QuantumATK Forum
QuantumATK => General Questions and Answers => Topic started by: marmotte on November 7, 2012, 13:41
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Dear ATK team,
Could you please help me in the calculation of the thermolectric prop. of the attached bulk material. I'm wondering if I need to swaps its axis. I taught that I have to calculate the transmission spectrum but with the present structure, I can't select the "transmission spectrum" in the Analysis section.
Thank you in advance for your help,
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The rule is that the cell needs to be oriented like an electrode. Thus, the easiest way is to cleave the crystal and use the "Electrode" setting on the 3rd page of the cleave tool (i.e. the default). You may want to repeat it in C, say 2 times, to make sure all matrix elements are accounted for.
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Hi Anders, thank you for your reply.
Is this rule available for bulk in general ? even they have their cell oriented in C ?
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Yes, it doesn't matter how you obtain the cell, you can cleave it or just make a supercell and swap the axes. So the real rule is that the C axis should be parallel to Z (and the transmission is computer in this direction), and the A/B vectors should lie in the X/Y plane.
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Oh, another thing. You should remove the "from ATK.KohnSham" import in your script. It applies to an ancient version of ATK. For now VNL is tolerant to it, but it should not be used.
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Ok for this.
I have one more question. If I want to get the thermoelectric prop. versus temperature. I need to perform DFT calculation for the needed temperature and then run the thermoelectric prop. script for each temperature ?
Best
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As a first approximation it is probably sufficient to do the DFT at one temperature, since the temperature in the calculation only determines the broadening of the Fermi level, to make it easier to compute the band structure. However, in principle DFT is a zero-temperature theory as long as we don't included phonons. The post-processing script then populates the excited levels according to the finite-temperature Fermi distribution. It may of course be that a finite electron temperature changes the electronic structure; I would not assume this effect to be very strong, but you want to be really sure you need to test the assumption, of course.