Dear all, Qn 1: I have a question that when to start use ecutrho ? That is I am using USPP, that means my pseudopotential depends on both ecutwfc (majorily) and ecutrho. So, as a thumb rule ecutrho should be from 8-12 times ecutwfc. I tried both ways as follows:
Way 1: I have done optimization of ecutwfc (Ry) , with default ecutrho (not specifying ecutrho in input file), because I felt most important is ecutwfc since it works on varational principle. optimization of k-point, degauss, lattice constant all these stuffs with default ecutrho(4x ecutwfc). Completed optimization. Then with those optimised results, I also tried to find out which is better value of ecutrho, whether 8,9,10,11,12 times ecutwfc and found that 10 times is better. That is if my ecutwfc is 60 Ry , ecutrho is 600 . Now I started my scf , nscf, dos, bandstructure etc. Way 2: From first onwards, for optimization part itself I started to use also ecutrho. Then k-point, on going to lattice constant I found that, lattice constant of 10.10783(Bohr) = -429.99249320 Ry 10. 11783(Bohr) = - 429.99249304 Ry. It's very close, still I have to optimise three more atleast two more digits in lattice constant. Also I found that, default ecutrho only has the lower energy compared to this, while optimization. 10.10783(Bohr) (default ecutrho ) = -429.99268209 10.11783 (Bohr) (default ecutrho) = -429.99267906 If this would be the case, then it will be most difficult for me to compare which atomic positions are better. If I use ecutrho as 8-12 times ecutwfc. Qn: 2 , when there is any comparison or optimization , I feel using default ecutrho is better But on calculation scf, nscf dos bandstructure etc we may stick on to thumb rule 8-12 times ecutwfc = ecutrho. Is my opinion is correct or otherwise which Way of doing things are better way 1 or way 2 ? with thanks Singaravelan T R I also tried with other compound, that shows the same trend as above.
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