Topics

16

General Questions and Answers / some theory backgroud of photocurrent about the indirect gap semiconductor

« on: February 9, 2019, 05:02 »

Dear:
i have a question about the photocurrent model in quantumATK.
If there is an indirect gap semiconductor, its direct gap is A, and indirect gap B , of course, A is bigger than B, so it is an indirect band gap .
so i am wondering in the theoretical framework of quantumATK, the allowed smallest transition energy of an electron from valence to conductance is A or B? i.e the indirect inter-band transition is allowed? because it needs phonon energy because momentum difference .


 

17

General Questions and Answers / is the photocurrent would be applied to two-probe coniguration

« on: February 8, 2019, 11:07 »

HI:
I am looking for the help file about the photocurrent calculation, but there are only for PN-junction, not two-probe configuration,
so I am wondering the photocurrent can be applied to a two-probe configuration?
please give me some hints and help.
thanks very much

18

General Questions and Answers / how to calculate the band gap of graphene/mos2 heterostructure correctly

« on: January 22, 2019, 11:45 »

Hi:
i want to get the correct band gap of graphene/mos2 heterostructure,
one method is to use MGGA, but as the manual said, the c-parameter should test manual because the supercell have big vacuum region, because there are no corresponding bulk graphene/mos2, so the c-parameter can not be determined by known value as the manual said,
so i am wondering how to test the MGGA-c-parameter.
and another question is is there any better to calculate the band gap of such two-dimensional heterostructure in ATK?

THANK YOU VERY MUCH

19

General Questions and Answers / how to analysis the quantum interference based on the transmission pathways

« on: January 15, 2019, 07:39 »

Dear all:
I have modeled a molecular electron device, and I want to know is there any interesting quantum interference between molecular and electrode.
as I know the transmission pathways can help it.
but transmission pathways can only get the direction of current flow between atoms? how the interference can be analyzed   

anyone can help me
great appreciated

thank you

20

General Questions and Answers / is the hartree_difference_potential flat?

« on: December 7, 2018, 13:23 »

Hi ATK support:
I tried to plot the Hartree difference potential to check the central region is enough long or not,
the plot is in the attachment.
but I do not know it is flat or not?, because I set the Y axis is from -1 to 1 eV. when I set Y -0.06 to  0.12 eV , it seems not flat.
so my question is how to set Y axis region when I check the length of  central region.
 

21

General Questions and Answers / NEGF not Convergence：the electron distribution is wrong how to plot deltaH

« on: December 5, 2018, 05:25 »

Hi all:
I face an issue about device convergence, and according to the NEGF Convergence Guide, I first need to check the central region is long enough or not. But my understanding is because the electron distribution is wrong for not convergence,   
so the resulting plot deta_Ha is also wrong,
and then how could I know the convergence issue is due to the length of the central region.

thanks very much if someone can help me.

cheers

22

General Questions and Answers / about the initial spin of system containing Hydrogen atoms

« on: November 27, 2018, 07:33 »

Hi all:

a few days ago, I found a page titled "potential problem xxx", about initial spin setting up. I remember it said it is better to set initial spin 0.99 not 1 to avoid the convergence  problem,
but I cannot remember where to find the page online.
is there anyone kindly to let me know where it is now

3x very much!

23

General Questions and Answers / the fixed-spin can only for the spin direction not spin magnitude?

« on: October 24, 2018, 14:33 »

Hi all：
i want to fix the magnitude of spin for some atoms in molecular, is there possible now?


thanks very much?

24

General Questions and Answers / the bader charge analysis can be used to device configuration?

« on: October 24, 2018, 14:27 »

hello all:
I receive a reviewer comments, he required me that the Milliken analysis would be accurate to my device configuration , and ask me to do bader analysis,

so i am wondering how to calculation bader charge because i look up it is only for bulk configuration , not the device configuration.
now my version 2018.06

thanks very much

25

General Questions and Answers / is it possible to reproduce a very very tiny bandgap~2mev

« on: May 3, 2018, 03:52 »

Hi Sir:
i want to reproduce the bandgap ~2meV, which is calculated by PAW pp with VASP,
so i am wondering is it possible to reproduce it,  because at present, i used DZP, and try as many as possible K points,  in on direction i used 101 K along high symmetry line, it seems not work, i think maybe LCAO have not such precision ?
please give me a hint.

thanks very much .

 
 

26

General Questions and Answers / the iteration control, the mixing variable and and algorith can not be changed

« on: May 3, 2018, 03:43 »

Dear Sir;
 in my VNL gui, (2017.12 VERSION ,)the new calculator--->iteration control>>>> mixing variable and and algorith can not show the drop down option.please see the figure. others option seems OK

please check it

thanks very much.

my system is linux, Linux version 2.6.32-220.el6.x86_64 (mockbuild@x86-004.build.bos.redhat.com) (gcc version 4.4.5 20110214 (Red Hat 4.4.5-6) (GCC)

27

General Questions and Answers / how to specify the K point not along the high symmetrical direction

« on: April 30, 2018, 07:04 »

Hi
I am doing a band structure calculation, and I want to know one K point that  is not along the high symmetrical direction.
so I am wondering how to specify the Fraction position in BZ, because in the option where can not input K,M,G,V ..
I need your help

thank you very much

28

General Questions and Answers / why the electron difference density is not consistant with previous study

« on: April 25, 2018, 11:28 »

Dear All:

i consists a MoS2-graphene hetero structures using the Interface tool in the Builder option.The parameters chosen are shown in figure 1. the relaxed geometry is a=6.321,b=6.321,c=24.804. the distance between Gr and Mos2 is 3.34 angstrom.
the relaxed configuration  py file are attached.
and we noticed that in our configurations, one C atoms of Gr is located uopn the S atom in mos2. so we though it is very close to TS configuration presents in the Nanoscale, 2011, 3, 3883–3887.

but we plot the electron difference density, and found it is NOT consistent with that in eNanoscale, 2011, 3, 3883–3887. the different details are show in figure 2 and figure 3

so i am wondering what is the reason make the electron difference density different, especially the C layer lost electrons while in our calculation C  get electrons.
 
i need your help.

 
thanks a lot

29

General Questions and Answers / how to acesss "how to simulate interfaces in electronics at the atomic scale"

« on: April 7, 2018, 13:41 »

Dear Sir:

i am interesting the webinar,"how to simulate interfaces in electronics at the atomic scale",  but i missed the time, so i am woundering is there any recordings to access?

thank you very much

30

General Questions and Answers / how to convert the interface cell into orthorhombic cell for electrode usage

« on: February 2, 2018, 06:55 »

Hi :

I have built an interface, and the cell is chosen as unit cell (see figure1)with
a=14.704
b=5.47397
c=11.395
alfa=43.8979degree
beta=90 degree
gama=90 degree
because the cell is most stainless, about 4.1%.
as it knows, if I build the interface as an electrode, the cell should be an orthorhombic cell. I used the ''supercell'' option and choose based (body or face) orthorhombic.but it cannot be made to the orthorhombic cell at all. the option ''device from bulk"
so I am wondering how I can make it as an electrode.