Affinity of MoS2 and MoS2 passivation

[zmisha]

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.

[Umberto Martinez]

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.

2. with C atoms maybe? http://dx.doi.org/10.1088/0957-4484/25/16/165703
It is up to you.

[zmisha]

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! 

[zh]

A serious problem is that the underestimation of band gap of a semiconductor by the LDA/GGA calculations  would affect the obtained results for the affinity of a semiconductor.
So you at first check how much the band gap of a bulk MoS2 is underestimated compared with experimental data.

[zmisha]

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.

[Umberto Martinez]

structure? do you have enough vacuum?
check the work function tutorial for instruction on how to converge properly the potential outside the surface (vacuum level equal zero)

you know the band gap of MoS2 is very much dependent on the number of layers.
which structure your experimental value refers to? a monolayer?

[zmisha]

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.

[Umberto Martinez]

Hi guys,
once again, please provide a reference.
how did they get experimentally 4.2 eV. I mean, it could be that the system is a multilayer MoS2. hardly a single layer.

zmisha: from a quick look to the figures looks like you have a MoS2 nanoribbon? hard to say.

Anuja, it may be a fortunate coincidence
meaning your result is not converged. the structure looks fine besides the vacuum region which looks too small to me.
you can easily check it by increasing the number of k-points, mesh cutoff and vacuum region. Your results should not change (within a certain tolerance of course)