Dear Frank, Many thanks for your explanation. -Zara On Thu, Nov 24, 2016 at 1:57 PM, Frank Maier <[email protected]> wrote:
> You don't have to take more than 1 k-point in z direction. I got also > confused by these examples. > A more detailed explanation can be found in > departments.icmab.es/leem/siesta/tlv14/slides13.pdf > page 5 and 17. > > You have to use a high number of k-points in transport direction for the > electrodes, 1 k-point in transport direction for the device and also > TBTrans, because of the open boundary condition. > In the transverse direction however, you have to use the converged k-point > from the siesta runs in the electrode and device, and a much higher number > in the TBTrans run. > > Best wishes, > Frank > On 11/12/2016 05:03 PM, Zara Nosh wrote: > > Dear Dr. Thomas Archer > Thank you very much for your reply. > > I completely agree with you, but in all transiesta examples > <http://dipc.ehu.es/frederiksen/tstutorial/index.php/Exercises_TS_School_2009>, > They have taken high k-point in transport direction for device and also > tbtran run. > As we have open boundary condition in z direction, I can't understand why > we should take more than 1 k-point in z direction. > > Any comments are appreciate. > Best > Zara > > On Sun, Nov 6, 2016 at 9:32 PM, Thomas Archer <[email protected]> wrote: > >> I have little knowledge of trans siesta but I work on smeagol, the >> methodology should be the same. >> >> >> >> K points are a little different than standard DFT, we typically use >> several steps so avoid a massive self consistent cycle with a dense K-point >> grid. >> >> >> electrodes: These are constructed periodic along z so should be >> constructed with k-points in the z direction. You want to get the >> electrodes as accurate as possible since this is one of the least expensive >> parts of the calculation you should use lots of K-points along z. The xy >> plane should be dense enough to give the correct electronic structure >> similar to a standard DFT calculation. (e.g.4x4x100) >> >> >> SCF of the junction: Since you break the symmetry along Z when you >> construct the junction it makes no sense to use more than 1 k-point along >> z. In the xy plane use a normal number of k-points (for siesta) and >> this should be kept consistent for the electrodes and the junction. >> (e.g.4x4x1) >> >> >> >> Transmission: Here the xy plane you should have a very dense grid as the >> transmission is very k-dependant, but typically does not need to be done >> self consistently. (e.g. 100x100,1) >> >> >> Tom Archer >> >> >> >> ------------------------------ >> *From:* [email protected] <[email protected]> on behalf of >> Zara Nosh <[email protected]> >> *Sent:* Sunday, November 6, 2016 5:20:35 PM >> *To:* [email protected] >> *Subject:* [SIESTA-L] k-point sampling in transiesta >> >> Dear all, >> For transiesta calculations, we have to use high k-point in the transport >> direction (z) to simulate the semi-infinite electrodes. >> >> Do we need high kz, just for electrodes' calculations? or for both >> electrodes and device? >> >> Can we use normal kz (like usual siesta calculations) for device part? >> For example if our system is large in z direction, about 60 Ang, can we use >> just 1 k point for kz? >> >> I really appreciate your help in advance. >> With best regards, >> -Zara >> Tern uni >> > > >
