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QuantumATK => General Questions and Answers => Topic started by: wot19920302 on April 1, 2018, 09:15

Title: a unexpected tranmission dip at fermi level
Post by: wot19920302 on April 1, 2018, 09:15
Dear Quantumwise staffs:
            I construct a device using (4,4) carbon nanotube(CNT) as electrodes connecting to carbon atoms chains and calculate transmission spectra. (Mesh-cutoff I select is 100 hatree and k-point is 1*1*100. The functional is spindependent GGA-PBE). However,  there are sharp transmission dips at fermi level  whether bias voltages are applied nor not .  It's well kown that (4.4) CNT is metallic and there is no bandgap around fermi level.  I can't figure out why there are unexpected dips in transmission spectra, can anyone help me? :o
           Best
          P.S  Fig.1 is calculated transmission specta at 0V, and Fig.2 is contact types of device I construct.
Title: Re: a unexpected tranmission dip at fermi level
Post by: Petr Khomyakov on April 1, 2018, 10:25
Even if you have metallic electrodes, you can still have a transport gap, because the transmission spectrum is also determined by the central /scattering region that have a carbon chain with the electronic properties different from that of the electrodes.  You may have resonances, Fano resonances and so on, depending on how the energy levels of the chain are aligned with the Fermi level given by the metal electrodes, as well as on the level broadening given by the coupling to the electrodes.

I would suggest doing a literature search and reading some papers to better analyze your results.

You may also calculate the energy levels of isolated chain and/or the transmission as a function of separation distance between the chain and electrode. You should also compute more analysis objects, e.g., PLDOS across the device. 
Title: Re: a unexpected tranmission dip at fermi level
Post by: wot19920302 on April 2, 2018, 02:27
thank you for your help! ;D