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E.F. Sheka
N D increases from 31 e to 46 e and 54 e, respectively. Both findings evidence an
undoubted strengthening of the odd electron correlation caused by the chemicallystimulated deformation of the carbon skeleton.
Yet another evidence of the deformation effect is presented in Fig. 15.13. The figure shows the redistribution of unpaired electrons density over the skeleton atoms
caused by the deformation. As seen in the figure, the skeleton electron-density image greatly changes when the electron correlation becomes stronger (draw attention
on a large vertical scale of plottings presented in the top figure). Consequently, if observed by HRTEM, the basket-like skeleton might have look much brighter than the
canopy-like one and especially than the least bright pristine molecule. In view of the
finding, it is naturally to suggest that raised above the substrate and deformed areas
of graphene in the form of bubbles, found in a variety of shapes on different substrates [78, 79], reveal peculiar electron-density properties just due to the stretching
deformation that results in strengthening the odd electron correlation. Small (5, 5)
NGr molecule presented in Fig. 15.13 cannot pretend to simulate the picture observed for micron bubbles, but it exhibits the general trend that might take place in
bubbles, as well. In view of the obvious strengthening of the odd electron correlation
caused by the deformation, this explanation looks more natural than that proposed
from the position of an artificial ‘gigantic pseudo-magnetic field’ [78].
A considerable decreasing of the magnetic constants J stimulated by the deformation allows for suggesting a peculiar magnetic behaviour of the deformed
graphene regions, such as, say, bubbles, stimulated by both their size and curvature. The two parameters obviously favour decreasing in the constant values thus
promoting the appearance of magnetic response localized in the bubble regions.
Besides the formation of bubbles caused by ultrastrong adhesion of graphene
membranes to different substrates [80], the dynamic deformation of graphene can
be caused by the application of the external stress. The quantum molecular theory suggests considering the graphene molecule deformation and rupture in terms
of a mechanochemical reaction [81–83]. The quantum chemical realization of the
approach is based on the coordinate-of-reaction concept for the purpose of introducing a mechanochemical internal coordinate (MIC) that specifies the deformational
mode. The related force of response is calculated as the energy gradient along the
MIC while the atomic configuration is optimized over all other coordinates under
the MIC constant-pitch elongation. When applied to the description of the deformation of both (5, 5) NGr [81, 82] and (5, 5) NGra [83] molecules under uniaxial
tension, the calculations highlighted a pronounced changing in the number of effectively unpaired electrons N D of the sample in due course of its deformation. As
shown, the changing is different when the deformation occurs either along or normal
to the chains of C–C bonds. However, in all cases the changing is quite significant
pointing to a considerable strengthening of odd electron correlation due to changes
in interatomic spacings. A detailed consideration of a possible regulating mission of
the stress with respect to the enhancement of chemical reactivity of carbon atoms
and magnetic behaviour of the loaded sample obviously deserves a further thorough
study.
E.F. Sheka
N D increases from 31 e to 46 e and 54 e, respectively. Both findings evidence an
undoubted strengthening of the odd electron correlation caused by the chemicallystimulated deformation of the carbon skeleton.
Yet another evidence of the deformation effect is presented in Fig. 15.13. The figure shows the redistribution of unpaired electrons density over the skeleton atoms
caused by the deformation. As seen in the figure, the skeleton electron-density image greatly changes when the electron correlation becomes stronger (draw attention
on a large vertical scale of plottings presented in the top figure). Consequently, if observed by HRTEM, the basket-like skeleton might have look much brighter than the
canopy-like one and especially than the least bright pristine molecule. In view of the
finding, it is naturally to suggest that raised above the substrate and deformed areas
of graphene in the form of bubbles, found in a variety of shapes on different substrates [78, 79], reveal peculiar electron-density properties just due to the stretching
deformation that results in strengthening the odd electron correlation. Small (5, 5)
NGr molecule presented in Fig. 15.13 cannot pretend to simulate the picture observed for micron bubbles, but it exhibits the general trend that might take place in
bubbles, as well. In view of the obvious strengthening of the odd electron correlation
caused by the deformation, this explanation looks more natural than that proposed
from the position of an artificial ‘gigantic pseudo-magnetic field’ [78].
A considerable decreasing of the magnetic constants J stimulated by the deformation allows for suggesting a peculiar magnetic behaviour of the deformed
graphene regions, such as, say, bubbles, stimulated by both their size and curvature. The two parameters obviously favour decreasing in the constant values thus
promoting the appearance of magnetic response localized in the bubble regions.
Besides the formation of bubbles caused by ultrastrong adhesion of graphene
membranes to different substrates [80], the dynamic deformation of graphene can
be caused by the application of the external stress. The quantum molecular theory suggests considering the graphene molecule deformation and rupture in terms
of a mechanochemical reaction [81–83]. The quantum chemical realization of the
approach is based on the coordinate-of-reaction concept for the purpose of introducing a mechanochemical internal coordinate (MIC) that specifies the deformational
mode. The related force of response is calculated as the energy gradient along the
MIC while the atomic configuration is optimized over all other coordinates under
the MIC constant-pitch elongation. When applied to the description of the deformation of both (5, 5) NGr [81, 82] and (5, 5) NGra [83] molecules under uniaxial
tension, the calculations highlighted a pronounced changing in the number of effectively unpaired electrons N D of the sample in due course of its deformation. As
shown, the changing is different when the deformation occurs either along or normal
to the chains of C–C bonds. However, in all cases the changing is quite significant
pointing to a considerable strengthening of odd electron correlation due to changes
in interatomic spacings. A detailed consideration of a possible regulating mission of
the stress with respect to the enhancement of chemical reactivity of carbon atoms
and magnetic behaviour of the loaded sample obviously deserves a further thorough
study.