Messages

31

General Questions and Answers / Re: Wrong bandgap calculated for Cu2O using DFT+U

« on: May 9, 2016, 11:28 »

Yes, in the first reference (http://pubs.rsc.org/en/Content/ArticleLanding/2006/CP/b611969g#!divAbstract ), it is shown that PBE+U (U=7) gives 1.48 eV band gap.

In the second reference (http://scitation.aip.org/content/aip/journal/jcp/131/12/10.1063/1.3231869) PBE+U yields 0.67 eV and argued that PBE+U method fails to predict the correct band gap.

I am surprised by the inconsistencies in literature. The lesson learned is that never trust the literature, trust your own calculation.

32

General Questions and Answers / Re: Wrong bandgap calculated for Cu2O using DFT+U

« on: May 6, 2016, 10:17 »

Sorry, here in this article (http://scitation.aip.org/content/aip/journal/jcp/131/12/10.1063/1.3231869)  state that 'Cuprous oxide (Cu 2 O)
(Cu2O) is an abundant, low cost, nontoxic semiconductor material with a direct band gap of 2.17 eV'  (first sentence of the Introduction).

In any case, 0.62 eV of bandgap I calculated seems bit small.

33

General Questions and Answers / Re: Wrong bandgap calculated for Cu2O using DFT+U

« on: May 6, 2016, 10:05 »

I was referring to the article here: http://pubs.rsc.org/en/Content/ArticleLanding/2006/CP/b611969g#!divAbstract   It is written in the abstract.

34

General Questions and Answers / Wrong bandgap calculated for Cu2O using DFT+U

« on: May 5, 2016, 17:36 »

Hi All,

I want to calculate the bandgap of Cu2O using DFT+U in ATK. I used the script generator. The calculation uses spin polarized PBE with U=7 eV and FHI basis sets. However, I calculated a direct bandgap of 0.62 eV, which is not consistent with the experimental indirect bandgap of 1.4 eV.

I attached my script (results are too big to be attached). I really appreciate if you look at my input files and give me suggestions on how to get a correct bandgap. (Except the suggetions of going to hybrid functionals).

Thank you,
Yasheng

35

General Questions and Answers / Re: LDA+U with OpenMXBasisSet

« on: May 3, 2016, 15:25 »

Hi Jess,

I was confused about this about few weeks, now it is clear that it is a bug.  I look forward for the new version.

If DFT+U works with OMX and the script generator has the problem, can you please show DFT+U implementation with OMX basis sets in a script?   e.g. for copper oxide or nickel oxide.

Thank you for your help.


Regards,
Yasheng

36

General Questions and Answers / Re: LDA+U with OpenMXBasisSet

« on: April 25, 2016, 10:57 »

Hi Anders,

If the U term is set by default with OMX basis set, how do we check the value of U? 
Thanks,

37

General Questions and Answers / LDA+U with OpenMXBasisSet

« on: April 22, 2016, 17:21 »

Hi All,

If we want to do LDA+U calculations using OpenMXBasisSet in ATK, how do we adjust the script to include the hubbard U parameter in basis set?  (demonstration for NiO or CuO shall be fine).

In tutorial http://quantumwise.com/documents/tutorials/latest/NiO_LDA_U/index.html/chap.crystal.ldau.html
FHI basis sets are used.

Thank you.

Regards,
Yasheng

38

General Questions and Answers / Geometry optimization in Extended-Huckel method.

« on: April 22, 2016, 15:10 »

Hi,

When I tried to do geometry optimization with Extented-Huckel method for copper, the word 'OptimizeGeometry' on the script generator appeared as 'OptimizeGeometry'. Does this mean that we cannot do geometry optimize with Extended-Huckel method in ATK?

Regards,
Yasheng

39

General Questions and Answers / Re: LDA+U in ATK

« on: April 21, 2016, 13:26 »

Hi Jess,

This trick works fine for me. I look forward to the new version of ATK.

Thanks for your help and regards,
Yasheng

40

General Questions and Answers / Re: LDA+U in ATK

« on: April 18, 2016, 12:21 »

Hi Jess,

Thank you for your advice. I prepared the input files for Cu/Cu2O interface according to your post. However, calculation stopped with error "Exception: 'tuple' object has no attribute 'element'".

I attached my input files, can you please check and if there is anything wrong in the input? Thanks.

Regards,
Yasheng


 

41

General Questions and Answers / LDA+U in ATK

« on: April 16, 2016, 22:41 »

Hi,

I have some problems with setting up calculations for Cu/Cu2O interface. I want to disable Hubbard U for metallic Cu while I want to use Hubbard U for the Cu atoms in Cu2O.  Can you please give some advice on how to do it?

Regards,
Yasheng

42

General Questions and Answers / question about tutorial

« on: April 12, 2016, 11:32 »

Hi,

I have question about the tutorial on this page:
http://quantumwise.com/publications/tutorials/item/832-elastic-scattering-mean-free-path-mobility-impurity-scattering-in-a-silicon-nanowire

I wonder how can you get one combined nc file for four different calculations.
(dopant 1, dopant 2, dopant 3 and dopant 4 has one nc file named sinw_transmissions_P_dopant_1_2_3_4.nc).

Thanks for your explanation.

Yasheng

43

General Questions and Answers / stoping ATK job

« on: February 23, 2016, 15:45 »

Hi Everyone,

I wonder if there is anyway to stop ATK DFT geometry optimization job just after the coming Force step finished.   Similar thing can be done by using STOPCAR in VASP. 

Thanks,
YM

44

General Questions and Answers / Can we do the geometry optimization and transport properties in one calculation?

« on: February 10, 2016, 11:55 »

Hi All,

Should we first do the geometry optimization, then take the optimized structure to calculate the transport properties?

or

Should we do everything in one calculation?

Thanks.

45

General Questions and Answers / Re: Charged system

« on: February 9, 2016, 16:21 »

Thank you.

What is the difference between defining charge on the scripter and the method mentioned in the following tutorial?

http://quantumwise.com/publications/tutorials/item/820-ni-silicide-si-interfaces

# -------------------------------------------------------------
# Add Doping
# -------------------------------------------------------------
doping_density = 1e+20
# Calculate the volume  and convert it to cm^-3
volume = right_electrode_lattice.unitCellVolume()
volume = float(volume/(0.01*Meter)**3)
# Calculate charge per atom
n_doping = doping_density * volume / len(right_electrode_elements)
# Add external potential to the central region
external_potential = AtomicCompensationCharge([
        ('doping_central_region', n_doping)
        ])
 
central_region.setExternalPotential(external_potential)
# Dope the right electrode
right_electrode.setExternalPotential(
      AtomicCompensationCharge([(Silicon, n_doping)]))


In both methods, we add charge in different ways.