Gate-Drain curves of p-doped ZnSe

[beauyy]

Dear sir,
        I am calculating the gate-drain curves of ZnS devices doped with MoO3 molecule. All the calculation at different gate voltage is SCF converged. But the drain current does not monotonously decrease with the rise of gate voltage. Is there any errors in this calculation？All the currents are calculated from the device configuration at lower gate voltage.

     The .py is listed as following:
#read in the old configuration                                                                                   
device_configuration = nlread("F:/MoO3/gate-ZnS-MoO3-0.8V-b0.4V.nc",object_id='gID000')[0]                       
calculator = device_configuration.calculator()                                                                   
metallic_region0 = device_configuration.metallicRegions()[0]                                                     
                                                                                                                 
# Define gate_voltages                                                                                           
gate_voltage_list=numpy.linspace(0.6,0.6,1)*Volt                                                                 
                                                                                                                 
for gate_voltage in gate_voltage_list:                                                                           
    device_configuration.setMetallicRegions(                                                                     
        [metallic_region0(value = gate_voltage)] )                                                               
                                                                                                                 
    # make a copy of the calculator and attach it to the configuration                                           
    # restart from the previous scf state                                                                         
    device_configuration.setCalculator(calculator(),                                                             
         initial_state=device_configuration)                                                                     
    device_configuration.update()                                                                                 
    nlsave('F:/MoO3/gate-ZnS-MoO3-0.8V-b0.6V.nc', device_configuration)                                           
                                                                                                                 
    #Analysis                                                                                                     
    filename= 'F:/MoO3/gate-ZnS-MoO3-0.8V-b0.6V.nc'                                                               
    transmission_spectrum = TransmissionSpectrum(                                                                 
        configuration=device_configuration,                                                                       
        energies=numpy.linspace(-2,2,101)*eV,                                                                     
        kpoints=MonkhorstPackGrid(5,5),                                                                           
        energy_zero_parameter=AverageFermiLevel,                                                                 
        infinitesimal=1e-06*eV,                                                                                   
        self_energy_calculator=RecursionSelfEnergy(),                                                             
        )                                                                                                         
                                                                                                                 
    nlsave('F:/MoO3/gate-ZnS-MoO3-0.8V-b0.6V.nc', transmission_spectrum,object_id='trans'+str(gate_voltage))     
    nlprint(transmission_spectrum)                                                                               

The device configuration is attached.


                                                                                                                 
                                                                                                                 
                                                                                                                 

       

[Umberto Martinez]

Can you include also you original script that generated gate-ZnS-MoO3-0.8V-b0.4V.nc?
hard to judge from a picture. However:
- do you have Neuman boundary conditions along B direction? This is because of the gate region.
- The central region is definitely too short.
- Also you need a bigger vacuum region around your device.

[beauyy]

Dear sir,
    I have attached the device .py  below. The neuman boundary conditions is applied along B direction.
   Of course, I am willing to make the central region longer, but it is difficult to converge.
   And the bigger vacuum region is also make the device more difficult to converge. 

[Umberto Martinez]

Please include the calculator part.
You may need to try to increase k-point sampling.
Also, it seems that your configuration has a smaller periodicity along A. This means you can probably reduce the size of your cell along this direction.

[beauyy]

The calculation part and device part have been included in the .py file attached below. The k-point in calculation is 5*5*100. It is large enough for this calculation. And the size along A direction seems impossible to be reduced. Is there anything wrong in my calculation?

[Umberto Martinez]

You may have your reasons to use this supercell (such as creating defects) but your structure seems to have a smaller periodicity as indicated in the attached figure.

I definitely suggest you to increase your basis set. A simple SingleZeta basis set is way to little.
I would choose to keep the default DZP.

Finally, as already suggested increase the central region and keep gate as it is.
This will also improve convergence.