Topics

1

General Questions and Answers / Why the conductance is independent on the length of nanowire?

« on: November 28, 2012, 23:52 »

Hi everyone:
I calculated the conductance of Li-wires with different lengths and found that the values of conductance are almost the same. But as I know, the electrical conductivity is a material property and indepedent on the length and cross section of the material. However, the conductance, which equals conductivity*(cross section)/length, should be inversely proportional to the length. Could someone tell me why my calculated conductance is independent on the length?
Thanks very much! 

2

General Questions and Answers / Is the gate added correctly?

« on: August 28, 2012, 16:27 »

Hi everyone,
I'm now considering studying the conductance of a device with H+ involved. The geometry is included in the file Pt.py. In order to simulate the H+, I add a gate just on the bottom of the atom H. By adjusting the gate, the atom H can be turned into H+. But I'm not sure whether it is reasonable using this method. In addition, what boundary condition should I use in this case?
Any suggestion would be appreciated. Thank you very much!

3

General Questions and Answers / How to calculate the charge transfer?

« on: August 6, 2012, 03:00 »

Hi everyone:
In this topic, http://quantumwise.com/forum/index.php?topic=369.0, the author calculated the charge transfer in the system. I'm also studying the effect of the gate voltage on the charge of the central region in a two-probe system. I know that the mulliken population can give the charge of an given atom. Is there another way to calculate the charge transfer?
Any advice would be appreciated!

4

General Questions and Answers / Puzzled about the transmission change when bias voltage is added?

« on: July 29, 2012, 17:33 »

Hi everyone,
I am puzzled about one issue in the two-probe system. When I add voltages of -0.5V and +0.5V to the left and right electrodes, respectively, the Fermi level of the left electrode is shifted up and  the right is shifted down. When calculating the transmission, I think it is more easier for the electrons to transfer from left to right, which should lead to a larger transmission at the Fermi level. But in my calculation, the value is decreased. On the other hand, when I add a voltage of +0.5V and -0.5V to the left and right electrodes, respectively, the value is increased. I'm puzzled by the results. Could anyone help me? Thanks!

5

General Questions and Answers / Not physically reasonable in mulliken population

« on: July 21, 2012, 18:19 »

Hi everyone,
I want to use the ATK to calculate the mulliken population, so I did a simple test on a HCl molecule. The result is:
 Mulliken Population Report                                                   |
|                                                                              |
| ---------------------------------------------------------------------------- |
|                        |                                                     |
| Element   Total  Shell | Orbitals                                            |
|                        |                                                     |
|                        |      s                                              |
|   0   H   1.044  0.129 |  0.129                                              |
|                        |      s                                              |
|                  0.773 |  0.773                                              |
|                        |      y      z      x                                |
|                  0.142 |  0.058  0.042  0.042                                |
|                        | --------------------------------------------------- |
|                        |      s                                              |
|   1  Cl   6.956  0.090 |  0.090                                              |
|                        |      y      z      x                                |
|                  0.630 |  0.153  0.239  0.239                                |
|                        |      s                                              |
|                  1.674 |  1.674                                              |
|                        |      y      z      x                                |
|                  4.525 |  1.091  1.717  1.717                                |
|                        |     xy     zy  zz-rr     zx  xx-yy                  |
|                  0.037 |  0.002  0.002  0.008  0.000  0.025                  |
+------------------------------------------------------------------------------+
But as is know, for the HCl, the result should be H+ and Cl- and the electrons for H and Cl should be 0.0 and 8.0, respectively.
My input file is:
# -------------------------------------------------------------
# Bulk configuration
# -------------------------------------------------------------

# Set up lattice
vector_a = [10.0, 0.0, 0.0]*Angstrom
vector_b = [0.0, 10.0, 0.0]*Angstrom
vector_c = [0.0, 0.0, 9.999945]*Angstrom
lattice = UnitCell(vector_a, vector_b, vector_c)

# Define elements
elements = [Hydrogen, Chlorine]

# Define coordinates
cartesian_coordinates = [[ 5.       ,  4.36     ,  4.9999725],
                         [ 5.       ,  5.64     ,  4.9999725]]*Angstrom

# Set up configuration
bulk_configuration = BulkConfiguration(
    bravais_lattice=lattice,
    elements=elements,
    cartesian_coordinates=cartesian_coordinates
    )

# -------------------------------------------------------------
# Calculator
# -------------------------------------------------------------
#----------------------------------------
# Basis Set
#----------------------------------------
basis_set = GGABasis.DoubleZetaPolarized

#----------------------------------------
# Exchange-Correlation
#----------------------------------------
exchange_correlation = GGA.PW91

numerical_accuracy_parameters = NumericalAccuracyParameters(
    k_point_sampling=(10, 10, 10),
    )

calculator = LCAOCalculator(
    basis_set=basis_set,
    exchange_correlation=exchange_correlation,
    numerical_accuracy_parameters=numerical_accuracy_parameters,
    )

bulk_configuration.setCalculator(calculator)
nlprint(bulk_configuration)
bulk_configuration.update()
nlsave('HCl.nc', bulk_configuration)

# -------------------------------------------------------------
# Mulliken population
# -------------------------------------------------------------
mulliken_population = MullikenPopulation(bulk_configuration)
nlsave('HCl.nc', mulliken_population)
nlprint(mulliken_population)

Could anyone give me any suggestions? Look forward to your reply! Thanks!