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QuantumATK => General Questions and Answers => Topic started by: bfazi on July 10, 2015, 12:23

Title: band gap temperature dependence
Post by: bfazi on July 10, 2015, 12:23

Hello there

I calculated the silicene nanoribbon band gap in two different temperatures (300K and 4K). The results were amazing! For 300K the structure had 0.25eV band gap but for 4K the structure had no band gap! Why?

Title: Re: band gap temperature dependence
Post by: zh on July 10, 2015, 13:58

Which kind of temperature are you talking about? If  it is the electron temperature defined in the Fermi-Dirac distribution for the determination of electron occupation, something (parameters setup or calculation step) must be wrong in your calculations.  So you had better  post your input file.

Title: Re: band gap temperature dependence
Post by: Dipankar Saha on July 11, 2015, 12:38

Where did you find the band-gap?  In, DFT .....while we obtain any ground-state property...essentially it's at 0 K !!!

[Now, you can further include any semi-empirical relation....and plug this E_g (0 K) there.....to obtain some temp. dependency... But I guess that's not the story here...]

In your case.... you varied the right-left electrode temperatures... / Ideally these electrodes, are carrier reservoirs ....thus as per the bias one is your source and other is the sink..../ Here, essentially you varied the injected carriers.....; and obtained the transmission....
Gap around the energy-zero in the transmission spectrum...may or may not reflect the actual band-gap...!!!

Regards__
Dipankar

Title: Re: band gap temperature dependence
Post by: zh on July 11, 2015, 12:48

You had better check the band gap of the bulk system (rather than the device configuration) of  silicene nanoribbon at two different electron temperatures.

Title: Re: band gap temperature dependence
Post by: Jess Wellendorff on July 20, 2015, 13:38

Perhaps an electron temperature of 4000 eV is just high enough to smear out the electron distribution around the Fermi level and thereby close the energy gap. 4000 eV times the Boltzmann constant is roughly 0.35 eV...