Messages

1

General Questions and Answers / Why Molecular Orbital is visualised same in VNL for different options ?

« on: August 12, 2010, 19:07 »

Hello,

I plot HOMO and LUMO levels within VNL. Different options of VNL such as sign, magnitude and value yield same isosurface (only the color format is changed). Why are they same, what is the definition ? What do we visualize in vnl ?

2

General Questions and Answers / How to Calculate Vacuum Level ?

« on: June 20, 2010, 16:21 »

How the vacuum level can be calculated by using ATK ?  Is there any command or script for this job ?

3

General Questions and Answers / Does the Theory Objects non-Metallic Electrodes ?

« on: December 30, 2009, 17:41 »

Do we have to use metallic electrodes during ATK calculations? Does the theory used by ATK have objection to semiconducting electrodes ? Thanks to shifts in levels due to changing bias, can't we calculate any current throught the molecular device at some voltage values.

4

General Questions and Answers / Re: Reading Spin Dependent Transmission Data from nc file

« on: December 13, 2009, 22:48 »

Thank You

5

General Questions and Answers / Reading Spin Dependent Transmission Data from nc file

« on: December 13, 2009, 15:00 »

Hello, I use the script given in ATK tutorial but it works only for unpolarized systems. How I must modify it to get up and down spin transmissions.

The script is :

from ATK.TwoProbe import *
from ATK.MPI import processIsMaster

old_scf_zero_bias = \
    restoreSelfConsistentCalculation("bare.nc")

temporary_list = range(-50,50,1)
energy_list = []
for i in temporary_list:
    energy_list.append(i/10.0)

trans_spectrum = calculateTransmissionSpectrum(
       old_scf_zero_bias,
       energies = energy_list*electronVolt
       )

trans_energy = trans_spectrum.energies()
trans_coeff = trans_spectrum.coefficients()
trans_energy = trans_energy.tolist()
trans_energy.reverse()
trans_coeff = trans_coeff.tolist()
trans_coeff.reverse()

while len(trans_energy)>0:
    if processIsMaster(): print trans_energy.pop(),'\t',trans_coeff.pop()

6

General Questions and Answers / Re: How to recalculate data from nc file with float

« on: December 1, 2009, 14:32 »

It is ok now... following script works


from ATK.MPI import processIsMaster

import numpy


for i in numpy.arange(0.00, 1.01, 0.01):
   
    energy=calculateTotalEnergy(restoreSelfConsistentCalculation("21-%.2f.nc" % i)).inUnitsOf(eV)   
    if processIsMaster(): print 'TOTALENERGY', i, energy

7

General Questions and Answers / Re: How to recalculate data from nc file with float

« on: December 1, 2009, 13:43 »

BAD NEWS...

scf = restoreSelfConsistentCalculation("a%g.nc" % i)
NLValueError: Invalid NetCDFFile.
Traceback (most recent call last):
  File "<string>", line 12, in ?
NLValueError: Invalid NetCDFFile.

8

General Questions and Answers / Re: How to recalculate data from nc file with float

« on: December 1, 2009, 13:11 »

Thank you for your time Anders...

9

General Questions and Answers / How to recalculate data from nc file with float

« on: December 1, 2009, 12:30 »

Hello,

I want to read datas from nc files named as ,for example,  a1.5.nc, a1.6.nc, a1.7.nc, a1.8.nc, a1.9.nc,

How can I restore these scf calcualtions for reading datas with float command.

10

General Questions and Answers / How to get net electron density ?

« on: September 29, 2009, 15:17 »

How can I get net electron density (Charge^UP-Charge^DOWN) and store it as a VNL file ?

11

General Questions and Answers / Re: Can anyone tell me the reasons?

« on: May 20, 2009, 14:23 »

ATK uses the charge density of previous calculation. If you choose smaller voltage steps such as 0.01 volt, better convergence may be provided.

12

General Questions and Answers / Re: Smearing the I-V curve

« on: April 30, 2009, 15:59 »

After a lot of test calculations (and your useful advices), I am happy to announce that

Number of points is the most effective paramater to get reasonable I-V curves

Additionally, Electron temperature must be taken in the range of room temperature.

13

General Questions and Answers / Re: Smearing the I-V curve

« on: April 27, 2009, 13:53 »

If the transmission spectrum is zero then the current will be zero

But I guess T(E) is not exactly zero, just very small. In that case, I guess the current integration can have a large effect on the results. Can you post an example of the transmission spectrum, at two different biases? Perhaps in log-scale.

If transmission coefficient is zero at a certain energy value it has no contribution to the current (here we are agree) but current does not have to be zero (it may has a finite value due to previous transmission contributions ).
I attached transmission spectrum for up and down at zero bias ( for finite bias, negligible changes occur and we have almost same transmissison spectra)

I am sorry, I have no log-scale transmission.

As you see, there is only one peak (around fermi level) for up and down transmission, and I-V curves (see previos message) need to be corrected...

14

General Questions and Answers / Re: Smearing the I-V curve

« on: April 27, 2009, 11:43 »

black and red curves correspond to UP and DOWN spin current.  I said that they are strange because there are peaks and dips in I-V curve while corresponding transmission spectra has zero transmission coefficients.

15

General Questions and Answers / Re: Smearing the I-V curve

« on: April 27, 2009, 11:15 »

bad news...  I have been tried various parameter sets as follows.

green_function_INFINITESIMAL === e-5, e-9
TEMPERATURE  === 600, 300 and 5 Kelvin
TOLERANCE      === e-5 and e-8

My I-V calculation still has strange peaks (as can be seen in attached figures)
What are the  paramaters directly affect I-V values.