Thanks, your response is greatly helpful to me! I appreciate it! At 2012-06-13 20:51:19,"Jonthan R. Owens" <[email protected]> wrote: Hello,
The values for a, b, and c depend on your system. If, for example, your system is finite in the x and y direction, but infinite in the z-direction, then you will choose 1 k-point for the x- and y- directions, but (perhaps - it depends on the length) more in the z-direction. To figure out how many k-points you need, you have to do multiple runs and find the lowest number of k-points necessary to get an accurate energy value. It would also be instructive to read other published results that discuss the chosen number of k-points for calculations on systems similar to the one you're considering. TranSIESTA does not take c into account, because the boundary conditions for transport are different than they are for DFT. Specifically, you change from an infinitely periodic system in all directions, to semi-infinite electrodes in the transport direction, while the other two directions retain the same boundary conditions. The reason that changing c may change your results is because it does affect the SIESTA run - and therefore your DM, H, and S - which will then change your TranSIESTA results. Here is Monkhors and Pack's paper. Here is the TranSIESTA paper, which discusses their chosen boundary conditions. Hope this was helpful, -Jonathan On 06/13/2012 07:48 AM, 隆小江 wrote: Dear Siesta Users, I was confused about the K-point in transiesta calculation. for example: %block kgrid_Monkhorst_Pack a 0 0 0.0 0 b 0 0.0 0 0 c 0.0 %endblock kgrid_Monkhorst_Pack some articles set a=b=1, c about 20 to 30. while some others set a=b=3~6, c=1. I hear from the http://emuch.net/bbs/ that transiesta would not take c in to account, namely there would be no difference between c=1 and c=30. but I got different results when set a=b=2, c=1 and a=b=2, c=9. so I think that it might be incorrect. some other people says that the value of a, b, c should be different for the periodic systems and nonperiodic systems. I am wondering how to set them on earth. Thank you very much for your help. I look forward to your responses!
