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Non-equlibrium
Date: 2016/11/18 14:59
Name: Adalicia

Dear Openmx Users,
I have one basic question regarding non-equilibrium situation in Openmx. We are using NEGF to calculate the quantities like transmission etc. The NEGF is used when the system is in non-equilibrium. Where from does the non-equilibrium appear in the problem? Is it because of the initial charge densities we assign for the leads and central region (at the interface of lead and central region)? In defining the initial charge densities we define something like following:
1) Left lead: we keep difference between up and down spin densities
2) Central region: we keep almost equal or exactly equal distribution of initial spin up and down densities
3) Right lead: similar as LEFT LEAD

So the non-equilibrium is occurring at the interface of 1) and 2), and 2) and 3) because of the much difference between the initial densities between the left lead-central region-right lead.

Your comments and suggestions would be highly appreciated.


Thanking you.
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Re: Non-equlibrium ( No.1 )
Date: 2016/11/18 18:30
Name: Artem Pulkin

I did not understand the second part of your question since, generally speaking, equilibrium has nothing to do with spin degree of freedom in particular. Otherwise this is what is supposed to be 'non-equilibrium':

1. The Non-Equilibrium Greens Function is a particular matrix describing the central region. It is hard for me to say why is it called 'non-equilibrium' but there is also an equilibrium Green's function describing bulk leads. Probably, people call it like that to emphasize the difference: there is a bulk and there is a surface/edge/scattering region. (I am not sure about these statements, though).

2. There may also be an applied bias driving system out of equilibrium. Ofc, when you apply a voltage your charge carriers and, thus, the charge density are supposed to move between the leads. This means that your (central region) charge density is out of equilibrium. However, it is a sort of a stationary state since, by fact, the charge density is constant in time and space.
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