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<span lang="EN-US" style="mso-ansi-language:EN-US">Dear all,<o:p> </o:p></span></p>
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<span lang="EN-US" style="mso-ansi-language:EN-US">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:
<a href="https://drive.google.com/drive/folders/1YaotezLaEHiSKouW19azGMdC6T8J-Jg8?usp=sharing">
https://drive.google.com/drive/folders/1YaotezLaEHiSKouW19azGMdC6T8J-Jg8?usp=sharing</a>).<o:p> </o:p></span></p>
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<span lang="EN-US" style="mso-ansi-language:EN-US"><span style="mso-spacerun:yes"> </span>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?<o:p> </o:p></span></p>
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<span lang="EN-US" style="mso-ansi-language:EN-US"><o:p> </o:p></span></p>
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<span lang="EN-US" style="mso-ansi-language:EN-US">All the best and many thanks,<o:p> </o:p></span></p>
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<span lang="EN-US" style="mso-ansi-language:EN-US"><o:p> </o:p></span></p>
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<span lang="EN-US" style="mso-ansi-language:EN-US">Johannes<o:p> </o:p></span></p>
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<span lang="EN-US" style="mso-ansi-language:EN-US"><o:p> </o:p></span></p>
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<span lang="EN-US" style="mso-ansi-language:EN-US">Johannes Meusburger <o:p> </o:p></span></p>
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<span lang="EN-US" style="mso-ansi-language:EN-US">ISIS Neutron and Muon Source, UK<o:p> </o:p></span></p>
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<span lang="EN-US" style="mso-ansi-language:EN-US"><o:p> </o:p></span></p>
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