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General Questions and Answers / Re: GGA+U bandstructure calculation of monolayer mos2
« on: March 24, 2017, 16:23 »
Thanks.
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General Questions and Answers / Re: GGA+U bandstructure calculation of monolayer mos2
« on: March 23, 2017, 22:48 »Try a negative value of U instead. The definition of +U is not exactly the same in planewave and LCAO.
Hi,
I want to mention that the ATK version I am using is 13.8.1, since our group only bought the license of this version. Does this give a difference?
I tried to use a negative value of U.
Without U, the GGA-PBE (no spin) gives Eg 1.689eV.
With U=-2eV on d orbital of Mo atom only, the GGA-PBE (no spin) gives Eg 1.698eV.
With U=-3eV on d orbital of Mo atom only, the GGA-PBE (no spin) gives Eg 1.691eV.
I tried U=-3eV or U=3eV on both d orbital of Mo atom and p orbital of S atom. The band gap still did not change much.
Anyway, I did not see a large Eg increase of monolayer MoS2.
However, I did LDA+U (no spin) for orthorhombic phase of HfO2.
Without U, the band gap is 4.03 eV.
With U=5eV on d orbital of both Hf and O atoms, the band gap increases to 5.4eV.
Could you give some suggestions on how to get a correct band gap(around 2eV) of monolayer MoS2 using LDA+U or GGA+U?
Thanks.
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General Questions and Answers / GGA+U bandstructure calculation of monolayer mos2
« on: March 22, 2017, 23:57 »
Dear Sir/Madam,
I used GGA-PBE (no spin) to calculate the band structure of monolayer MoS2. The band gap is 1.689eV.
We know that GGA and LDA underestimate the band gap. And people usually use GGA+U to get the correct band gap.
Then I used GGA+U with U=3eV on d orbital of Mo atom. The band gap decreases to 1.566eV.
Based on reference “Tuning the electronic properties of bondings in monolayer MoS2 through Au O co-doping”, the band gap should increase we use a positive U values. In this reference paper, they uses CASTEP and U(7.5 eV) for Mo 4d orbital (no spin). The band gap increases to 1.97eV.
Although the software is different, but the general trend should be the same, I think.
When I use U=7.5 eV in ATK, the SCF does not converge within 300 steps.
Could you please give some comments on this?
Thanks.
I used GGA-PBE (no spin) to calculate the band structure of monolayer MoS2. The band gap is 1.689eV.
We know that GGA and LDA underestimate the band gap. And people usually use GGA+U to get the correct band gap.
Then I used GGA+U with U=3eV on d orbital of Mo atom. The band gap decreases to 1.566eV.
Based on reference “Tuning the electronic properties of bondings in monolayer MoS2 through Au O co-doping”, the band gap should increase we use a positive U values. In this reference paper, they uses CASTEP and U(7.5 eV) for Mo 4d orbital (no spin). The band gap increases to 1.97eV.
Although the software is different, but the general trend should be the same, I think.
When I use U=7.5 eV in ATK, the SCF does not converge within 300 steps.
Could you please give some comments on this?
Thanks.
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General Questions and Answers / Re: energy independent kappa value in Complex band structure of HfO2
« on: March 20, 2017, 23:30 »
Thanks for your help.
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General Questions and Answers / Re: energy independent kappa value in Complex band structure of HfO2
« on: March 20, 2017, 15:59 »
Hi,
Attachment is the HfO2 phase structure.
I guess what I really want it where the energy independent kappa curve comes from. Or I am not sure how to explain the physics behind it.
Based on the tutorial, the imaginary bands are connected with the real band. But how the energy independent kappa curve connected with the real band?
Attachment is the HfO2 phase structure.
I guess what I really want it where the energy independent kappa curve comes from. Or I am not sure how to explain the physics behind it.
Based on the tutorial, the imaginary bands are connected with the real band. But how the energy independent kappa curve connected with the real band?
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General Questions and Answers / energy independent kappa value in Complex band structure of HfO2
« on: March 20, 2017, 04:18 »
Dear Sir/Madam,
I did complex band structure calculation of HfO2 orthorhombic phase.
I got energy independent kappa curve, which has small value as in attachment(hfo2_complex.tif).
