Messages

46

General Questions and Answers / Re: Why more difficult to converge by using ATK2011.2.2?

« on: May 11, 2011, 16:45 »

In other words, we will use (contour_type=Left) at the negative bias voltage?

Exactly

However, what is the DoubleContourIntegralParameters used for ?(It is Poor convergence)

Are you saying why SCF convergence with double contour gets worse if there are bound states within bias window?
If so, I'm sorry that I don't have clear answer about it.
I've not understood the property of the formalism used for weighting scheme perfectly yet
http://www.quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/ref.doublecontourintegralparameters.html

So please note that even if there are bound states within bias window and double contour is used, SCF would converge well in some cases.
But there've also been the case that SCF can't converge due to it in my experience.
In such case, I could overcome the issue by using single contour.
And at the same time I did the two type of calculation (contour_type=Left, contour_type=Right), consequently I obtained the different electronic structure.
This is the direct evidence that there are indeed bound states within bias window.
 

47

General Questions and Answers / Re: Why more difficult to converge by using ATK2011.2.2?

« on: May 11, 2011, 14:04 »

Whether only change DoubleContourIntegralParameters to SingleContourIntegralParameters?

Yes, and if you want to include bound states within bias window in density matrix, you should set as "SingleContourIntegralParameters(contour_type=Right)".
(In the case of that a left voltage is higher than a right voltage)

48

General Questions and Answers / Re: Why more difficult to converge by using ATK2011.2.2?

« on: May 11, 2011, 12:12 »

Poor convergence in ATK 11.2.2 might come from bound states within bias window.
How about using single contour instead of double contour?

49

General Questions and Answers / Re: silicon nanowire bandgap query

« on: May 10, 2011, 15:28 »

I can't check your structure now but it's expected that the bare Si nanowire you prepared would be something wrong.
You should prepare a bare Si nanowire in which all Si-Si bond length are about 2.35angstrom in order to achieve proper sp3 passivation with the script.

50

General Questions and Answers / Re: Co or Ni electrode

« on: May 10, 2011, 08:54 »

Probably you can get proper results with such a setting

51

General Questions and Answers / Re: Thermal conductivity of one dimensional structures

« on: May 10, 2011, 08:51 »

Current version of ATK can only calculate thermal conductivity derived from coherent electron transport.
In other words, thermal conductivity derived from diffusive electron transport or coherent/diffusive phonon transport can't be treated in principle in ATK calculation now.

52

General Questions and Answers / Re: Does the current calculation make sense if a valence band enter the bias window?

« on: May 10, 2011, 01:58 »

I  think in bulk material the valence electrons don't participate conduction

Actually, valence electrons also contribute conductivity in bulk semiconductor.
They usually are described as a hole.

53

Scripts, Tutorials and Applications / Re: sp3-passivation with H for bare Si nanorod

« on: May 9, 2011, 03:12 »

Dear everyone,

I've made another version of the script, which enables one to do sp3 passivation of Silicon nanowire.
"nanowire" in the above sentence means that the structure has periodicity along z direction.

The usage is as follows:
1. prepare bare Si nanowire like "bare_sinw110.py",
2. launch Custom Builder,
3. Drop "passivate_sp3_2.py" onto "Drop your builder..." in the Custom Builder window,
4. Drop "bare_sinw110.py" onto "Drop unpassivated system here".

54

General Questions and Answers / Re: Reg. Conductance in Tutorial

« on: May 6, 2011, 04:23 »

I agree with Anders's consideration and let me make a supplementary statement.
Twisting nano-ribbon breaks the periodicity of the electronic structure, that leads to the collapse of ballistic transport.
But its influence against transport is relatively small, that means twisting does not affect drastically the sp2 bonding nature of Carbon.

55

General Questions and Answers / Re: Calculation the transport properties of graphene

« on: May 6, 2011, 04:06 »

but the properies look like nanoribbon, with quantized transmission spectrum

I guess that your transmission spectrum is step-like but the values are not integer.
Is this right?
If so, your calculation is reasonable, graphene should have such a feature.

I think over 50 angstroms is too long and you can reduce the size along z direction to 7-10 angstroms.
(Maybe even the primitive cell size is OK, I'm not sure because I don't know the detailed algorithm though...)

56

General Questions and Answers / Re: silicon nanowire bandgap query

« on: May 3, 2011, 13:11 »

for changing the bond length I want to mention Si-Si bond.

Perhaps you can make it by the following steps:
1. drop bare silicon nanowire onto Builder,
2. switch coordinate type to fractional,
3. change the unit cell size against x or y direction.

57

General Questions and Answers / Re: Current as a function of bias voltage sweep

« on: May 3, 2011, 13:02 »

Can you please provide me the script for the same curves you've shown in the fig.?

The example is as follows:
#---------------------------------------------------
bias_voltage = numpy.linspace(0.0,1.0,6)
current = []
for vb in bias_voltage:
    transmission_spectrum = nlread('gnr_IV.nc', object_id="Transmission"+str(vb))[0]
    current += [transmission_spectrum.current()]

print "-"*50
print "Bias Voltage [V]","\t","Current [nA]"
print "-"*50
for vb,i in zip(bias_voltage,current):
    print vb,"\t",i.inUnitsOf(Ampere)*(10**9)
#---------------------------------------------------

58

General Questions and Answers / Re: silicon nanowire bandgap query

« on: May 3, 2011, 12:35 »

Please let me know the script to do the Hydrogen passivation of dangling bonds

I've made the script to do it with Custom Builder but it's at my office now.
My office is closed until 8th May that's why I will able to give it to you next week.

what should I do for changing the bond length along X and Y direction.

Which do you mention, Si-H bond or Si-Si bond?

59

General Questions and Answers / Re: Current as a function of bias voltage sweep

« on: April 28, 2011, 08:08 »

Dear jai,

I'd like to give you the procedure to obtain I-V curve as follows:

1. launch VNL,
2. execute "gnr_IV.py" with Job manager,
3. launch Custom Analyzer,
4. Choose Analyzers/I-V curve from the menu,
5. Drop "gnr_IV.nc" onto "Drop file here",

After doing the procedure, you can obtain the result like "custom_analyzer.PNG"

60

General Questions and Answers / Re: silicon nanowire bandgap query

« on: April 27, 2011, 02:12 »

I've figured it out that the passivation of dangling bonds in the Si nanowire is incomplete.
That's why you can't obtain proper result with "silicon_wire-1_modified2.py".
Sorry for it.

I modified the script again and confirmed that reasonable band structure can be obtained.
Could you try  "silicon_wire-1_modified3.py" ?