Hi Mohsen,
the smearing technique is meant to be a numerical tool to perform the thermodynamic limit (# of kpts going to infinity, i.e. size of the system going from being finite to extended). The actual value of the smearing parameters thus depends on how far the evaluation of the limit is, i.e. on how many kpts you are using in the calculation. Generally, the bigger the # of kpts, the smaller the smearing can be. The smaller the smearing, the higher the accuracy of the final limit. But smearings that are too small (relative to the # of kpts) lead to unphysical features, especially in the spectra (due to the finiteness of the systems studied)... After all, the value of the smearing (and the number of kpts) depend on the accuracy you want to reach. (if you want eg to describe the 1/sqrt(E) divergences of a nanotube DOS and JDOS you probably need a lot of kpts). A rule of thumb to avoid spurious features is the following: given a finite mesh of kpts, the bands of the systems are discretized. The smearing parameter should be of the order of the difference in the eigenvalues (transition energies in your case) corresponding to nearby kpts (i.e., the smearing should be of the order of the discretization induced on the eigenvalues, or transition energies in the case of epsilon.x) practically, I would start with the default value of the smearing, and then check a posteriori. hope it helps Andrea > Dear Andrea, > Thanks for your answer, I know the meaning of these parameters, > I want to know how can i determine these parameters for a system > (Like a CNT (6,0))? > Thanks for your answers. > Mohsen > > On Mon, May 17, 2010 at 7:37 PM, Andrea Ferretti <ferretti at mit.edu> wrote: > > > Dear Mohsen, > > the meaning of these parameters (smearing for inter and intra band > transitions) is somehow explained in the epsilon.x manual, > ~espresso/Doc/eps_man.pdf > > Andrea > > > > Dear all, > > I have not any answer for this question, Actually I have a problem > > about eps.x, I can't understand this two parameters (intersmear, > > intrasmear). > > How can i determine (intersmear, intrasmear). > > Thanks for your answers > > _______________________________________________ > > Pw_forum mailing list > > Pw_forum at pwscf.org > > http://www.democritos.it/mailman/listinfo/pw_forum > > > > -- > Andrea Ferretti > Oxford University, Department of Materials > Parks Road, Oxford OX1 3PH, UK > Tel: +44 (0)1865 612796; ?Skype: andrea_ferretti > URL: http://quasiamore.mit.edu > > Please, if possible, don't send me MS Word or PowerPoint attachments > Why? See: ?http://www.gnu.org/philosophy/no-word-attachments.html > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > > > > -- Andrea Ferretti Oxford University, Department of Materials Parks Road, Oxford OX1 3PH, UK Tel: +44 (0)1865 612796; Skype: andrea_ferretti URL: http://quasiamore.mit.edu Please, if possible, don't send me MS Word or PowerPoint attachments Why? See: http://www.gnu.org/philosophy/no-word-attachments.html