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General Questions and Answers / Inconsistency in CalculateCurrent for different number of integration points
« on: March 18, 2009, 18:07 »
Hi,
I'm calculating current for a two probe system with graphene nano-ribbon electrodes.
I have converged sc files at .1V,.2V,.3V,.4V,.5V,.6V,.7V,.8V,.9V,1.0V.
At each bias, I have been calculating current using a different number of integration points over the energy. The default number of points is 100 and I also calculated current for 200, 400, 600, 800, and 1000 points as a check for consistency.
At lower bias, there is consistency across current calculations for different number of energy points. At higher bias, I'm getting some inconsistency. For example, at .8V I'm getting the following currents for different number of energy points:
100 Points
2.70322906734e-08 A
200 Points
6.15809652354e-09 A
400 Points
2.0376602094e-08 A
600 Points
2.67889424829e-08 A
800 Points
1.86633465855e-08 A
1000 Points
1.57990714177e-08 A
Furthermore, at a bias of .9V the currents have dropped a whole two orders of magnitude compared to .8V as seen from this data below:
100 Points
3.93849284671e-11 A
200 Points
3.90495735902e-10 A
400 Points
1.24586672635e-10 A
600 Points
2.48097024468e-10 A
800 Points
1.6369171909e-10 A
1000 Points
2.21587823888e-10 A
For lower bias up until a bias of .5V the I-V curve was monotonic increasing and there was more consistency in currents at a single bias. Clearly, at .9V the currents have dropped and are also inconsistent with the number of points.
Is there some explanation for this behavior? In another post, I recall reading that artificial scattering could occur if the electrode cell is not long enough in the z direction. Could artificial scattering be happening here at higher bias levels and not at lower bias levels? Note that, my electrode cells are 4 atoms thick (4.9 angstroms) and I have included this same number of atoms (thickness) for the screening layers on each electrode.
Any comments are appreciated,
Chris
I'm calculating current for a two probe system with graphene nano-ribbon electrodes.
I have converged sc files at .1V,.2V,.3V,.4V,.5V,.6V,.7V,.8V,.9V,1.0V.
At each bias, I have been calculating current using a different number of integration points over the energy. The default number of points is 100 and I also calculated current for 200, 400, 600, 800, and 1000 points as a check for consistency.
At lower bias, there is consistency across current calculations for different number of energy points. At higher bias, I'm getting some inconsistency. For example, at .8V I'm getting the following currents for different number of energy points:
100 Points
2.70322906734e-08 A
200 Points
6.15809652354e-09 A
400 Points
2.0376602094e-08 A
600 Points
2.67889424829e-08 A
800 Points
1.86633465855e-08 A
1000 Points
1.57990714177e-08 A
Furthermore, at a bias of .9V the currents have dropped a whole two orders of magnitude compared to .8V as seen from this data below:
100 Points
3.93849284671e-11 A
200 Points
3.90495735902e-10 A
400 Points
1.24586672635e-10 A
600 Points
2.48097024468e-10 A
800 Points
1.6369171909e-10 A
1000 Points
2.21587823888e-10 A
For lower bias up until a bias of .5V the I-V curve was monotonic increasing and there was more consistency in currents at a single bias. Clearly, at .9V the currents have dropped and are also inconsistent with the number of points.
Is there some explanation for this behavior? In another post, I recall reading that artificial scattering could occur if the electrode cell is not long enough in the z direction. Could artificial scattering be happening here at higher bias levels and not at lower bias levels? Note that, my electrode cells are 4 atoms thick (4.9 angstroms) and I have included this same number of atoms (thickness) for the screening layers on each electrode.
Any comments are appreciated,
Chris