Messages

16

General Questions and Answers / Re: Calculate fermi velocity

« on: February 16, 2012, 13:19 »

fermi velocity is given by vf =      dE/dK
                                        -----------
                                               (h*)
h* is reduced planck constant

since unit of h* is (eV)(second)
and velocity in (m)/(Sec)

dE/dK should be  (eV)(m)

so in the script the unit of 'eps' (k points) is in meters^-1 OR angstrom^-1 OR nanometer^-1 I need ur help here.

looking at the values people have got fermi velocity of 10⁶ m/sec. in graphene

17

General Questions and Answers / Re: Calculate fermi velocity

« on: February 16, 2012, 12:22 »

i was having trouble with imports so.... i copied the code below the BandstructureK.py file and removed the import statement its working now.

18

General Questions and Answers / Re: Calculate fermi velocity

« on: February 16, 2012, 12:05 »

Hi Thanks for the help . I am still trying to find where should i copy BandstructureK.py class file?? so that i won't get the import-errors??

Traceback (most recent call last):
  File "c:\docume~1\ibm\locals~1\temp\5896631062587926.py", line 4, in <module>
    from BandstructureK import Bandstructure 
ImportError: No module named BandstructureK

I copied this in default directory (where analysis.nc gets saved automatically) but still i am getting error.
or do i need to keep the class file inside atkpython folder???

19

General Questions and Answers / Calculate fermi velocity

« on: February 14, 2012, 10:44 »

Graphene ,silicene and germanene show linear dispersion at the K point in band dig.How can i get the slope dE/dk from bandstructure???  ???Is it possible to use some kind of nanolanguage script to calculate fermi velocity of electrons by taking slope of E-K graph.Please help.

20

General Questions and Answers / Re: Warning msg : Graphene junction

« on: February 10, 2012, 12:29 »

ok, these residuals are very small in magnitude  and close to the required ones...so all is ok.

21

General Questions and Answers / Warning msg : Graphene junction

« on: February 10, 2012, 11:15 »

I was running some transmission spectra calculations for Graphene junction device. I used multi grid solver keeping Neumann boundary condition for electrodes and Dirichlet for central regions .K points were kept as 1X1X51 using extended huckel device calculator.The calculation is running fine but i am getting warning messages in the log as shown below.What i should do to correct this?

################################################################################
# WARNING                                                                 
#                                                                             
# The computed multigrid residual is greater than the required accuracy.     
#                                                                             
# Computed residual :   1.29180e-010                                           
# Required accuracy :   1.00000e-012 

22

General Questions and Answers / Re: Phonon dispersion curves

« on: February 10, 2012, 06:47 »

hi thanks this is useful... .as of now is there an indirect manual way through which i can try my hands on phonopy/fropho??. I have installed python on my sytem separately.Also, all files are linux/unix based i find no windows installer files for phonopy.

23

General Questions and Answers / Phonon dispersion curves

« on: February 9, 2012, 06:10 »

In atk 11.8.2 is there a way to draw phonon dispersion curves (for nanoribbon or some other configuration) to check stability??

24

General Questions and Answers / Re: Silicene nanoribbon configuration

« on: January 25, 2012, 09:31 »

thanks for clarification.

25

General Questions and Answers / Re: Silicene nanoribbon configuration

« on: January 24, 2012, 09:32 »

Hi,

Can someone please answer me about the distance between metallic plates so that i can know the value of electric fields.

26

General Questions and Answers / Re: Silicene nanoribbon configuration

« on: January 20, 2012, 09:10 »

I was trying to calculate the band gap variation with electric field of silicene armchair ribbon with gates.
Here are the two metallic regions defined in the script:

metallic_region_0 = BoxRegion(
      0*Volt,
      xmin = 8*Angstrom, xmax = 23*Angstrom,
      ymin = 4*Angstrom, ymax = 4.5*Angstrom,
      zmin = 0*Angstrom, zmax = 26.2*Angstrom
   )

metallic_region_1 = BoxRegion(
      0*Volt,
      xmin = 8*Angstrom, xmax = 23*Angstrom,
      ymin = 21.5*Angstrom, ymax = 22*Angstrom,
      zmin = 0*Angstrom, zmax = 26.2*Angstrom
   )

After giving the gate voltage the perpendicular electric field is defined as the ratio of:
 
             (Gate voltage)
     -- -----------------------------
(distance between two metallic plates)

Looking at the dimensions of metallic region in code what value should i choose for denominator??

is it (ymax_of_1 - ymin_of_0)=(22-4)=18A
or
is it (ymin_of_1 - ymax_of_0)=(21.5-4.5)=17A

27

General Questions and Answers / Re: Silicene nanoribbon configuration

« on: January 20, 2012, 09:01 »

Hi, Thanks i have done the energy analysis of 'no spin','anti' and 'parallel' spins
yes, the energy difference is there although very small.
I have given spin to the edges i.e, one edge  has parallel spin while the other has opposite spin.
Thanks for the help.

28

General Questions and Answers / Re: Silicene nanoribbon configuration

« on: January 19, 2012, 09:42 »

Hi I have gone through this and replicated the same for silicene zigzag nanoribbons but i want to calculate 'TotalEnergy' for both spin polarised (Antispin case) and without spin and calculate the energy difference that exists in two cases as i vary the width of ribbon . but my problem is i am getting same total energy for both schemes??

29

General Questions and Answers / Re: Silicene nanoribbon configuration

« on: January 18, 2012, 13:36 »

In some of the technical papers it is written that graphene nano ribbons with spin polarized edges have much lower energy than non-spin polarized.Also anti ferromagnetic spins have lower energy than parallel spins.But in ATK-VNL whenever we give initial spin the optimization routine goes to preferred intrinsic spins of atoms and the total energy of the ribbon always comes out same (with or without spin) 

Is there a way through which i can find the energy difference between non-spin and spin polarization of edge states of ribbon???

Thanks in advance!

30

General Questions and Answers / Re: Silicene nanoribbon configuration

« on: January 17, 2012, 11:18 »

Hey Nordland!...thanks for this useful info