### Author Topic: calculation of end-end interaction energy nanotubes  (Read 13027 times)

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#### zh

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##### Re: calculation of end-end interaction energy nanotubes
« Reply #15 on: December 22, 2010, 08:59 »
No strict constraint between d1+d2 and d or (L1+L2). Maybe, d1+d2 >=8~10 in your case is sufficient.

#### Zexter

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##### Re: calculation of end-end interaction energy nanotubes
« Reply #16 on: December 23, 2010, 08:36 »
if a voltage is applied to the configuration through some electrode (left and right without gate)setup whether it would affect the minimum value of total energy.
whether the effect of gate voltage also have similar impact on it.
whether the total energy is a function of applied voltage.

#### Zexter

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##### Re: calculation of end-end interaction energy nanotubes
« Reply #17 on: December 23, 2010, 12:35 »
whether the effect of vaccum you described previously also to be taken into account when applying a bias to the left and right nanotube through some electrode.
But if that's the case then there is a problem with the contact between the electrode and my cnt (because of the terms d1 and d2 described).So what can I do
the vaccum thickness term (d1=4) makes the case of non-contact between the left electrode and the left capped cnt.
So what could be the possible structure if I want to know the effect of bias voltages on the potential energy of my system with varying distance.
« Last Edit: December 23, 2010, 12:42 by Zexter »

#### zh

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##### Re: calculation of end-end interaction energy nanotubes
« Reply #18 on: December 23, 2010, 17:17 »
whether the effect of vaccum you described previously also to be taken into account when applying a bias to the left and right nanotube through some electrode.
No necessary. The applied bias voltage or gate voltage could affect the interaction between the two capped ends of CNTs, i.e., at a finite bias voltage or gate voltage, the minimum distance between the capped ends of CNTs in a two-probe system may be different to the one in the case without applied voltage.

When studying the effect of applied bias voltage on the interaction between capped CNTs, you can employ the model in your previously attached image, the atomic configuration in that model is considered as the scattering region of a two-probe system, and the electrodes should be introduced. Follow a similar procedure to calculate the total energy of such two-probe system as a function of d (which is the distance between the two capped ends of CNTs) .
« Last Edit: December 23, 2010, 17:39 by zh »

#### Zexter

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##### Re: calculation of end-end interaction energy nanotubes
« Reply #19 on: December 24, 2010, 10:43 »
I am applying gate voltage through some metal dielectric setup as in attached figure.even in this configuration the vaccum level is neglected.But is there any constraint on thickness on the dielectric or metal here.
I am using
dielectric thickness (16,3.07914,9.49417)Angstrom with value 4
metallic (16,0.5,9.49417) Angstrom
with the gate being same above and below with -1V.
Can I study the effect of gate voltage alone without having the source and drain electrode defined.
« Last Edit: December 24, 2010, 10:47 by Zexter »

#### Zexter

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##### Re: calculation of end-end interaction energy nanotubes
« Reply #20 on: December 27, 2010, 10:00 »
Is there any procedure to compute iteratively the total energy by varying the distance between the nanotubes.

how to iteratively vary the distance between the nanotube within a particular range of values and compute the interaction energy for each separation distance.what's the procedure to do so

#### zh

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##### Re: calculation of end-end interaction energy nanotubes
« Reply #21 on: December 27, 2010, 11:58 »
In a two-probe system even with gate voltage, the electrodes must be included.

The distance between the nanotubes is defined a variable of a loop. Using the loop with this variable, one can perform the self-consistent calculation for a given value of the distance. The procedure is very similar to the one for calculating the total energies of O2 as a function of the distance between two O atoms:
http://quantumwise.com/documents/manuals/ATK-2008.10/chap.oxspin.html#sect1.oxspin.totalenergy

#### Zexter

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##### Re: calculation of end-end interaction energy nanotubes
« Reply #22 on: December 29, 2010, 13:56 »
Hi
I calculated the total energy of the structure with vaccum level at the edge of the central region as 0 and my gate biased at 6v,
left and right electrode at 0v
gate dielectric epsr=1
electrodes with 40 atoms 2.41 Angstroms
I have here attached my ever decreasing total energy curve. So what's strange with my system.Please help me in untangling this mystery.
my variation of distance is from 3to 4 Angstroms for which I get positive values of total energy
for 2.5 to 2.9 i get negative values, which is around -8500eV

So my questions are
1. What's the reason for positive values of total energy in the region 3 to 4.Is it right to get a positve energy value when the system is biased with the above configuration.
2. why my energy in 2.5 to 2.9 alone is negative.(I haven't tried below 2.5Angstroms)
3. whether applying  a bias would drive the energy to positive value of potential energy (which is unacceptable)
« Last Edit: January 11, 2011, 07:44 by Zexter »

#### Zexter

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##### Re: calculation of end-end interaction energy nanotubes
« Reply #23 on: January 11, 2011, 07:46 »
the minima in this configuration is hard to find.thecurve is ever decreasing and not changing the slope.

#### zh

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##### Re: calculation of end-end interaction energy nanotubes
« Reply #24 on: January 11, 2011, 07:50 »
1. What's the reason for positive values of total energy in the region 3 to 4.Is it right to get a positve energy value when the system is biased with the above configuration.
2. why my energy in 2.5 to 2.9 alone is negative.(I haven't tried below 2.5Angstroms)
Something may be wrong in your script file. Without taking look at your script file, one cannot find out the reasons.

#### Zexter

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##### Re: calculation of end-end interaction energy nanotubes
« Reply #25 on: January 11, 2011, 10:52 »
the files are here. I have each file made separately with varying the distance between them.
« Last Edit: January 17, 2011, 11:43 by Zexter »

#### Zexter

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##### Re: calculation of end-end interaction energy nanotubes
« Reply #26 on: January 18, 2011, 05:57 »
I am computing the total energy for each distance of separation being created separately.If the problem is with the script file then it should affect the separation distance of 2.5 to 3 Angstroms also.But the positive energy comes only for separation greater than 3Angstroms.Is there any other problem that can be attributed to this conflict.The files for separation distances 2.5,3,and 3.35 Angstroms are here.