Author Topic: What‘s the difference between the PDOS of a bulk and the PLDOS of a device?  (Read 102 times)

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Offline yeshizhuo

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 :D Dear staffs and users:
 I have a question that really troubles me. I have no idea about the difference between the PDOS of a bulk and the PLDOS of a device, even though I know they don't look quite the same.
I have analyzed two similar quantum dot systems. The first one is a bulk system. The second one is a device system, whose central region is just the same as the bulk one. The extended electrodes are semiconductors. Thus the Fermi level of the electrode locates at the central of forbidden gap. 
The presented difference  is that these discret energy levels in the bulk system can be recognized through its PDOS, but these discret energy levels in the device system can not be recognized though the PLDOS. These discret energy levels are lying the energy range of the forbidden gap of electrodes, and thus they can not be founded in the transmission spectrum. I then tuned the scale of the PLDOS into 'log' format. I did find these discret energy levels, but they are really fuzzy to apart from the background DOS. It means that the PLDOS corresponding to these discret energy levels are very small.  But in a bulk system, the PDOS corresponding to these discrete energy levels are almost the same large as these continuous bands. Is the gap of electrodes cause this difference? But in the bulk system, the quantum dot is also sandwiched by this kind of semiconductor. I really want to know the reason.

Offline yeshizhuo

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 Hi, it is me again.::) I have carefully read the manual about the DeviceDOS in ATK.(https://docs.quantumatk.com/manual/Types/DeviceDensityOfStates/DeviceDensityOfStates.html)
I found this sentence "The DeviceDensityOfStates (DDOS) D(E) is computed via the spectral density matrix ρ(E) = ρL(E)+ρR(E) (cf. The non-equilibrium Green’s function (NEGF) method) where L/R denotes the contribution from the left/right electrode".
I then read the munual of NEGF method.(https://docs.quantumatk.com/manual/NEGF.html#sect2-negf-greenfunction) I found this one "The left density matrix contribution is calculated using the NEGF method as [BMO+02]
DL=∫ρL(ε)f(ε−μLkBTL)dε, whereρL(ε)≡12πG(ε)ΓL(ε)G†(ε)is the spectral density matrix. Note that while there is a non-equilibrium electron distribution in the central region, the electron distribution in the electrode is described by a Fermi function f with an electron temperature TL." I think the Fermi function f causes the difference in the question, right?

Online Petr Khomyakov

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I have not seen your PLDOS, but, in general, one should be aware that PLDOS does not show any states in the central region that do not couple to either left or right electrode states.