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Messages - Shan

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16
General Questions and Answers / problem displaying Bandstructure of Graphene: VNL as QE GUI
« on: January 4, 2017, 19:43 »
Dear QW Team,

I am using VNL as GUI for Quantum Espresso. First, I implemented the tutorial of Silicon, VNL worked fine for me.

When I went on to Graphene (two atoms) bandstructure calculation, the VNL shows empty band structure plot. However, when I plot the same using GNUPLOT it shows perfect  bandstructure and zero band gap.

Why VNL could not show band structure of Graphene, however it is working fine in displaying DOS plot of graphene. I really wasted a lot of time thinking that the problem is with my calculation.
Please clarify.

Thank you very much for your time.

17
General Questions and Answers / Re: Mulliken charges, Wrong Prediction by ATK
« on: September 28, 2016, 07:55 »
well, thanks a lot for such clear reply Dr. Anders,

I was aware that mulliken is not as accurate as Natural population analysis. However, as mentioned earlier, it  was not the quantity of the charge that bothered me, but the direction of charge.

If possible, please fix the issue in the upcoming version.

Have a good day sir.

18
General Questions and Answers / Re: Mulliken charges, Wrong Prediction by ATK
« on: September 27, 2016, 14:03 »
Dear Dr. Anders,
Here are the raw log data from both ATK and Gaussian. (Gaussian DFT chemical package is based full potentials and is well recommended package for molecular analysis)

From ATK:
Quote
# Title: NO2.nc - gID002
# Type:  MullikenPopulation
+------------------------------------------------------------------------------+
|                                                                              |
| Mulliken Population Report                                                   |
|                                                                              |
| ---------------------------------------------------------------------------- |
|                        |                                                     |
| Element   Total  Shell | Orbitals                                            |
|                        |                                                     |
|                        |      s                                              |
|   0   N   5.123  0.113 |  0.113                                              |
|                        |      y      z      x                                |
|                  0.473 |  0.141  0.147  0.185                                |
|                        |      s                                              |
|                  1.319 |  1.319                                              |
|                        |      y      z      x                                |
|                  2.991 |  1.168  0.897  0.927                                |
|                        |     xy     zy  zz-rr     zx  xx-yy                  |
|                  0.099 |  0.034  0.003  0.009  0.021  0.032                  |
|                        |     xy     zy  zz-rr     zx  xx-yy                  |
|                  0.129 |  0.043  0.006  0.009  0.035  0.035                  |
|                        | --------------------------------------------------- |
|                        |      s                                              |
|   1   O   5.939  0.097 |  0.097                                              |
|                        |      y      z      x                                |
|                  0.538 |  0.182  0.200  0.157                                |
|                        |      s                                              |
|                  1.545 |  1.545                                              |
|                        |      y      z      x                                |
|                  3.723 |  1.294  1.235  1.194                                |
|                        |     xy     zy  zz-rr     zx  xx-yy                  |
|                  0.011 |  0.003  0.001  0.001  0.003  0.003                  |
|                        |     xy     zy  zz-rr     zx  xx-yy                  |
|                  0.025 |  0.008  0.002  0.003  0.006  0.007                  |
|                        | --------------------------------------------------- |
|                        |      s                                              |
|   2   O   5.938  0.097 |  0.097                                              |
|                        |      y      z      x                                |
|                  0.538 |  0.193  0.200  0.145                                |
|                        |      s                                              |
|                  1.545 |  1.545                                              |
|                        |      y      z      x                                |
|                  3.722 |  1.386  1.235  1.101                                |
|                        |     xy     zy  zz-rr     zx  xx-yy                  |
|                  0.011 |  0.007  0.000  0.001  0.004 -0.000                  |
|                        |     xy     zy  zz-rr     zx  xx-yy                  |
|                  0.025 |  0.007  0.000  0.003  0.007  0.008                  |
+------------------------------------------------------------------------------+


From Gaussian,
Quote
Summary of Natural Population Analysis:                 
                                                         
                                       Natural Population
                Natural  -----------------------------------------------
    Atom  No    Charge         Core      Valence    Rydberg      Total
 -----------------------------------------------------------------------
      N    1    0.47932      1.99977     4.48234    0.03856     6.52068
      O    2   -0.24115      1.99989     6.23083    0.01043     8.24115
      O    3   -0.23817      1.99989     6.22784    0.01043     8.23817
 =======================================================================
   * Total *    0.00000      5.99956    16.94102    0.05943    23.00000


the same have been attached to this post.

Awaiting your reply,
Shan

19
General Questions and Answers / Re: Mulliken charges, Wrong Prediction by ATK
« on: September 27, 2016, 09:22 »
Dear Dr. Jeff  and Dr. Anders

I was not wrong in interpreting the signs of mulliken population. below are the original mulliken population shown by atk-dft on NO2,
N   5.123
O   5.939
O   5.938
As per my knowledge these mulliken populations indicate charge gaining of nitrogen and losing of oxygens. aren't they?
(Theory used, ATK-DFT, GGA-RPBE, DZDP)

Whereas the same calculation of NO2 through gaussian (Theory used: DFT, B3LYP, LANL2DZ) as mentioned earlier
N   0.479e (lost)
O  -0.241e   (gained)
O  -0.238e   (gained)

similarly, the Mulliken populations extracted for NH3 using ATK-DFT are,
N   4.842
H   1.053
H   1.053
H   1.053
This shows, charge gained by hydrogens and lost by nitrogen.

