Messages

91

General Questions and Answers / Re: What dose DD mean in the log file

« on: October 18, 2017, 10:54 »

1) DD = density matrix on that specific atom.
2) yes, U/D means up/down components
3) see answer 1)

92

General Questions and Answers / Re: Penta-graphene nanoribbon

« on: October 18, 2017, 10:52 »

1) You should use the recipe on https://quantumwise.com/forum/index.php?topic=5329.msg23011#msg23011 to first create penta-graphene, then remove the appropriate C atoms  to create ribbon without repeating the cell.
2) Use the Coordinate Tools --> Custom Passivator with SP2 hybridization to passivate with only 1 H atom.

93

General Questions and Answers / Re: asking for the explanation of the IV curve

« on: October 18, 2017, 09:16 »

Depends on whether the device is physically stable at the IV point at which you find NDC.

94

General Questions and Answers / Re: spin polarized electrostatic difference potential

« on: October 18, 2017, 09:15 »

In addition: In newer versions one can specify which spin projection to plot in the 1D Projector, don't know how this works in ATK 13.8

95

General Questions and Answers / Re: Nanowire (001)

« on: October 18, 2017, 09:08 »

The (001) direction is completely equivalent to (100), and to (010). So just use the Nanowire Builder with the (100)  wire direction.

96

General Questions and Answers / Re: Value of current from iv self consisent file

« on: October 16, 2017, 08:03 »

You just retrieve that information from the IVCurve analysis object:
https://docs.quantumwise.com/manuals/Types/IVCurve/IVCurve.html

Code

ivcurve = nlread('XXX.nc', IVCurve)[-1]
biases = ivcurve.biases()
currents = ivcurve.currents()
import pylab
pylab.plot(biases, currents, 'bo-')
pylab.xlabel('Bias (Volt)')
pylab.ylabel('Current (Amps)')
pylab.show()

97

General Questions and Answers / Re: why is my density of states not smooth？

« on: October 16, 2017, 07:58 »

Gaussian broadening of the DOS is needed if you want it to be smooth. In the ATK Manuals you will find an example of how to plot the DOS using a Gaussian spectrum with e.g. 0.2 eV broadening:
https://docs.quantumwise.com/manuals/Types/DensityOfStates/DensityOfStates.html#usage-examples

98

General Questions and Answers / Re: Nanowire (001)

« on: October 16, 2017, 07:53 »

Select a primitive bulk configuration in the Stash, and use the Nanowire Builder to create a nanowire bulk with (100), (110), or (111) orientation. You should also decide on the NW radius and set the surface energy values such that their relative sizes match. After that, you may want to repeat the NW configuration along the z-direction.

99

General Questions and Answers / Re: Gilbert damping of Co2FeAl

« on: October 16, 2017, 07:46 »

From a scientific point of view, how do you plan to compute the Gilbert damping constant? Which equation, etc. ?

100

General Questions and Answers / Re: asking for the explanation of the IV curve

« on: October 13, 2017, 12:01 »

Negative differential conductance (NDC), where dI/dV becomes negative, is observed experimentally, and often actively looked for in device simulations. So there are lots of papers on NCD (or NRD, as it's also called). However, in this case it could also be a computational artifact (we did not check if the calculation converged well at the higher bias points). Also, from a more physical point of view, 1 Volt bias applied over a few nanometers is probably above the breakdown voltage anyway, so it might not be a physically realistic scenario.

101

General Questions and Answers / Re: Penta-graphene nanoribbon

« on: October 13, 2017, 11:34 »

Dear Trung Punc,
please attach also the ATK Python script with the structure you have built. Makes it easier to help you...
- Jess

102

General Questions and Answers / Re: Doubt regarding Bandgap

« on: October 13, 2017, 11:32 »

The fundamental band gap (the smallest band gap) is a basic materials property: It is the energy gap between the occupied and unoccupied states below/above the Fermi level in the density of states (DOS). However, the DOS does not indicate which k-points the fundamental transition occurs between (direct or indirect transition). For that, you need to inspect the band structure. However, how do you ensure that the BZ route sampled by the band structure analysis will sample the k-points at which the fundamental transition occurs? In principle, you can never be sure. But, sampling paths between the known high-symmetry points in the BZ usually does it.

So yes, the band gap you "measure" from the band structure of course depends on the BZ route you sample. You may miss the "true" fundamental gap.
I suggest you think hard about exactly how the cited work did the interfacing of different materials, and which unit cells were used, because this decides the BZ symmetries to be sampled in band structure analysis. I also recommend that you get the fundamental band gap in the DOS, to compare to those found using band structure analysis.

103

General Questions and Answers / Re: Is this EDP curve correct?

« on: October 12, 2017, 09:00 »

Perhaps you can also attach the ATK script?

104

General Questions and Answers / Re: Is this EDP curve correct?

« on: October 11, 2017, 08:10 »

DM means DensityMatrix, so if DM=0.0 there are no valence electrons  on that atomic site, which is almost always very bad and indicates poor SCF convergence. You need to inspect the SCF convergence in order to figure out how to fix it. Perhaps it will converge in 20 more iterations? Perhaps electrons are depleted from the central region - electrode boundaries, in which case you perhaps need to use longer electrodes, etc. It's impossible to give a completely general recipe for this kind of thing.

105

General Questions and Answers / Re: armchair mos2 nanoribbon

« on: October 11, 2017, 08:06 »

How will your InSe nanoribbon differ from an ordinary graphene nanoribbon? The Nanoribbon plugin cannot be used?