Hii, Just to add some data to my previous post: The difference in scf energy (in Ry) for my system having 36 atoms is:
ecut vs energy 30 -1.42256 40 -0.0765211 45 -0.00623776 50 -0.00420366 60 -0.00482638 65 -0.00095532 So if I divide energy wrt 45ecut by 36 (number of atoms), it comes out: -0.0001732 Ry or -0.002356487 eV/atom For 50 and 60 ecut this difference becomes ~0.00017 Ry or ~0.0016 eV/atom. For the ecut (the difference between ecut 60 and 65) the difference is: -0.000026 Ry/atom or 0.00036eV/atom. What value of ecut is the perfect choice for my case: 45 or 50 or 60? I just doing vc relaxation with free xyz. Kind regards Bhamu On Sat, May 5, 2018 at 11:12 PM, Dr. K. C. Bhamu <kcbham...@gmail.com> wrote: > Dear QE Users, > > For simple compounds (binary or ternary), I know the said parameters may > be fixed tight (etot_conv_thr, 1e-5, and forc_conv_thr, 1e-5 and > conv_thr. 1d-07 or 1d-08 or 1d-09). But for complex systems, if we set them > high then it would cost much wall time. > > To avoid this, Is there any thumb rule to decide the above parameters to > be kept fix for complex bulk structures (having a combination of organic > and inorganic elements), i.e. as the number of atoms increases in the > system the above parameters can be lowered? > As far as I know, these parameters have much importance if we see per > atom. So, if we increase the number of atoms the parameters can be lowered > (Ex. for hybrid perovskites with 36 atoms in a unit cell, etot_conv_thr, > 1e-3, and forc_conv_thr, 1e-3 and conv_thr. 1d-06 ), is it? > > > Any comment will be helpful to improve my understanding or in correcting > me if I am wrong, also will save computational cost. > > > Thanks and regards, > > > Dr. K. C. Bhamu > National Postdoctoral Fellow, > Physical and Materials Chemistry Division > CSIR-NCL, Pune > Mob. No. +91-9975238952 >
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