Messages

46

General Questions and Answers / How to plot electrostatic potential?

« on: February 22, 2013, 14:30 »

Dear QuantumWise staff:

how to plot electrostatic potential (not electrostatic difference potential) using ATK2011.8?

47

General Questions and Answers / Re: Questions on sequential tunneling

« on: December 31, 2012, 02:06 »

Thank you professor Anders and happy new year

48

General Questions and Answers / Re: Questions on sequential tunneling

« on: December 30, 2012, 04:09 »

Thank you  professor kstokbro
another question, what's the different between incoherent tunneling and  inelastic tunneling? the same?

Regards

49

General Questions and Answers / Questions on sequential tunneling

« on: December 28, 2012, 04:02 »

Dear QuantumWise staff:
     
      A few days ago, i was fortunate to read the paper by professor Anders and Kurt (IEEE,2011), it is very helpful. Sequential tunneling mentioned in the paper puzzle me a lot. 

i don't know what' the different between Sequential tunneling, incoherent tunneling, hopping, and Coulomb blockade regime?

in my view:
Ⅰ. ①(the length of central molecule is smaller than 2.5nm). if the molecule-electrode coupling is strong, the transport regime is coherent tunneling, the incident wave function tunnel through the electrostatic potential field  does not cause any change of the electrostatic potential field. it is to say that the incident electron need only one step from left electrode to right electrode. if the bias is low, there is no "molecule energy" in the bias window the tunneling is weak, if the bias is high, some molecule eneries in the bias window, the tunneling is orbital-mediated and it is strong. DFT-NEGF(ATK) can deal with it very powerful.
Am i right?

②(the length of central molecule is longer than 2.5nm). the incident electron will stay for a long time in a potential well of the central molecule, the phase of incident electron is changed due to the interaction. at this time, incoherent tunneling is the main transport regime, and it can be decompose into a series of coherent tunneling. is it means Sequential tunneling?  i only know hopping is temperature-dependent, tunneling is not, and hopping is over the barrier, tunneling is through the barrier.what' the different between Hopping and sequential tunneling?
 

Ⅱ. if the molecule-electrode coupling is weak, couloumb blockade effect between the molecule and electrode is established, the electron spend long enough time stay in the central region, so, electron(incident)-electron(molecule) exchange-correlation interaction and interaction between incident electron wave and molecule vibration can't be neglected. the interaction lead to Kondo effect(at Kondo temperture) and inelastic tunneling. DFT-NEGF(ATK) can not simulate.  Am i right?


Regards
kaypu





     

50

General Questions and Answers / Re: Question on script of energy dependent LDOS

« on: December 27, 2012, 04:03 »

thank you professor Anders  i will try

it terminated
*************************************************************************
This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.
********************************************************************************

what's wrong with it?  is it not enough memory?  i use 12.2

51

General Questions and Answers / Re: Question on script of energy dependent LDOS

« on: December 27, 2012, 01:27 »

thank you professor Anders

i have four separated LDOS.nc with different energy interval. Using the script, i can only plot the picture from one of the LDOS.nc(maybe the energy interval is -1eV~-0.5eV), how to modify the script to plot the four LDOS.nc into one picture?

52

General Questions and Answers / Question on script of energy dependent LDOS

« on: December 26, 2012, 02:02 »

Dear QuantumWise staff:
   
      i've got a problem in calculating energy dependent LDOS using the script in "http://www.quantumwise.com/documents/tutorials/latest/MolecularDevice/index.html/chap.analysis.html#sect1.analysis.lddos", maybe the memory of my laptop is not enough. So i save the LDOS in separated NC(-1~-0.5eV: LDOS0.nc; -0.4~0eV: LDOS1.nc; 0.1~0.5eV: LDOS2.nc; 0.6~1eV: LDOS3.nc).
     
      how to plot all of these NC in one pic?

PS: the script in the website:

      # import list with lddos
lddos_list = nlread('lddos.nc', LocalDeviceDensityOfStates)            .............how to read all of the NC using nlread?

#Find the z-spacing
dX, dY, dZ = lddos_list[0].volumeElement().convertTo(Ang)
dz = dZ.norm()
shape = lddos_list[0].shape()
z = dz * numpy.arange(shape[2])

# calculate average lddos along z for each spectrum
energies = []
lddos_z = []
for lddos in lddos_list:
    energies = energies + [lddos.energy().inUnitsOf(eV)]
    avg_z = numpy.apply_over_axes(numpy.mean,lddos[:,:,:],[0,1]).flatten()
    lddos_z = lddos_z + [avg_z]

# plot as contour plot
# make variables
energies = numpy.array(energies)
X, Y = numpy.meshgrid(z, energies)
Z = numpy.array(lddos_z).reshape(numpy.shape(X))


import pylab
#plot the LDDOS(E, z)
pylab.xlabel('z (Angstrom)',fontsize=12,family='sans-serif')
pylab.ylabel('Energy (eV)',fontsize=12,family='sans-serif')
contour_values = numpy.linspace(0,0.02,21)
pylab.contourf(X, Y, Z, contour_values)
pylab.colorbar()
pylab.axis([6,16,-3, 3])

pylab.title('Au-DTB-Au : LDDOS(E, z)')
pylab.savefig('lddos.png',dpi=100)


pylab.show()   


Regards
kaypu

53

General Questions and Answers / Re: Question on combining nc

« on: December 26, 2012, 00:52 »

Thank you professor Nordland

54

General Questions and Answers / Question on combining nc

« on: December 25, 2012, 02:22 »

Dear QuantumWise staff:

     i want to combine four separate NC into one NC, how to do it?

Merry Christmas

55

General Questions and Answers / Question on Van der Waals potential in DFT-NEGF

« on: December 14, 2012, 10:14 »

Dear QuantumWise staff:

       i want to study the transport properties fo Li absorption in a few layer graphene, and Van der Waals interaction is important in multilayer graphene, it will change interlayer spacing of the multilayer graphene. using DFT-D, i can opt the system, for transport of DFT-NEGF, can ATK suit for the job? or modify the E_XC, maybe +empirical potential.

Regards

56

General Questions and Answers / Re: Question on initial state under bias

« on: December 14, 2012, 07:36 »

thank you professor Anders

57

General Questions and Answers / Question on initial state under bias

« on: December 14, 2012, 03:20 »

Dear QuantumWise staff:
     
     i  use initial state of low bias to calculate the state of high bias.  if the initial state of low state i used is an unconverged state(bias= 1.5V, dH=1E-1), fortunately, i got converged state(bias=1.6, dH=1E-5). is it safe to use this converged state to get TE or DOS under 1.6V?

Regards

58

General Questions and Answers / Re: Question about electrostatic difference potential

« on: December 3, 2012, 01:13 »

thank you professor kstokbro

59

General Questions and Answers / Question about electrostatic difference potential

« on: December 2, 2012, 01:51 »

Dear QuamWise staff:

   professor Anders  told the electrostatic difference potential is the solution to the Poisson equation where on the right-hand side you have the electron difference density, which is the (total) electron density minus the density of the neutral atoms on this forum.

i don't know how to define density of the neutral atom? is it the summation of the Isolated atom?

another question, atk use electrostatic difference potential to calculate voltage drop,  it is to say that : Voltage drop= electrostatic difference potential(under bias)- electrostatic difference potential(zero bias), we can also get the voltage drop using electrostatic potential.  it means: Voltage drop= electrostatic potential(under bias)-electrostatic potential(zero bias)  am i right?

60

General Questions and Answers / Re: Question about molecular energy spectrum in two-probe

« on: November 21, 2012, 14:52 »

thank you professor Anders