some question about the DOS

[Roc]

Dear everyone,

When I probe my two-probe system, I calculate the "Density of atates", how to understand
 the "Density of atates" (it is of the molecule or central scattering region or....), When I set it from-2eV to 2eV like the attachment1, I get the DOS like attachment2, Does the energy point 0eV mean the Fermi level. Another, my molecule has high symmetry, is the DOS distrustful? 

That seems that the current version couldn't calculate the PDOS, could someone write one script for it.


Thanks!

[Nordland]

The fermi level is 0 eV.

I think that getting the PDOS requires a lot of tweaking - however I can have a look at it, if there is any way to do it, once I get some spare time on my hands.
However It dont see any sign of why your DOS should be distrustful. If you compare it with your transmission, you will have obtained valuable information about
the mechanisms of transport in your system.

[Anders Blom]

Getting the PDOS is, in principle, not very difficult, however ATK is not prepared for it, and to do it in a script would therefore require quite a lot of tweaking, indeed... It is something that can be looked into however.

One thing to clarify is what is meant by the PDOS. Some people refer to it as the density matrix projected on specific atoms and orbitals, others prefer it to mean the real-space density (projected in the same way).

As for what the DOS "is", it is the total surface density of states for the complete two-probe system. Thus it is a composite DOS of the band structure of the electrodes and the localized levels of the molecule (broadened by the coupling to the electrodes).

Technically it's computed from the Green's function, and thus it is accurate and trustworthy on the same level as the transmission spectrum and current.

[Nordland]

I have found the a old plot of the density of states for a molecule C6H4S2 molecule.

[Roc]

I have also upload the Transmission spectra under zero bias.

How can I explain it with the DOS. Need I use the HOMO、LUMO to explain it , how to know the HOMO and LUMO through the DOS, there are  many different HOMO and LUMO including calculating single molecule or two-probe system MPSH (molecule and central scattering region) , that's puzzling.


Thanks,

[ipsecog]

You mention that the molecule has symmetries, so are your electrodes metal surfaces like Au [111] or so? If so, you probably need some k-point sampling to describe the surfaces correctly, but your initial post seems to indicate that your use only a single k-point for the DOS calculation. What you get then is just the Gamma point contribution to the DOS (and similarly to T(E)).

[Nordland]

I assume you are having some kind of 1D system of monoatomic wire (Alternative a metallic surface of some kind). If you have the transmission spectrum for the perfect wire we would have the complete picture, but I have a pretty good idea on how it will look.

Comparing all these three graphs I think you are dealing with a ballistic transport of electrons, but I could be wrong. If this is the case, the molecule either
is insulator to create a wall for the electrons to bounce off, or alternative (metallic surface case) the electrons bounce of the wall of the metallic surface and the molecule only works as a vacuum seperator.

[Nordland]

To anyipeng and others.

If I made draw your attention to another post I have made. I have implemented a function for calculating the project density of states in ATK.
It can be found here.

[Roc]

Thanks, Nordland.

Great job!