Dear SIESTA Users, I have a few conceptual questions about TranSIESTA and would be really grateful if you help me with them. In fact, the answer to these questions is quite important for my calculations. I have used TranSIESTA to study the current in an 8-AGNR system. My system consists of 16X7=112 carbon atoms. 16 atoms make the left electrode, 5X16=80 atoms make the scattering region, and 16 atoms make the right electrode. As the transport direction is along the z direction, my system would look like this along the z direction:
... + Left 16 atoms + Scat. region 80 atoms + Right 16 atoms + Left 16 atoms + Scat. region 80 atoms + Right 16 atoms + ... I successfully calculated the current in this case for a particular bias. Then, I increased the length of the vector along the z direction by about 3 Angs and repeated the calculation. Note that I only increased the length of the vector and did not add any atoms. All the other settings in the .fdf file was kept intact. In this case, my system looked like the following: ... + Vacuum of about 3 Angs + Left 16 atoms + Scat. region 80 atoms + Right 16 atoms + Vacuum of about 3 Angs + Left 16 atoms + Scat. region 80 atoms + Right 16 atoms + ... Interestingly, I found almost identical current values as the ones obtained in the case with no vacuum. Finally, I increased the void to 10 Angs without modifying any other settings. In this case, although the DM did not converged in 1000 iterations, the code calculated currents similar to the ones obtained for no vacuum but with about 40 percent deviation. My questions are the following: 1- Does the neighboring scattering regions affect each other in the scattering region calculation? What is the difference between calculations which do not include any vacuum with calculations which consider, say a 10 Angs, vacuum? 2- How should I make the code converge when I increase the void to 10 Angs? How should I modify my .fdf code in the case with vacuum so that I can obtain identical currents to the case with no vacuum. Sorry for my bother-making. I am trying to simulate a system with TranSIESTA which contains quite different left and right electrodes that cannot come into direct contact without the scattering region in between. The only way for me is to introduce vacuum between neighboring scattering regions. In brief, I would be really grateful if you tell me how can I determine the size of the sufficient vacuum between neighboring scattering regions so that my results can be credible. Best wishes, Mohammad,
