Messages

1

Scripts, Tutorials and Applications / Re: Script for making data files to plot k-resolved transmission with gnuplot

« on: December 26, 2009, 14:55 »

Dear Anders Blom
If i want to plot the curve in an external program other than Pylab, how to pipe the output to a file such as XYZ?

2

General Questions and Answers / Re: What is the meaning of the two value in the transmission coefficient?

« on: December 8, 2009, 11:37 »

Ok, thank you for your answer

3

General Questions and Answers / Re: What is the meaning of the two value in the transmission coefficient?

« on: December 8, 2009, 11:21 »

then how to find the fermi level in the two probe system? using the "projected hamiltonian energy spectrum" with all the molecule atoms included?

4

General Questions and Answers / Re: What is the meaning of the two value in the transmission coefficient?

« on: December 8, 2009, 10:56 »

In the system, the scattering is an isulator, and the two electrode is different metals, I think the difference of the work functions in the two electrode is the reason of the dipole behavior in the transmission coeficient. But I still don't know how to define the conductantce, form the I/V or from the transmission coefficient/spectrum?

5

General Questions and Answers / What is the meaning of the two value in the transmission coefficient?

« on: December 8, 2009, 10:18 »

when we do the calculation of the transmission coefficient in two probe system, the result will give two value, such as
 Transmission Coefficients: [ 4.43261237e-004  5.75744413e-014]
what is the meaning of them?
sometimes I do the voltage calculations with the same magnitude but different directions, the sign of the current change, and the value of the current is in the same order, but the transmission coefficients will changed with 2 order?
for example, the system with a (0.1 -0.1)Volt, the current is 2.6e-9A, the transmission coefficient is [2.12e-3  3.98e-17]
but the same system with a (-0.1 0.1)Volt, the current is -1.55e-9A, the transmission coefficient is [1.50e-5   1.66e-8]?
from the current value, it seems that the resistant change slightly when the bias is opposite, but from the transmission coefficient, it change dramatically, which one shoud we based to calculate the conductance of the two probe system?

6

Future Releases / Re: What is your Linux distribution?

« on: December 8, 2009, 09:59 »

I use the Rocks and the Redhat

7

Scripts, Tutorials and Applications / Re: Script for calculating the effective mass in semi-conductors.

« on: March 26, 2009, 03:48 »

Hi Nordland
I have tested your script with the BaTiO3, this model have 5 atoms.
the calculated bandstruture is attatched below.
for the cubic phase, both the conductiviey and DOS electron effectivemass gave 4.57579367772 me, but the experimental value for this phase is about 0.5 me.
and for the tetragonal phase, the
# ---> Conductivity          = 0.487857138832 me
# ---> Density of states     = 0.805148177393 me
I have two question:
firstly, from the bandstructure, the curvature at the CBM in G (0. 0. .0.) is almost the same, why the electron effectivemass have so large difference.
secondly, in the script, the experssion for the DOS effectivemass is

Code

print '# ---> Density of states     = %10s'%((MH)**(2.0/3.0) * (abs(ml._value()*mt1._value()*mt2._value()))**(1.0/3.0) * me)

,
 but according to the paper you give us Paper with a note on conductivity effective mass.http://mems.caltech.edu/courses/EE40%20Web%20Files/Supplements/01_Effective_Mass.pdf, it should be

Code

 Density of states     = %10s'%((MH)**(3.0/2.0) * (abs(ml._value()*mt1._value()*mt2._value()))**(1.0/3.0) * me)

,
it will affect the result of Si, but has no influence on the BaTiO3 here.

8

Scripts, Tutorials and Applications / Re: Script for calculating the effective mass in semi-conductors.

« on: March 18, 2009, 08:58 »

in the effective mass calculation,
what is the physical meaning of the Conductivity  effectivemass and the Density of states   effectivemass?

Code

print '# Electron effective mass' 
print '# ---> E                     = %10s'%(b[step])
print '# ---> Conductivity          = %10s'%(3.0 * (abs((1/ml._value()) + 1/mt1._value() + 1/mt2._value()))**(-1) * me)
print '# ---> Density of states     = %10s'%((MC)**(2.0/3.0) * (ml._value()*mt1._value()*mt2._value())**(1.0/3.0) * me)

in wikipedia, the effectivemass is given for one definition.
http://en.wikipedia.org/wiki/Effective_mass_(solid-state_physics)
besides that, I have do a calculation of the Si with (15, 15, 15) mesh, the band structure (see attach) didn't have 6 lowest point of the conducting band in the brillouin zone?

9

Scripts, Tutorials and Applications / Re: Script for calculating the effective mass in semi-conductors.

« on: March 15, 2009, 05:18 »

Thank Nordland, I will try to do it in SiO2

10

Scripts, Tutorials and Applications / Re: Script for calculating the effective mass in semi-conductors.

« on: March 12, 2009, 15:11 »

Is there any Progress?

11

Scripts, Tutorials and Applications / Re: Script for calculating the effective mass in semi-conductors.

« on: March 6, 2009, 14:31 »

if you can wait a couple of hours I will try to generalize it to handle indirect semi-conductors correctly.

 

12

Scripts, Tutorials and Applications / Re: Script for calculating the effective mass in semi-conductors.

« on: March 6, 2009, 04:45 »

Thank you Nordland, but the script seems can only calculated the effectivemass in the G point, if there is an indirect bandgap material, it is improper to use this script, I have revised some of the code in this script to do calculate the effectivemass in an indirect bandgap material, but the result is no so satisfied:
Direct Band Gap =  6.97405383307 eV
Indirect Band Gap = 6.69934035399 eV
----------------------------------------------------------------------
# Electron effective mass    = 0.0219170891857 me
----------------------------------------------------------------------
# Hole effective mass (1)    = 0.069356447541 me
# Hole effective mass (2)    = 0.0345840434497 me
# Hole effective mass (3)    = -2.93394832023 me
----------------------------------------------------------------------
# Average hole effectiv mass = -0.943335943081 me
----------------------------------------------------------------------

(the experimental value of electron effectivemass for alpha SiO2 is 0.5me, and the effective hole mass is 0.38m)

 is there anything wrong with my revised script?

13

Scripts, Tutorials and Applications / Re: How to apply a force on the bulk system

« on: February 19, 2009, 15:27 »

Hi, Nordland
Thank you for the script, but i still have a question in the last two line of the GaN.py

Code

bands = calculateEnergyBands(scf,[(0.0,0.0,0.0)])
print '# Strain = %s Band gap = %s'%(ezz, bands.band(8)[0] - bands.band(7)[0])

how do you know that the gap is between bands.band( 8 )[0] - bands.band(7)[0], should we do some bandstruture before to define the position of the VBM (bands.band(7)[0]) and CBM (bands.band( 8 )[0])?

Moderator edit: placed code in (code) to avoid sunglasses (bb code eight) 8 )

14

Scripts, Tutorials and Applications / Re: How to apply a force on the bulk system

« on: February 18, 2009, 04:10 »

Hey Rosen.

I found this script that I have made some time ago. It is a module for creating a strain on bulk configuration
in order to model the behavior of the bandgap under strain for GaN.

I have uploaded the functionality here, and the results I got from my studies on GaN.

Perhaps you can use it for you work as well.

is it possible to post the script of the GaN example under strain.?

15

General Questions and Answers / Re: Is it possible to use the ATK to calculate the ferroelectric polarization?

« on: January 8, 2009, 14:16 »

Is it the code complicated, can you put the script on the "Scripts, Tutorials and Applications" section?