Messages

1

General Questions and Answers / Re: lddos calculation using GGA

« on: May 23, 2013, 20:48 »

Thank you so much Anders..I got it and I will try to build the device that way. However should I use some specific calculator like GGA or MGA, LCAO or huckel for the device simulation?

2

General Questions and Answers / lddos calculation using GGA

« on: May 16, 2013, 20:48 »

Hi,

I am currently working on the calculation of a 2D MoS2 device. As Ander's recommendation, in my script I first do a geometry optimization before calculating the lddos. And I tried to use GGA for the calculation. The program aborted and I checked the log and I see a non convergence in the simulation and the error message is shown below. I suspect that is because I am using quasi newton for the optimization and I am wondering how I should change the restricts. I am also thinking that for a device simulation if it is proper to use 11 k-point sampling and 60 Hartree as pseudo potential since that will be very time-consuming. The settings worked pretty well for the lattice simulation with just the basis of A moly atom and a sulfur atom but it is not working for the device. Can I know what can I do to modify the script to have the simulation well set? Thank you.
 File "/home/koesters/suxxx172/suxxx172//ATKSIMS/shellscripts/20130505_lddos.py", line 488, in <module>
    optimizer_method=QuasiNewton(),
  File "./zipdir/NL/Dynamics/Optimization/OptimizeGeometry.py", line 229, in OptimizeGeometry
  File "./zipdir/NL/Dynamics/Optimization/OptimizeGeometry.py", line 338, in runSimultaneousRelaxation
  File "./zipdir/NL/Dynamics/Optimization/OptimizeGeometry.py", line 263, in runRelaxation
  File "./zipdir/NL/Dynamics/ASEAtomsInterface.py", line 173, in get_forces
  File "./zipdir/NL/Dynamics/ASEAtomsInterface.py", line 97, in _update
  File "./zipdir/NL/Calculators/LCAOCalculator/Analysis/FastEnergyForcesStress.py", line 28, in energyFunction
  File "./zipdir/NL/Calculators/LCAOCalculator/Analysis/FastEnergyForcesStress.py", line 65, in _checkAndUpdate
  File "./zipdir/NL/Calculators/LCAOCalculator/Analysis/FastEnergyForcesStress.py", line 90, in _update
  File "./zipdir/NL/Calculators/LCAOCalculator/Analysis/EnergyForcesStress.py", line 72, in calculateLCAOEnergyForcesStress
  File "./zipdir/NL/Calculators/LCAOCalculator/Analysis/EnergyForcesStressUtilities.py", line 19, in setupLCAOEnergyForcesStressCalculator
  File "./zipdir/NL/Calculators/LCAOCalculator/Analysis/EnergyForcesStressUtilities.py", line 344, in setupBackengineConstraints
NL.ComputerScienceUtilities.Exceptions.NLValueError: Stress can only be calculated in the z-direction for devices.
 

3

General Questions and Answers / k-points and periodic boundary conditions

« on: January 8, 2013, 20:05 »

Hi.. I did a new simulation with trying to calculate a periodic ribbon, and I am still using periodic boundary conditions in the y direction. But it never finished. Is there some problem with the periodic boundary conditions I was using? I got the py file attached. Thank you very much.

4

General Questions and Answers / Re: gate scan can not be finished

« on: December 17, 2012, 20:25 »

Thank you. So if the lddos calculation is just for analyzing the current flow in a device, what calculation I should do to plot the band information along the device like in other simulation tools? I think the band diagram is important to device guys like me for the information like band alignment..

5

General Questions and Answers / Re: gate scan can not be finished

« on: December 14, 2012, 00:28 »

Thank you.. So where should I save the device configuration after each scan point? Should I put that right before the saving of transmission spectrum at each point?
I also got a question that do I need to load the updated device configuration at the beginning of every step or just like right now. I am thinking if I load the original configuration at each step, the saving would not help right?
One more problem is that I calculated the energy dependent lddos at equilibrium and plotted lddos vs z and energy using the script just as in the tutorial. I got the figure attached and it is just from this device configuration. In the tutorial the lddos was calculated by adding all the dos at every location of z axis. It comes up that the figure make no sense for analysis. I can not extract information from that. Can I have some band diagram thing like what we usually do in the device analysis? Or how does this lddos figure can tell the information of the band structure information of the device? Thank you.

