how to explain this? is it wrong?

[renren123123]

Recently, I calculated a two-probe system and find its DOS and Transmission Spectrum are like as the figure,  which display a disagreement with each other, how to explain this?  is it wrong? it is noted that all calculation are calculated well to be 1e-5!

[Anders Blom]

The results look fine to me from a numerical perspective. If they are correct physically depends on whether you also made sure to have sufficient k-point sampling, etc. Explaining and understanding the results - the fun and important part - is your job as a scientist

[Nordland]

If you ask me I think that the agreement is pretty strong.
The reason why you want to see both DOS and Transmission Spectrum, is that they are not directly proportional to another.

[renren123123]

Recently, I very want to know the following points:
1. the defination of density of states(DOS), does it stand for the number of the states? what is the intuitional respects?
2. In above figure, there are two DOS peaks in its transmission gap below the Fermi level, how to explain this display? why the difference between DOS and T?

[Anders Blom]

The DOS you refer to is the surface density of states in the two-probe system (i.e. in the electrode). If there's a peak in the DOS it means that there are states available at this energy, but it does not mean that they can be transmitted through the central region. So, a finite DOS doesn't necessarily mean non-zero transmission. Conversely, if there are no states at a particular energy (zero DOS), there can be no transmission at this energy either.

[renren123123]

Thank you for your clear explaination! If some molecular orbitals in middle extended molecule(all atoms in the middle scattering region) are located in the transmission gap, can we say that the orbitals are supressed according to the Transmission spectrum and molecular orbitals in bias window? What is the relation between transmission and molecular orbitals(E)?

[nori]

I strongly recommend that you should calculate the pdos, which is the dos projected on the molecule in the central region of your 2-probe system.
from the pdos, you would be able to realize the relationship between the transmission and the electron state of central region

In most cases, a pdos is more useful for analyzing　physical properties than a dos.
(at least, I believe it !)

[renren123123]

However, yesterday I had calculated the whole scattering region or one except surface atoms, their curves are very like each other. All peaks are included in both consituations.

[nori]

Could you give us the scripts for both SCF and PDOS?

[renren123123]

I have the same PDOS script as the forum. I firstly calculated the SCF to obtain the nc file, later, using the PDOS script to get the PDOS, it is easy!