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<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Hi Daniele
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">The SCF runs did not converge in the CP2K output file which you attached. Thus, you are feeding the L-BFGS optimiser with invalid atomic forces.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Though the L-BFGS might get stuck in that way even with valid forces, this can usually be overcome by a restart or by using BFGS if possible.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Matthias<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> cp...@googlegroups.com <...@googlegroups.com>
<b>On Behalf Of </b>Daniele Ongari<br>
<b>Sent:</b> Freitag, 22. Februar 2019 14:39<br>
<b>To:</b> cp2k <...@googlegroups.com><br>
<b>Subject:</b> [CP2K:11324] Weird "convergence" of L-BFGS CELL_OPT<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Dear CP2K mailing list,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">We experience a strange behavior of the L-BFGS optimization algorithm when dealing with cases where SCF convergence is problematic.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">After 20 minimization steps the cp2k printed the following:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">-------- Informations at step = 21 ------------<o:p></o:p></p>
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<p class="MsoNormal"> Optimization Method = LBFGS<o:p></o:p></p>
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<p class="MsoNormal"> Total Energy = -2345.6430825804<o:p></o:p></p>
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<p class="MsoNormal"> Internal Pressure [bar] = 23.9760390703<o:p></o:p></p>
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<p class="MsoNormal"> Real energy change = 0.0028283710<o:p></o:p></p>
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<p class="MsoNormal"> Decrease in energy = NO<o:p></o:p></p>
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<p class="MsoNormal"> Used time = 5864.105<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"> Convergence check :<o:p></o:p></p>
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<p class="MsoNormal"> Max. step size = 0.0000000000<o:p></o:p></p>
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<p class="MsoNormal"> Conv. limit for step size = 0.0030000000<o:p></o:p></p>
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<p class="MsoNormal"> Convergence in step size = YES<o:p></o:p></p>
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<p class="MsoNormal"> RMS step size = 0.0000000000<o:p></o:p></p>
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<p class="MsoNormal"> Conv. limit for RMS step = 0.0015000000<o:p></o:p></p>
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<p class="MsoNormal"> Convergence in RMS step = YES<o:p></o:p></p>
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<p class="MsoNormal"> Max. gradient = 0.0082916384<o:p></o:p></p>
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<p class="MsoNormal"> Conv. limit for gradients = 0.0004500000<o:p></o:p></p>
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<p class="MsoNormal"> Conv. for gradients = NO<o:p></o:p></p>
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<p class="MsoNormal"> RMS gradient = 0.0009846623<o:p></o:p></p>
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<p class="MsoNormal"> Conv. limit for RMS grad. = 0.0003000000<o:p></o:p></p>
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<p class="MsoNormal"> Conv. for gradients = NO<o:p></o:p></p>
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<p class="MsoNormal"> Pressure Deviation [bar] = -76.0239609297<o:p></o:p></p>
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<p class="MsoNormal"> Pressure Tolerance [bar] = 100.0000000000<o:p></o:p></p>
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<p class="MsoNormal"> Conv. for PRESSURE = YES<o:p></o:p></p>
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<p class="MsoNormal">---------------------------------------------------<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">--------------------------<o:p></o:p></p>
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<p class="MsoNormal">OPTIMIZATION STEP: 22<o:p></o:p></p>
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<p class="MsoNormal">--------------------------<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">***********************************************<o:p></o:p></p>
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<p class="MsoNormal">* Specific L-BFGS convergence criteria<o:p></o:p></p>
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<p class="MsoNormal">* WANTED_PROJ_GRADIENT and WANTED_REL_F_ERROR<o:p></o:p></p>
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<p class="MsoNormal">* satisfied .... run CONVERGED!<o:p></o:p></p>
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<p class="MsoNormal">***********************************************<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The two things that look strange for us are:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">1) Max. step size and RMS step size were 'artificially' set to 0.0000000000<o:p></o:p></p>
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<p class="MsoNormal">2) Not all checks are showing convergence, while L-BFGS algorithm has decided to stop.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Therefore, we would like to know if this is an expected behavior of the L-BFGS algorithm and if yes, what is the reason behind working this way?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Please see input and output files attached.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">With best regards,<o:p></o:p></p>
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<p class="MsoNormal">Daniele and Sasha<o:p></o:p></p>
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