Activity Report 2010 - CNRS

8 – NANOMODELING,
THEORY & SIMULATION
Theory and simulation concerns about 50
permanent researchers within the
Nanosciences Foundation community.
Theorists aim at developing new concepts
and new tools while nurturing a strong
coupling with experimentalists in
Grenoble. This strong synergy has been
supported and significantly improved by
the Nanosciences Foundation.
Several important scientific themes have
benefited from the Foundation actions:
electronic properties, thermal properties,
growth patterning and structure. The
Foundation had also enhanced the
collaboration of simulation specialists
through the NanoSTAR project.
Electronic properties
RTRA Project 2007: NanoSTAR
Coordinator: Valerio OLEVANO (Institut
Néel).
PhD students: Bhaarathi NATARAJAN and
Omid FAIZY NAMARVAR
One of the two pillars of the NanoSTAR
project deals with theoretical
spectroscopy developments and their
specific applications to nanomaterials and
molecules. Bhaarathi NATARAJAN’s thesis
work is focused on the development of
new approximations for the exchangecorrelation
(xc) kernel of time-dependent
density-functional theory in order to
explicitly include double excitations; and
as second task, the implementation of
such developments in a time-dependent
density-functional theory code relying on
a new basis set, that on the wavelets.
These developments will improve the
treatment of photochemical reactions
which are at the heart of excitonic
devices in particular for photovoltaic
applications. In order to describe
photoreactions by direct simulation one
particular challenge is the description of
the so-called conical intersection. These
intersections between the fundamental
state S0 and the excited state S1 are
seen as the photochemical analogue of
the transition state in thermal reactions.
(Figure 1) The contribution of the team
is an introduction of a spin-flip method.
Fig. 1: Caption of a conical intersection. The
graph represents the energy of the
fundamental state S0 and the excited state S1
in the configuration space obtained by
different numerical methods.
The other research line at the basis of the
NanoSTAR project is quantum transport
in nanodevices. This approach focuses on
applications and methodological
developments in general frameworks
such as the Landauer-Buttiker or the
Kubo-Greenwood. These techniques are
applied to interesting new systems like
graphene nanoribbons in presence also of
defects and functionalisation. The work is
carried out in collaboration by the Léti,
INAC/SPSMS and Institute NEEL.
Fig. 2: A methodology has been developed to
treat the effect of contact resistance. This has
been applied to short graphene nanoribbons
connected to half graphene planes. Fabry
Perot oscillations of the conductance, due to
contact resistance, are predicted for armchair
(up) and zig-zag (down) nanoribbons.
The project also aims at developing new
methodologies for transport of excitons in
a given material. The methodology,
which is adapted to small excitons, such
as those found in organic semiconductors
for example, is an extension of the
methodology which has been highly
successful for diffusion and conduction of
electrons.
FURTHER READING:
CONTACTS
Didier MAYOU
didier.mayou@grenoble.cnrs.fr
Tel: +33 4 76 88 74 66
Gilles LECARVAL
gilles.lecarval@cea.fr
Tel: +33 4 38 78 54 62
SCIENTIFIC REPORT
Phys. Chem. Chem. Phys. 12, 12811
(2010)
Assessment of noncollinear spin-flip
Tamm-Dancoff approximation timedependent
density-functional theory
for the photochemical ring-opening of
oxirane
Nanoresearch 3, 288 (2010)
Quantum Transport Properties of
Chemically
Functionalized Long Semiconducting
Carbon Nanotubes
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