Dear David, ----- Original Message ----- okay that was what I've been thinking too. I am calculating a molecular junction with Au(111) electrodes, the size of the electrode is of course crucial for the computing time.
However, if I look through the output of different Transiesta examples¹ I find that third number to be 3, or even 4.² Reading the manual and searching the internet I realized that in Transiesta this means that some part of the Hamiltonian is cut away. The consequences of this might be negligible, but strictly speaking the results are wrong in the sense that they contradict the manual. This surprised me and I was not so sure anymore if that auxiliary supercell is the right thing to look at or if I've understood the manual correctly (i.e. that the third number should be 2). As far as I've understood if you have 2 you are sure things are ok, but having 3 does not mean things are wrong. I think (again, as far as I've understood) that if you have 2 the matrix is strictly tridiagonal and certain numerical routine can be used to do the "Green functions stuff". If you have 3 the matrix is strictly not tridiagonal, but this could simply mean that you have a few 0.000001 where you are supposed to have 0.0000. If you manage to converge numercially your results this should been that the tridiagonal routines could do their job is spite of the few 0.00001. In other words, 2 is a recomendation, not a strcit requirement. Now, 4 seems a bit too much...:) Riccardo Best wishes, David ¹ e.g. http://wiki.tstutorial.dreamhosters.com/wiki/Au-BDT (there is a link to download the output files of that example) ² in this great example (mehmet_reference/step-1-electrodes/OUTPUT.fdf): http://unam.bilkent.edu.tr/mt2/transiesta/
