Dear staffs:
I want to construct a Armchair MoS2 nanoribbon device descrided in the paper
Anisotropic thermoelectric
behavior in armchair and zigzag mono- and fewlayer MoS2 in thermoelectric generator applications(149 atoms supercell as central region)to study some properties, here are my processes:
1. unit cell optimization
1). Click "Add>Add from Database" and locate molybdenite. Add it to the stash
2). Use the mouse to select and delete the 3 atoms to the right in the cell. This leaves a single layer of MoS2
3).Now the vector C is too long so I assume that the C direction is non-periodic, as the result , expand vacuum along the C direction , and center the unit cell using coordinate tools(fig.1)
4).Optimize the modified unit cell with DFT(GGA, k-points 3*3*1, mesh cut-off of 75 Ha,force and stress of 0.05 and 0.05 eV , respectively. Uncheck Constrain cell A,B,leave C checked) (fig.2), perform optimization and then get optimized unit cell
5).Adjust supercell parameters to get orthogonal cell,swap axis(make the C direction transport dierection)(fig.3), repeat unit cells along B(5 times) and C(5 times) to get the central region(149 atoms supercell as central region), then click “device from bulk"
2.setting parameters
After studying
http://docs.quantumwise.com/tutorials/thermoelectrics_cnt_isotope.html . I began to set parameters to get Transmission Spetrum and phonon Transmission Spetrum.
1)Click “New calculation” with DFT(LDA 、k-pionts 1*1*100、density mesh cut-off of 10 Ha), particularly, electron temperature in calculator setting is not “real temperature” and electronic transmission spectrum is insensitive to electron temperature so it doesn’t matter the value is 300K ,500K or 800K.
2)Click “Transmission spectrum”, set the energy range to -2 to 2eV. k-pionts 1*1*100. the number of points 201.
3)Click ”New calculation” with Stillinger-Weber potential
4)Click”Dynamic marix” repetition is custom and na、nb: 1*1
5)Click”phonon transmission spectrum”, set energy range from 0 to 0.5eV and q-pionts 1*1,the number of points 201
3. data analyzing
After calculating, I get one transmission_spectrum.nc and one phonon_transmission_spectrum.nc. Then I can use
thermoelectric coefficient plugins to calculate conductance, Seebeck’s coefficient, electronic contribution to thermal conductance, and phonon contribution to thermal conductance at different temperatures by changing values of “electrode temperature” in
thermoelectric coefficient plugins. in addition, I think that "electrode temperature” in
thermoelectric coefficient plugins. affect thermoelectric coefficient by Fermi disribution and Boltzmann distribution.
These are my thoughts and what I have done, but the results disappoint me. I will appreciate your kindness if you could point out my mistakes and guide me.
Best regards.
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! I konw the calculation of dynamical matrix with DFT is much time-consuming, but the clusters have been calculating electron transimission spectrum and phonon transmission spectrum of a MoS2 nanoribbon device( shown below) with DFT for 24 hours, is that normal?
