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Date: 2017/01/24 15:16
Name: hamed   <>

dear all

I want to calculate I-V for my device. The channel is different from Leads(C0 ≠ L0).

1-Should i add or merge C0 with L0 and make a bigger C0?(for example (new C0 = (L0L0C0R0R0))

2-How should i relax or vc-relax this device?

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Re: negf-vcrelax ( No.1 )
Date: 2017/01/24 19:10
Name: Artem Pulkin

1. Yes, it is generally a good idea.
2. You should embed your "L0L0C0R0R0" into periodic boundary conditions and relax it as usual. I.e. relax something like "R0C1L0L0L0C0R0R0". Without NEGF, of course.
Re: negf-vcrelax ( No.2 )
Date: 2017/01/25 01:06
Name: hamed  <>

Dear sir

At first thanks for your answer

|-Do you think that i must follow the below steps for optimization or not?please explain

1-VC-relax of Leads(R0,L0)
2-VC-relax of center(L0L0C0R0R0)
3-VC-relax of device (

||- Sorry but i did not understand " relax something like "R0C1L0L0L0C0R0R0". Without NEGF, of course."

your assistance in this matter is greatly appreciated
Re: negf-vcrelax ( No.3 )
Date: 2017/01/26 01:17
Name: Artem Pulkin

Regarding 1): yes.

Regarding everything else:

The point is that the NEGF calculation is too slow and too computationally demanding for relaxing your structures. To relax, you typically use supercell models with your defect. It is fairly simple if L0 = R0, i.e. you have the same lead material at both sides. In this case you, literally, change NEGF to BAND in the input file and do the relaxation.

Now, if your L0 is not the same as R0, you have to relax two defect at once. The first one is


And the second one is


You join them into a supercell like this


and relax it. Why do you have to do it? Because you have periodic boundary conditions in the supercell. I.e. your leftmost and rightmost units (L0 in the above case) have to be same. It is not the case if you relax your transport model [L0L0C0R0R0].

Re: negf-vcrelax ( No.4 )
Date: 2017/01/27 00:32
Name: hamed  <>

thanks for your help and guidance
Re: negf-vcrelax ( No.5 )
Date: 2017/01/27 01:09
Name: kim

What is the difference between C0 and C1?
Re: negf-vcrelax ( No.6 )
Date: 2017/01/27 20:55
Name: Artem Pulkin

It is a very relevant question. For example, if both L0 and R0 are inversion-symmetric, you may use a mirror-symmetric C0 as a C1. However, in a more general case you invent one more defect between the same materials (but different terminations). It should be as chemically neutral as it is possible.

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