QuantumATK Forum
QuantumATK => General Questions and Answers => Topic started by: Zexter on December 18, 2010, 05:44
-
Hi
I just need to calculate the tip tip interaction between two cappped cnt.I have a capped structure of the cnt. So if I need to calculate the interaction between the nanotube is it enough to select the total energy alone in my calculation. I need only the interaction potential between the two
I have only one capped cnt. how to make a mirror image of the same cnt so that their caps face each other. Any help in the procedure to do so would be helpful. Since translating the cnt in builder is not helpful as when the file is saved and reopened the untranslated structure peeks out.
-
Hi
If i wanted to calculate interaction energy between the two capped nanotube is it enough to compute the difference between the total energy by varying the distance between them.
-
Yes, the way mentioned by you will work if the size of your supercell for a two capped nanotube is large enough.
-
can you please tell me the procedure to vary the distance between the nanotubes iteratively and to compute the energy according to the calculator defined for each iteration. I have a (5,5)nanotube with 5 repetitions making a structure with capped ends to 137 atoms. So would it be enough for your supercell stuff? ??? ??? the two capped nanotubes make around 2*137 atoms.Whether I want to reduce the atom count or proceed with the same structure
-
whether the potential energy of the capped nanotube system plotted with respect to distance of separation between the two nanotube would give the potential energy minima of the system ???
-
whether the potential energy of the capped nanotube system plotted with respect to distance of separation between the two nanotube would give the potential energy minima of the system ???
Yes, it does.
-
ok. the minima in the potential energy curve with distance give the potential energy minima. But I can have only the total energy of the system(the capped nanotubes) with me . So whether the total energy in this case is equal to the potential energy or else I want select some other option in the analysis part :-\ :-\
how the total energy is equal to the potential energy in this case ???
-
Usually, the potential energy curve means the total energy of a system with respect to a distance, e.g. the distance between two nanotubes in your case. In other word, the term of "potential energy" is improperly used in your question.
To obtain the interaction energy between two capped CNTs, one may follow the procedure used to calculate the total energy of O2 as a function of the distance between two O atoms:
i) assume that the distance between two capped CNTs is d;
ii) calculate the total energies (E_tot) of two capped CNTs with different values of d;
iii) calculate the total energies of each capped CNTs, separately. assume that they are E_tot(1) and E_tot(2), respectively;
iii) from the minimum energy (E_min) in the curve of E_tot vs d, the interaction energy will be E_min - E_tot(1) - E_tot(2).
-
Whether the same procedure adapted to calculate the interaction between the concentric walls of the double walled nanotube is followed even to calculate the in plane interaction between two capped cnt each one is single walled ???.
What's the reason to calculate the energy of the capped cnt's separately ???.
I have attached the image of such a kind here ::).
-
For the atomic configuration shown in your attached image, it is one CNT with two caps due to the periodicity along the c direction. To simulate the interaction between two CNTs each with one cap, a second vacuum layer is needed to be introduced in the c direction. In this case, for each CNT one of its end is capped and the other one is open. To simulate the interaction between two CNTs each with two caps at the ends, a second vacuum layer is also needed.
-
could you please tell me the why a vaccum layer has to be introduced and the procedure to introduce the same in my code.
What's the role played by vaccum layer and its effect here ???
If I am not dfining the vaccum layer what errors would result :-\
the c direction you are specifying is the z direction here. So if I plot the distance vs total energy of a system as above, Is the curve is wrong 8) even if I followed your procedure described in the previous posts to get the values.
-
The vacuum layer can be introduced by making the lattice constant c larger than the the length of CNT.
In the last reply, it is clearly said that the model built in your attached image corresponds to one CNT with two caps at the ends. That model cannot be used to simulate the interaction between two CNTs.
-
Sorry I am not getting the lattice constant c. How can be it be greater than CNT length which would be on a much larger scale.
So if my model is wrong then give a procedure to get the interaction between the structure of a similar kind
My theme is to get the interaction between two cnts of same type armchair (n,n) on their capped end side.
-
A schematic configuration for the simulation of interaction between two CNTs is shown in my attached image.
Using this model, the interaction energy between two CNTs each with one cap at the end can be obtained by calculating the total energy of such configuration as a function of d (i.e., the distance between two caps of CNTs) or c (i.e., the lattice constant along the c direction since c = d1+L1+d+L2+d2, as shown in the image.). Here the vacuum thickness d1+d2 should be large enough.
-
fine. whether d1 and d2 must be large enough than d or d1 and d2 greater than l1 and l2. what is the constraint you meant
-
No strict constraint between d1+d2 and d or (L1+L2). Maybe, d1+d2 >=8~10 in your case is sufficient.
-
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.
-
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. ::)
-
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) .
-
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.
-
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 ???
-
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 (http://quantumwise.com/documents/manuals/ATK-2008.10/chap.oxspin.html#sect1.oxspin.totalenergy)
-
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 :o :o :o
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)
-
the minima in this configuration is hard to find.thecurve is ever decreasing and not changing the slope.
-
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.
-
the files are here. I have each file made separately with varying the distance between them.
-
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.