You seem to think that k-points are a generic chosen value. It is not. You should think of k-points in _exactly_ the same way as in regular siesta calculations. And what does one do with k-points in siesta? Basically, you converge them...
I would highly advice you to read Kittel, Martin, or any other book on condensed matter theory where the Brillouin zone is explained! Perhaps, that would reveal the importance of choosing a correct and appropriate k-point sampling? If you have a professor, ask her/him for guidance. NOTE: http://www.rsc.org/suppdata/c5/cp/c5cp04613k/c5cp04613k1.txt the k-point samplings for transiesta and tbtrans _are_ different. REMARK: that this input fdf file is for a future release of transiesta/tbtrans. Hence not all keywords are used in the currently available transiesta/tbtrans. The k-grid is as written in the article. 5 during transiesta, 25 and 50 for tbtrans. The value 25 also exists in that file. 2016-01-19 21:38 GMT+01:00 ticu Cubot <[email protected]>: > Dear TranSiesta users, > > I am (still) confused on the k-sampling needed in the three steps (denoted > 1, 2, 3 below) in transport calculations for molecular junctions. Let me > refer to Au-BDT-Au, with all BDT atoms having y=0 (or almost zero). Is is > correct, if I (roughly) set > > 1. kx=8, ky=2, kz=50 for electrode-alone calculations to get the files > electrode.TSHS > kx and ky should be the same as chosen for your device calculation. kz should just be very high. I tend to use 100, but anything above 50 would probably suffice... (converge if in doubt...) > > 2. ky=8, ky=2, kz=2 the SR-transiesta step to obtain the SR- files > (SR.TSDE, SR.TSHS) needed for tbtrans. kx and ky same as in step 1, ky < kx > because of BDT extension along x in transverse direction. In this choice, I > was (correctly?) inspired by the k-values chosen in > Converge kx and ky. Understand what they imply by reading more material. > > http://www.rsc.org/suppdata/c5/cp/c5cp04613k/c5cp04613k1.txt > > 3. kx=16, ky=4, kz=50 for tbtrans calculations. That is, more dense > sampling for tbtrans than for transiesta (step 2), because > k_xyz-convergence of transmission is slower. Here I would note that in the > above link the same kgridMonkhorstPack seemed to have been used both in > step 2 and 3 (this is very surprising for me!); anyway, > TBTkgridMonkhorstPack is not explicitly given, and because other TBT > settings are given in that file, I assume that transiesta-k-grid and > tbtrans-k-grid were the same. > Converge kx and ky. Set kz=1. > > Many thanks for illuminating me on this point. > > ticu > -- Kind regards Nick