However the same using gaussian shows,
N -1.167 (gained)
H  0.389 (lost)
H  0.389 (lost)
H  0.389 (lost)

As I mentioned earlier, this type of contradictory results are observed through ATK several times by me.
There may be variations in quantity of charge due to level of theory used. But, variation in sign (charge transfer direction) is not acceptable.

awaiting your reply,
shan

 

20
General Questions and Answers / Mulliken charges, Wrong Prediction by ATK
« on: September 25, 2016, 19:37 »
Dear QW team,
Wishes of the Day.

I like to report a problem that I encountered several times. ATK could not predict the mulliken charges correctly. Most of the times it gives completely wrong mulliken results.
For example, the mulliken charges extracted using ATK-DFT for NO2 molecule are
N  -0.123e  (gained)
O  +0.062e (lost)
O  +0.062e (lost)

The same using Gaussian09 DFT package gives,
N  +0.479e (lost)
O  -0.241e   (gained)
O  -0.238e   (gained)

This type of complete contradictory results in case of mulliken population were witnessed several times by me.

Awaiting your reply.
Shan 

21
General Questions and Answers / Re: bond length of Carbon bond in graphene using DFT
« on: April 28, 2016, 09:16 »
use "Z-matrix" option that appears in the "Coordinate tools" of Builder. click on the two atoms between which you want to calculate the bond length holding ctrl button.

22
General Questions and Answers / Re: Thermoelectric properties for bulk fcc
« on: March 30, 2016, 12:41 »
I am not interested in device part for now... I stuck to the bulk part sir.

23
General Questions and Answers / Thermoelectric properties for bulk fcc
« on: March 30, 2016, 08:33 »
Hello QW team...

I am trying to calculate the thermoelectric properties of BN (bulk FCC) structure. I went though the tutorial  https://quantumwise.com/documents/tutorials/latest/Phonon/index.html/chap.thermoelectric.html

However, to calculate these properties using this tutorial, phonon transmission spectrum and transmission spectrum are needed. Which i couldn't find in the script generator when i added BN bulk crystal.

Please tell me how can i calculate the thermoelectric properties for this bulk material.


Thank you very much for ur time...  and Wish you a wonderful day.

24
General Questions and Answers / Re: "Area of cross section" of Atomic chain
« on: March 10, 2016, 08:17 »
Dear sir,

1) If conductivity does not include area, the new units of conductivity will be s-m instead of s/m.  Will it be valid???

2) I have computed I-V curve for the LAC, does it include the scattering mechanisms (i.e phonons etc) by default ??. If not, how to include them in the I-V calculation.

Thank you very much for ur time sir.

25
General Questions and Answers / Re: "Area of cross section" of Atomic chain
« on: March 9, 2016, 09:31 »
Then, How can I calculate the quantum conductivity for the atomic chain sir.

Plz help me. Thank you very much for ur time sir.

26
General Questions and Answers / Re: Strain calculation from stress tensor
« on: March 9, 2016, 09:20 »
thank you Dr. Zh

27
General Questions and Answers / "Area of cross section" of Atomic chain
« on: March 8, 2016, 16:28 »
Dear sir,

I want to calculate the resistivity (rho = R*A/l)) of an atomic chain, for that I need to calculate area of cross section first. I am really confused, on how to calculate the area of cross section for the atomic chain. (structure is shown in the figure)

plz help sir. Thank you very much for your time.

28
General Questions and Answers / Re: Strain calculation from stress tensor
« on: March 8, 2016, 14:37 »
So...   

(a1-a0)/a0  is strain tensor, a unit less quantity...?

29
General Questions and Answers / Re: Strain calculation from stress tensor
« on: March 3, 2016, 17:13 »
Dear sir,

I tried to calculate the stiffness coefficient as shown in the below image,  the procedure adopted is-

stiffness coefficient = (force applied)/(displacement produced),                         [displacement in z-direction = 1.2662 Ang]

The force applied is calculated from the stress tensor, F = (sigma)*(cross sectional area)

1) Please verify the procedure sir... whether the procedure I followed to calculated stiffness coefficient is correct?
2) How can I calculate strain tensor (in Z direction) by using this stiffness coefficient? (I also uploaded the elastic constants and stress tensor results before and after applying stress on the nanowire)

Thank you very much for your time sir.



30
General Questions and Answers / Strain calculation from stress tensor
« on: March 2, 2016, 17:49 »
Dear sir,

I have applied tensile stress on BN nanowire by increasing the size of supercell in the periodic direction (z-direction).
The computed stress tensor in z-direction before and after applying stress are 0.0377 and 0.152 eV/A^3.

1) How can I calculate the strain tensor in z-direction from the above computed stress tensor?
2) The percentage increase in stress in the above case is 303 %, Is the percentage increase in strain will also be 303 % ? (I read in some sources that strain is directly proportional to stress) 


Please clarify sir.  Thank you very much for your time.

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