However, I am expecting kappa curve with an elliptic shape as in attachment(WSe2_complex.tif) from a reference paper. "Monolayer Transition Metal dichalcogenide channel-based tunnel transistor." R. K. Ghosh et al.
I do not really understand where is this energy independent kappa curve from or what is the meaning of it.
Could you please give me some comments?
I did complex band structure calculation of HfO2 orthorhombic phase.
I got energy independent kappa curve, which has small value as in attachment(hfo2_complex.tif).
However, I am expecting kappa curve with an elliptic shape as in attachment(WSe2_complex.tif) from a reference paper. "Monolayer Transition Metal dichalcogenide channel-based tunnel transistor." R. K. Ghosh et al.
I do not really understand where is this energy independent kappa curve from or what is the meaning of it.
Could you please give me some comments?
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General Questions and Answers / Re: How to figure out complex band structure at G-K?
« on: February 24, 2017, 22:04 »
We have solved the problem.
For the MoS2 structure in ATK, to get the complex bandstucture along G-K, we should choose the Miller indices (1,1,0) to cleave the surface.
For the MoS2 structure in ATK, to get the complex bandstucture along G-K, we should choose the Miller indices (1,1,0) to cleave the surface.
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General Questions and Answers / Re: How to figure out complex band structure at G-K?
« on: February 23, 2017, 16:58 »
I have the same question for complex band structure.
In the example of complex band structure calculation of Si. You choose the surface with (1,0,0) so that the reciprocal lattice vector kc is along X direction.
Here, you said that we need to cleave the MoS2 unit cell such that the reciprocal point K (1/3, 2/3, 0) is perpendicular to the AB-plane.
In this case, how should we cleave the MoS2? I tried to use miller indices (1,2,3) (1,2,0) to get the surface.
But it does not work.
Could you please give more detail?
Thanks.
In the example of complex band structure calculation of Si. You choose the surface with (1,0,0) so that the reciprocal lattice vector kc is along X direction.
Here, you said that we need to cleave the MoS2 unit cell such that the reciprocal point K (1/3, 2/3, 0) is perpendicular to the AB-plane.
In this case, how should we cleave the MoS2? I tried to use miller indices (1,2,3) (1,2,0) to get the surface.
But it does not work.
Could you please give more detail?
Thanks.
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General Questions and Answers / Re: Affinity of MoS2 and MoS2 passivation
« on: May 20, 2014, 20:19 »
Sir,
And this is MoS2 monolayer.
Sorry, I do not know how to insert image of my structure. I add the image of top view of MoS2 to the attachment.
The top vacuum and bottom vacuum are both 30 angstrom, which is long enough. The K point is 1x9x1, because is monolayer, so k point in A direction is 1. Others are the same as the work function tutorial.
The work function I got is 5.6 eV. As the band gap of MoS2 monolayer is 1.8 eV, the affinity of MoS2 is 5.6-0.9=4.7 eV. But this is bigger than the experimental value 4.2 eV.
Is 4.7 eV the supposed result in ATK-LDA, or I calculated it in a wrong way?
Thanks for your time.
And this is MoS2 monolayer.
Sorry, I do not know how to insert image of my structure. I add the image of top view of MoS2 to the attachment.
The top vacuum and bottom vacuum are both 30 angstrom, which is long enough. The K point is 1x9x1, because is monolayer, so k point in A direction is 1. Others are the same as the work function tutorial.
The work function I got is 5.6 eV. As the band gap of MoS2 monolayer is 1.8 eV, the affinity of MoS2 is 5.6-0.9=4.7 eV. But this is bigger than the experimental value 4.2 eV.
Is 4.7 eV the supposed result in ATK-LDA, or I calculated it in a wrong way?
Thanks for your time.
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General Questions and Answers / Re: Affinity of MoS2 and MoS2 passivation
« on: May 19, 2014, 20:43 »
Sir,
The band gap of MoS2 in ATK is 1.8 eV using LDA, and the experimental value is 1.95 eV. The affinity of MoS2 in ATK should be smaller than the experimental affinity of MoS2, theoretical.
