Dear all, I have observed a rather curious behaviour when performing convergence testing for CuSO4 x 5H2O. For the convergence testing I have displaced the oxygens surrounding the Cu and S atom by 10% of the equilibrium Cu-O and S-O bond lengths and computed the forces on each of the atoms for various k-point grids, smearing widths (marzari-vanderbilt type), ecutrho and ecutwfc. To my surprise I found that the ecutrho value did not converge up to a dual parameter of 5 (i.e., wfc cut = 50 Ry and ecutrho = 1000 Ry; forces vs dual parameter plots available on google drive: https://drive.google.com/drive/folders/1YaotezLaEHiSKouW19azGMdC6T8J-Jg8?usp=sharing). I am using ultrasoft PP from the GBRV library, usually I find that a dual parameter of 2 or 3 (i.e., ecutrho 8 or 12 times larger than ecutwfc) yields well converged forces. My question now is if there is any reason, why I should NOT use such a high dual parameter for the geometry optimization?
All the best and many thanks, Johannes Johannes Meusburger ISIS Neutron and Muon Source, UK This email and any attachments are intended solely for the use of the named recipients. If you are not the intended recipient you must not use, disclose, copy or distribute this email or any of its attachments and should notify the sender immediately and delete this email from your system. UK Research and Innovation (UKRI) has taken every reasonable precaution to minimise risk of this email or any attachments containing viruses or malware but the recipient should carry out its own virus and malware checks before opening the attachments. UKRI does not accept any liability for any losses or damages which the recipient may sustain due to presence of any viruses.
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