6

General Questions and Answers / Re: gate scan can not be finished

« on: December 7, 2012, 02:03 »

And by the way, when I try to visualize the results like transmission spectrum and device density of states in the vnl window when I clicked the show button, nothing popped out even a blank window...I am wondering what is going on.

7

General Questions and Answers / gate scan can not be finished

« on: December 7, 2012, 01:26 »

Hello, I am running a gate scan of a MOSFET to plot the Id vs Vg curve of it. First I calculated the device configuration and transmission spectrum at equilibrium. And then I use the analysis from file to do a gate scan from -2V to 2V. the equilibrium transmission spectrum take like 5 hours to finish, but the gate scan has been running for 24 hours and just complete 2 points. Can you take a look at my script and help me to figure it out? Thank you very much.

8

General Questions and Answers / Re: k-points and periodic boundary conditions

« on: December 4, 2012, 03:56 »

I think I got it..Thank you very much

9

General Questions and Answers / Re: k-points and periodic boundary conditions

« on: December 4, 2012, 00:53 »

Sorry but I mean how can I "mark" in the script that a direction is infinite?

10

General Questions and Answers / Re: k-points and periodic boundary conditions

« on: December 3, 2012, 20:47 »

So how can I tell if a direction is finite or infinite? By boundary conditions or the vacuum added? Thank you

11

General Questions and Answers / Re: k-points and periodic boundary conditions

« on: December 2, 2012, 03:07 »

Ok, but in my previous simulation where I did not use a neumann boundary condition in the direction I have gates, the simulation did not converge. However, after the neumann boundary conditions added and multigrid solver used it converged better. So can I say that if I have gates in some direction it is better to use neumann and multigrid and if there are no spatial regions I can simply add vacuum at the edge of the cell and use single k-point? Thank you

12

General Questions and Answers / Re: k-points and periodic boundary conditions

« on: November 30, 2012, 02:25 »

Thank you but I have searched through this forum and that I got this answer to some post
"In X and Y, you can basically have two situations: the structure can be finite (like a nanotube, or a ribbon). Since the model is anyway periodic, you add some vacuum so the periodic copies don't interact. In this case, 1x1x100 would be the appropriate k-point sampling.

If you have periodicity in X and Y, like if the electrodes are formed by a cleaved crystal surface. Then you need NAxNBx100 k-points, and how many NB and NB depends on the length of the period - the shorter the period length, the more k-points. So 1 might be still ok if the period is really long, which usually means you make several repetition of the system.

You can also have a mixture in X and Y, like finite in X and periodic in Y. This would be the same of a graphene sheet in the YZ plane. Then 1xNBx100 would be an appropriate sampling, with the same rules applying for NB as just above.

So in short: for a graphene sheet - 1x9x100 (or 12, or 15, etc). For a ribbon, 1x1x100."

Does that mean if I have periodicity and infinity in some direction I need to use multiple k-points in that direction and if it is finite in some direction I can just use 1 k-point in that direction?
And do I need to use neumann boundary conditions in the finite direction? Thank you

13

General Questions and Answers / k-points and periodic boundary conditions

« on: November 29, 2012, 07:42 »

I am kind of confused...The boundary conditions are set by determining the k points sampling right? What does the k-point sampling mean in both electrode and transmission spectrum part? My understanding is that if I set the k-point sampling to be 1 in a direction, in that direction the calculation will be infinite...

14

General Questions and Answers / Re: a single localDeviceDOS simulation took forever to run

« on: November 2, 2012, 02:12 »

Thank you..I just checked the log file of this simulation and it says the residue is in order of 1e14 and the tolerance is 1e-12..It seems it did not converge...What can I do to make the simulation converge better? Thank you very much.

15

General Questions and Answers / Re: a single localDeviceDOS simulation took forever to run

« on: October 28, 2012, 22:50 »

Thank you very much for your help and I finally had the job finished and got the nc file. Now I would like have a band diagram analysis of the device. How can I plot the band diagram(like band energy along z axis) using VNL from the nc file? I already did the DeviceLDOS calculation in the former script..Thank you very much.