Bias window identifcation help

[Khattab]

Dear All,
Now, i calculated I-V curve of some organic molecules, and i want to interpret these curves with the aid of transmission spectrum curves, i read all questions about transmission spectrum and bias window in quantum forum and i clearly understand that the current is the integration of transmission spectrum at given voltage, and the integration limits are chemical potential for left and right electrode this according to Landauer-Buttiker formula , now when i calculated the transmission spectrum at 4 volt i set the voltage of one electrode at 0 volt and the voltage of the other electrode is 4 volt in this case, what is the bias window for this cas and  how can i identify bias window at the transmission spectrum curve  ?
Waiting for your replay as soon as possible,
Thanks in advance,
Khattab

[Anders Blom]

It's from -2 to 2 eV. If you plot it in VNL in the IV curve analyzer it's the blue part of the curve.

[Khattab]

Dear Dr Anders Blom,
Thank you very much for your answer, but could you till me how to calculate bias widow for any bias voltage for example, 1, 2 or 3
Regards,
Khattab

[Anders Blom]

It's always -bias/2 to +bias/2.
See http://quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/ref.transmissionspectrum.html for lots of useful information.

[Khattab]

Dear Dr Anders Blom,
Firstly thank you very much for your rapid response of my questions, I read the page you sent , and this is the part about bias window,

electrode_voltages

    The electrode voltages to be used for defining the bias window for the current calculation. If no voltage is specified it will use the voltages in the self-consistent calculation. If voltages are specified the current will be obtained non-self-consistent.

    Type: Must be given as 2 voltages - for example, [-0.5, 0.5]*Volt.
    Default: If no electrode voltages are specified the same voltages will be used as those set on the calculator for the electronic structure calculation

yes i understand that bias voltage used to identify bias window, but my question is, if i use electrode voltage from 0 to 2 this mean bias window from 0 to 2 also??
from my information , bias window is chemical potential of left and right electrode??

Thanks in Advance
Khattab   

[Anders Blom]

If we for now assume there are no gates in the system, which makes it more complex, then it's quite simple: you specify the electrode voltages in the input file, but only the difference between them matter - the difference is the bias. So if you set both electrodes to +5 V, it's still zero bias, if set one to +1 V and one to -1 V, it's 2 V, but so is 19 V and 17 V.

When we compute the transmission spectrum, the energy zero point is chosen at (VLeft+VRight)/2. Therefore the "bias window" is always -bias/2 to +bias/2.

[Khattab]

Dear dr  anders blom,
Thank you very much for you time and your effort to reply my questions ,  now I clearly understand that in simple cases like two probe system in order to idenyify bias window  we divide voltage of left and right electrode by 2.
Thank you very much
Khattab

[Khattab]

Dear dr  anders blom,
Thank you very much for you time and your effort to reply my questions , according to your answe bias window is the rang of -bias/2 to + bias/2, i follow this rule but during writing my paper i found paper which say that bias window is the limits of bias window, and is calculated from this equations

  µL = EF-eVb/2 and µR = EF+ eVb/2

 now i confused , if i the applied bias on left electrode is 2V and on right electrode is 0V , according to your answer bias window is the range from 0 to 1 ev and according to equations above the bias window is form 0 to -1    , what is true 
waiting for your answer as soon as possible
Thanks in advance
Khattab

[Anders Blom]

No, according to all expressions and comments and equations the bias window is then from -1 to +1. Vb is the BIAS, not the electrode voltages (Vb=Vleft-Vright)

[Khattab]

No, according to all expressions and comments and equations the bias window is then from -1 to +1. Vb is the BIAS, not the electrode voltages (Vb=Vleft-Vright)

Dear Dr anderson,
you say Vb=Vleft-Vright
            Vb= 2-0
            Vb= 2
from this equation  µL = EF-eVb/2 and µR = EF+ eVb/2
                                          µL= 0-2/2
                                             = -1        EF= 0eV
And                                    µR = 0 + 2/2
                                             = +1
                               so bias window is  from +1 to -1   is this right

can i consider only region from 0 to +1 as applied positive bias only
Thanks in advance,
Khattab
                                                    

[Anders Blom]

No

[Khattab]

Thank you Dr Anderson