Dear Guanping You are right in both cases. In SIESTA, the MeshCutoff does not control the basis, only the fineness of its proyection in the operations that are done in a cartesian mesh in real space. Usually, you get a fast convergence with the mesh, (I know no case non-pathological case with a mesh bigger than 1000 Ry, and usually even 400-500 is enough). Magnetism is usually sensitive, so be careful to check total convergence of both the energy and the totalspin/ mulliken charges(spins)...
Also, the finer the mesh, the bigger the DM file. There is another parameter, MeshSubDivisions, which may help you there. About the radii, it's a bit more complicate. Look at http://www.iop.org/EJ/abstract/0953-8984/16/30/008 . Regards On Wed, Mar 10, 2010 at 07:14, Guangping Zhang <[email protected]> wrote: > DEAR Lucas, > > First ,thank you for your attention to my question again.Now after several > readings ,I get some concept of the PAO.EnergyShift. > > In ideal,we use a basis set with extending to infinite, but for reality > calculation and in fact,the orbitals are zero or near zero,so for > efficiency,we set the orbitals to be zero beyond some place named rc > (orbital-confining cutoff radii).We provide the PAO.EnergyShift to determine > the value of the rc for the orbitals with first-zeta used in the basis > set,Thus ,the rc's are different for different atom species! For > multi-zeta,the second-zeta ,the third-Dear zeta orbits and so on are > determined > using PAO.SplitNorm.I.E. the second zeta of the second-zeta orbit carries > the half of the PAO.SplitNorm norm of the whole orbit,and the third carries > the one fourth of the PAO.SplitNorm of the whole orbit,the split radius is > defined accordingly.The larger PAO.EnergyShift the smaller the rc ,and the > more efficient but the less accurate! > > Am I right ?Do I understand correctly? > > But for MeshCutoff,I only know it defines the plane wave cutoff for the > grid.Then I turned to the plane wave cutoff, some book said the larger the > plane wave cutoff,the more plane waves used in the calculation and the lee > efficient but the more accurate the result!But for siesta calcilation ,the > basis set is fix at the beginning independent of the MeshCutoff. > > In your reply ,you said :'MeshCutoff controls the number of points in 3D > grid to represent, say, the charge density of your system. > The bigger the MeshCutoff the more points you have and calculation is closer > to "converged".' > > So the bigger the MeshCutoff ,the denser points we get.But it does not > affect the profile of the whole point grid,only the density! > > Am I right ? > > Respect to your kind reply! > > > > ------------------ > BEST REGARDS! > > Guangping Zhang > ----------------------------------- > Atom and Melecular Physics > Physics and Electronics College > Shandong Normal University > Shandong,Jinan,China > ------------------------------------ -- Lucas Fernández Seivane Ph. D. Candidate Universidad de Oviedo - CINN
