[Pw_forum] How to achieve the convergence of Ecutrho?
Dear all, I've asked sevral people about the convergence criteria of Ecutrho test. They point out that the convergence will be achieved when the difference between two adjacent scf calculation is smaller than 0.1 meV. However, they are not very sure about the step length. From my view, the step length may pose huge effects on our calculation. Consider the cases of step lengths are 100 Ry and 0.1Ry respectively, the latter will be convergent immediately while the former will not be so fast. For the resons above, I'm really confused now. And could any nice guy show me the strict judgement of the convergence for Ecutrho? Thank you very much! Yours, Plato Tao -- --- PH.D. candidate Peng Tao Magnetism and Magnetic Materials Division National Laboratory for Material Science Institute of Metal Research, Chinese Academy of Sciences Phone +86-024-83978751 ---
[Pw_forum] How to achieve the convergence of Ecutrho?
>Dear all, > >I've asked sevral people about the convergence criteria of Ecutrho test. They point out that the convergence will be achieved when the difference between two adjacent scf calculation is smaller than 0.1 meV. However, they are not very sure about the step length. From my view, the step length may pose huge effects on our calculation. Consider the cases of step lengths are 100 Ry and 0.1Ry respectively, the latter will be convergent immediately while the former will not be so fast. >For the resons above, I'm really confused now. And could any nice guy show me the strict judgement of the convergence for Ecutrho? Thank you very much! The convergence of Ecutrho comes from the balance of time and accuracy, so the judgment is based on your own system and there is no universal one. Typically, 1Ry~10Ry should be step length under most circumstance, as one can reach the convergence reasonably fast while the additional time cost from the more than enough Ecutrho will be in the same order of magnitude as 10%, an acceptable value. Wu Feng, Chemistry and Molecular Engineering, Peking University
[Pw_forum] How to achieve the convergence of Ecutrho?
Dear Plato Tao, as for any convergence parameter, the criterion is analogue to the epsilon-delta definition in calculus. Namely, if Q is the quantity you want to have converged (say, the total energy) within an accuracy \epsilon (the value of \epsilon depending on your own needs), with respect to a convergence parameter x (say, the cutoff): if |Q(\infty) - Q(x)| < \epsilon for all x >= x', then x' is the value of the parameter ensuring you convergence. Notice that this does not imply anything about how fast you reach convergence, so a criterion only based on differences between consecutive steps (x,x+dx,x+2dx...) is ill defined as it depends on dx. You have to estimate the value of Q(\infty), e.g. by extrapolation to large values of x, and see when your error with respect to this virtually exact result is lower than the accuracy you want to achieve. Best wishes, Guido Il 12/13/2011 08:43 AM, ?? ha scritto: > Dear all, > > I've asked sevral people about the convergence criteria of Ecutrho test. They > point out that the convergence will be achieved when the difference between > two adjacent scf calculation is smaller than 0.1 meV. However, they are not > very sure about the step length. From my view, the step length may pose huge > effects on our calculation. Consider the cases of step lengths are 100 Ry and > 0.1Ry respectively, the latter will be convergent immediately while the > former will not be so fast. > > For the resons above, I'm really confused now. And could any nice guy show me > the strict judgement of the convergence for Ecutrho? Thank you very much! > > Yours, > Plato Tao > > -- > --- > PH.D. candidate Peng Tao > Magnetism and Magnetic Materials Division > National Laboratory for Material Science > Institute of Metal Research, Chinese Academy of Sciences > Phone +86-024-83978751 > --- > > > > > ___ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -- Guido Fratesi Dipartimento di Scienza dei Materiali Universita` degli Studi di Milano-Bicocca via Cozzi 53, 20125 Milano, Italy
[Pw_forum] How to achieve the convergence of Ecutrho?
Actually, the standard of convergency for cut-off energy is not how much dE the system gained, but whether dE/dCut is near to 0 enough. Definitely, such a threahold, for dE/dCut, is also determined by yourself. The example from you was too extreme. Thinking about 100Ry as step, your result are too rough to hold the slope information. But when 10^(-5)Ry was using, even though it should give the very fine dE/dCut information as well, the results may be not good due to the accuracy of DFT, numerical methods, and computer limitation ( please consider the length of float and double float variable ). P.S.: Therefore, I think such question is not the one of sci. & tech. rather than your thinking method. This may be the reason that no person reply such a post in emuch. -- GAO Zhe CMC Lab, Materials Science & Engineering Department, Seoul National University, South Korea At 2011-12-13 15:43:04,"??" wrote: >Dear all, > >I've asked sevral people about the convergence criteria of Ecutrho test. They >point out that the convergence will be achieved when the difference between >two adjacent scf calculation is smaller than 0.1 meV. However, they are not >very sure about the step length. From my view, the step length may pose huge >effects on our calculation. Consider the cases of step lengths are 100 Ry and >0.1Ry respectively, the latter will be convergent immediately while the >former will not be so fast. > >For the resons above, I'm really confused now. And could any nice guy show me >the strict judgement of the convergence for Ecutrho? Thank you very much! > >Yours, >Plato Tao > >-- >--- >PH.D. candidate Peng Tao >Magnetism and Magnetic Materials Division >National Laboratory for Material Science >Institute of Metal Research, Chinese Academy of Sciences >Phone +86-024-83978751 >--- > > > > >___ >Pw_forum mailing list >Pw_forum at pwscf.org >http://www.democritos.it/mailman/listinfo/pw_forum -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20111213/07d5406c/attachment.htm
[Pw_forum] el_phon
Dear Users! I want to modify the phonon code in /PH to obtain the electron-phonon matrix elements. I want to write it out in a file. If I good understand, the matrix elements are stored in the elph.f90 file (in the module el_phon). Is not it? -- Demj?n Tam?s -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20111213/bf95976f/attachment.htm
[Pw_forum] software to draw phonon spectra for windows
Dear all, Could anyone please suggest me some free software to draw phonon spectra under windows XP systems? Great thanks! Best regards, Liwei -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20111213/c10e93eb/attachment.htm