However, the affinity i calculated using ATK-LDA is 4.7 eV, which is larger than 4.2 eV, the experimental affinity of MoS2.
So I think I calculated it in the wrong way.
Could you give me some advice?
Thanks for your time.
The band gap of MoS2 in ATK is 1.8 eV using LDA, and the experimental value is 1.95 eV. The affinity of MoS2 in ATK should be smaller than the experimental affinity of MoS2, theoretical.
However, the affinity i calculated using ATK-LDA is 4.7 eV, which is larger than 4.2 eV, the experimental affinity of MoS2.
So I think I calculated it in the wrong way.
Could you give me some advice?
Thanks for your time.
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General Questions and Answers / Re: Affinity of MoS2 and MoS2 passivation
« on: May 16, 2014, 22:06 »1. here it is explained: http://quantumwise.com/forum/index.php?topic=2820.0#.U3ZJBnWSzh8
I am not sure it is the topic you refer.
This is the topic I refer. In this topic, you said i can "follow the calculation procedure of work function of a metal using the slab supercell to estimate the electron affinity of a semiconductor." And i followed the procedure and tried to calculate the affinity of MoS2. But the result does not make sense. I need to know the affinity of MoS2 in ATK. Is it 4.2 eV? Or could you tell me a right way to calculate the affinity of a semiconductor?
Thank you, sir!
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General Questions and Answers / Affinity of MoS2 and MoS2 passivation
« on: May 14, 2014, 21:49 »
Sir,
1. Could you tell me how to calculate the affinity of MoS2? I tried to follow the calculation procedure of work function of a metal, like you said in this topic http://quantumwise.com/forum/.U3PFlfldUwA. But the result does not quite make sense. Or could you tell me if the affinity of MoS2 is 4.2 eV, which is published data?
2. How to passivate the dangling bond of MoS2? You said "the passivation of dangling bonds in MoS2 by hydrogen may not make sense for some cases, e.g., the dangling bonds around Mo atoms. " in this topic http://quantumwise.com/forum/index.php?topic=1241.msg6068#msg6068. Then is there another material that i can use to passivate MoS2?
Thank you very much.
1. Could you tell me how to calculate the affinity of MoS2? I tried to follow the calculation procedure of work function of a metal, like you said in this topic http://quantumwise.com/forum/.U3PFlfldUwA. But the result does not quite make sense. Or could you tell me if the affinity of MoS2 is 4.2 eV, which is published data?
2. How to passivate the dangling bond of MoS2? You said "the passivation of dangling bonds in MoS2 by hydrogen may not make sense for some cases, e.g., the dangling bonds around Mo atoms. " in this topic http://quantumwise.com/forum/index.php?topic=1241.msg6068#msg6068. Then is there another material that i can use to passivate MoS2?
Thank you very much.
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General Questions and Answers / Re: Question about calculating Work function of metal
« on: May 9, 2014, 22:44 »
Thank you sir.
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General Questions and Answers / Question about calculating Work function of metal
« on: May 7, 2014, 22:37 »
Hello Sir,
http://quantumwise.com/publications/tutorials/mini-tutorials/134 is the tutorial that how to calculation the Work function.
I followed the tutorial and tried to calculate the work function of Ag-111.
What I don't understand is the choice of top vacuum length and bottom vacuum length. When i use Top vacuum = 20 Å and Bottom vacuum = 5 Å, which is the same as the tutorial, the Work function is 4.775822 eV. But when i use Top vacuum = 35 Å and Bottom vacuum = 30 Å, 4.758183 eV.
Could you tell me why different vacuum length and bottom vacuum length give different result?
Thanks for your time.
http://quantumwise.com/publications/tutorials/mini-tutorials/134 is the tutorial that how to calculation the Work function.
I followed the tutorial and tried to calculate the work function of Ag-111.
What I don't understand is the choice of top vacuum length and bottom vacuum length. When i use Top vacuum = 20 Å and Bottom vacuum = 5 Å, which is the same as the tutorial, the Work function is 4.775822 eV. But when i use Top vacuum = 35 Å and Bottom vacuum = 30 Å, 4.758183 eV.
Could you tell me why different vacuum length and bottom vacuum length give different result?
Thanks for your time.
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