Hi Martin, Thanks for this information. The optical mesh in Siesta is then simply a set of k-points at which the intraband transitions for evaluating eps(w) are calculated, and its refinement allows approximating the volume integral over the Brillouin zone with a higher accuracy - am I correct?
Suppose, I calculate the properties of a solid using a 5x5x5 Optical.Mesh, then 10x10x10, then ... 60x60x100, and first I find big variations in eps(w) for between 5^3 and 10^3. Then, as Optical.Mesh becomes denser, I find that eps(w) have converged to some "steady state solution". Does this mean that the variations in eps(w) at low k-point density are due to the insufficient sampling rate and as the sampling rate increases, I have a more accurate value of the integral over the BZ? Andrey -----Original Message----- >From: Martin Blaber <[EMAIL PROTECTED]> >Sent: Jul 19, 2007 6:47 PM >To: [email protected] >Subject: Re: [SIESTA-L] Optical.Mesh > >Hi Andrey, > >For bulk materials a Monkhorst Pack grid of 21^3 is sufficient to stop >the eps(w) for a constant optical mesh (Depending on the system). >Whereas an optical mesh grid of 41^3 vs 45^3 still shifts eps(w) around >a bit for constant Monkhorst Pack grid. The broadening also affects what >can be considered converged. I generally keep the optical broadening >very low as you can always broaden more but never less. However, this >does mean an optical mesh of 45 isn't sufficient for convergence. Hope >this helped. > > >Cheers, >Marty > >--------------------- >Martin Blaber >Institute for Nanoscale Technology >Dept. of Physics and Advanced Materials >University of Technology, Sydney > > > >[EMAIL PROTECTED] wrote: > >Hi all, > >I am trying to find some description of the Optical.Mesh variable >which is more detailed than the one given in the Siesta manual. >Some of my colleagues insist that the convergence of optical properties >eps(w) with respect to the number of k-points in the integral wrt >k over the BZ has to be shown not based on the vaues in the Optical.Mesh but >rather based on the values of MonkhorstPack_grid. How can I prove the >opposite, i.e. that BZ sampling grid refinement for optical property >calculations must be based on the Optical.Mesh variable? > >Thanks, > >Andrey Semichaevsky, >CEMOS, ECE Dept., UMass Lowell ________________________________________ PeoplePC Online A better way to Internet http://www.peoplepc.com
