Dear Dexi! You should not set nember of CG steps to zero - it is not necessary. You right that you should perform convergence of your property of interest, but first structural relaxation is important as I suppose - maybe not in your case, but often it is so. So select high meshcutoff about 400-500 and vary density of kpoint grid and plot how it depends on FORCES. From this plot you will select kpoints, then take this kpoints fixed and vary meshcutoff to plot dependence on forces again. It is forces, not total energy are relevant for structural relaxation. Enter in google "graphene transiesta" and 1st link will help I believe.
четверг, 24 июля 2014 г. пользователь 邵德喜 написал: > Thanks very much.The unit is Ry. > I was told that when I get the original structure ,I should do convergence > tests first,structual relaxation comes second. > In my opinion ,do convergence test without structual relaxation I should > set CG step to zero. > problem1:I check the convergency (in terms of gradually increase > Meshcutoff) of the total energy may be useless > because I was told "we should check the convergence not of the total > energy but of those properties which are relevant for our study in question > ". > But I just want to study the current-voltage relation ,it's expensive for > me to check the convergence of its transport property. > So I check the convergence of total energy instead opportunisticly. > The input.fdf file is as follows. > Thans for your replay. > Dexi Shao > > > 2014-07-24 18:22 GMT+08:00 Kanhao Xue <xuekan...@gmail.com > <javascript:_e(%7B%7D,'cvml','xuekan...@gmail.com');>>: > >> Dear Dexi, >> >> I wonder what is the unit of your Mesh cutoff? Is it in Ry? >> >> Siesta is using atomic orbital as the basis, which is quite different >> from plane-wave based codes like VASP. In plane-wave code, the plane wave >> cutoff energy directly determines your basis, and thus influences the >> result a lot. >> >> In Siesta we have the mesh cutoff concept. A large cutoff is required for >> accurate result. Usually for LDA, 250 Ry is sufficient and for GGA 350 Ry >> is sufficient. >> >> In my opinion you do not need to go up to 600 Ry to check. >> >> However, indeed your energy changes too much with Mesh cutoff. Can you >> upload your input fdf file for more information? >> >> Kanhao >> >> >> On Thu, Jul 24, 2014 at 11:43 AM, 邵德喜 <dxshao...@gmail.com >> <javascript:_e(%7B%7D,'cvml','dxshao...@gmail.com');>> wrote: >> >>> Dear everyone: >>> I have done the convergence test when I check the convergency (in terms >>> of gradually increase Meshcutoff) of the total energy, I found that the >>> Total energy rise up when I increase the parameter of Meshcutoff (please >>> refer to the accesory) .Is it reasonable? >>> Ahy replay will be appreciated. >>> Dexi Shao >>> >> >> >> >> -- >> >> Sincerely yours, >> Kanhao Xue >> >> Laboratoire de Réactivité et Chimie des Solides (LRCS) >> UMR CNRS 7314 >> Université de Picardie Jules Verne >> 33 Rue Saint Leu, 80039 Amiens Cedex, France >> > > -- Best wishes, Maxim Arsent'ev, D.Sc.(Chemistry) Laboratory of research of nanostructures Institute of Silicate Chemistry of RAS
