comment: 4 pages, 3 figure
Reply to 'Comment on "Extending Hirshfeld-I to bulk and periodic materials" '
The issues raised in the comment by T.A. Manz are addressed through the
presentation of calculated atomic charges for NaF, NaCl, MgO, SrTiO and
LaCeO, using our previously presented method for calculating
Hirshfeld-I charges in Solids [J. Comput. Chem.. doi: 10.1002/jcc.23088]. It is
shown that the use of pseudo-valence charges is sufficient to retrieve the full
all-electron Hirshfeld-I charges to good accuracy. Furthermore, we present
timing results of different systems, containing up to over atoms,
underlining the relatively low cost for large systems. A number of theoretical
issues is formulated, pointing out mainly that care must be taken when deriving
new atoms in molecules methods based on "expectations" for atomic charges.Comment: 7 pages, 2 Tables, 2 figure
Extending Hirshfeld-I to bulk and periodic materials
In this work, a method is described to extend the iterative Hirshfeld-I
method, generally used for molecules, to periodic systems. The implementation
makes use of precalculated pseudo-potential based charge density distributions,
and it is shown that high quality results are obtained for both molecules and
solids, such as ceria, diamond, and graphite. The use of such grids makes the
implementation independent of the solid state or quantum chemical code used for
studying the system. The extension described here allows for easy calculation
of atomic charges and charge transfer in periodic and bulk systems.Comment: 11 pages, 4 Tables, 5 Figures, pre-referee draft only, much extended
post referee version only available at publishe
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