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<p>Hi Geng,</p>
<p>The plane wave basis depends on the size of the unit cell.
Therefore, a change of the cell dimensions corresponds to a change
of basis. If the energy difference that comes from this change of
basis is large the optimizer cannot converge. With CELL_REF you
prevent this issue by fixing the basis (which is now independent
of the volume of the simulation domain).</p>
<p>By the way, you are confusing the cell optimization and SCF: The
SCF is the energy minimization at each step of the cell
optimization (and this always converged). Only the cell
optimization did not converge.</p>
<p>Regarding the EPS_SCF: a tighter value can lower the number of
cell optimization steps, but each step will be more expensive. You
have to test it yourself.<br>
</p>
<p>Cheers,</p>
<p>Fabian<br>
</p>
<div class="moz-cite-prefix">On 27.10.2021 20:50, GENG YUAN wrote:<br>
</div>
<blockquote type="cite"
cite="mid:d4b2ad27-1cea-4e3c-97eb-f49f52fe0ebcn@googlegroups.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
Dear Fabian,
<div><br>
</div>
<div>Many thanks for your reply. I added CELL_REF in my simulation
and it works!</div>
<div><br>
</div>
<div>Is it because that CELL_REF set a larger cell dimension, so
the change of my real cell volume during the cell_opt is always
under this reference cell volume, therefore the SCF could
converge rather than keep fluctuating? (please correct me if I'm
wrong). I found some information saying that CELL_REF is to fix
the plane-wave basis whilst doing a cell_opt, but I don't know
what does this means (I will try searching more).</div>
<div><br>
</div>
<div>About the EPS_SCF, do you have any suggestions about what
criteria could I apply instead of the one I used in my
simulation (1.0E-06)?</div>
<div><br>
</div>
<div>Many thanks for your help!</div>
<div>Sincerely,</div>
<div>Geng.<br>
<br>
</div>
<div class="gmail_quote">
<div dir="auto" class="gmail_attr">在2021年10月27日星期三 UTC-4
上午3:42:53<a class="moz-txt-link-rfc2396E" href="mailto:fabia...@gmail.com"><fabia...@gmail.com></a> 写道：<br>
</div>
<blockquote class="gmail_quote" style="margin: 0 0 0 0.8ex;
border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div>
<p>Hi Geng,</p>
<p>Add a &CELL_REF section
(<a
href="https://manual.cp2k.org/cp2k-8_2-branch/CP2K_INPUT/FORCE_EVAL/SUBSYS/CELL/CELL_REF.html"
target="_blank" rel="nofollow"
data-saferedirecturl="https://www.google.com/url?hl=zh-CN&q=https://manual.cp2k.org/cp2k-8_2-branch/CP2K_INPUT/FORCE_EVAL/SUBSYS/CELL/CELL_REF.html&source=gmail&ust=1635446169936000&usg=AFQjCNH2bXPUa5kWTdo6QnQxRGiovHr09g"
moz-do-not-send="true" class="moz-txt-link-freetext">https://manual.cp2k.org/cp2k-8_2-branch/CP2K_INPUT/FORCE_EVAL/SUBSYS/CELL/CELL_REF.html</a>).
With <br>
</p>
<p>&CELL_REF<br>
ABC 10.83*1.5 10.83*1.5 7.22*1.5<br>
&END<br>
</p>
<p>the optimization converges within 35 steps. You could
decrease EPS_SCF to reduce the noise in the forces.</p>
<p>Cheers,</p>
<p>Fabian<br>
</p>
</div>
<div>
<div>On 26.10.2021 23:02, GENG YUAN wrote:<br>
</div>
</div>
<div>
<blockquote type="cite"> Dear CP2K Users,
<div><br>
</div>
<div>I am attempting to run the cell optimization for a
single bulk Cu (with 72 atoms). However, the SCF
calculation can not converge: It reached the maximum
number of optimization steps (500) and therefore exit
the optimization. <br>
<br>
</div>
<div>I also tried changing the original lattice in my
simulation (with associated coordinate) but it didn't
work either.</div>
<div><br>
</div>
<div>So far, the cell optimization only converged when I
use a smaller bulk Cu (with 32 atoms). But we'd like to
run a larger system.</div>
<div><br>
</div>
<div>I've attached my input, output, the original Cu
coordinate, as well as the trajectory during cell
optimization here for your convenience. Any ideas are
welcome! </div>
<div><br>
</div>
<div>Below is the input:</div>
<div>-----------------------------<br>
<div>&GLOBAL</div>
<div> PROJECT Cu_cellopt</div>
<div> RUN_TYPE CELL_OPT</div>
<div> PRINT_LEVEL LOW</div>
<div>&END GLOBAL</div>
<div>&FORCE_EVAL</div>
<div> METHOD QS</div>
<div> STRESS_TENSOR ANALYTICAL</div>
<div> &SUBSYS</div>
<div> &CELL</div>
<div> ABC 10.83 10.83 7.22</div>
<div> SYMMETRY TETRAGONAL</div>
<div> &END CELL</div>
<div> &TOPOLOGY</div>
<div> COORD_FILE_NAME ./Cu332.xyz</div>
<div> COORDINATE xyz</div>
<div> &END</div>
<div> &KIND Cu</div>
<div> BASIS_SET DZVP-MOLOPT-SR-GTH</div>
<div> POTENTIAL GTH-PBE-q11</div>
<div> &END KIND</div>
<div> &END SUBSYS</div>
<div> &DFT</div>
<div> BASIS_SET_FILE_NAME ./BASIS_MOLOPT</div>
<div> POTENTIAL_FILE_NAME ./GTH_POTENTIALS</div>
<div> &QS</div>
<div> EPS_DEFAULT 1.0E-12</div>
<div> &END QS</div>
<div> &MGRID</div>
<div> CUTOFF 400</div>
<div> NGRIDS 5</div>
<div> REL_CUTOFF 60</div>
<div> &END MGRID</div>
<div> &SCF</div>
<div> SCF_GUESS ATOMIC</div>
<div> EPS_SCF 1.0E-06</div>
<div> MAX_SCF 200</div>
<div> ADDED_MOS 100</div>
<div> &OUTER_SCF</div>
<div> MAX_SCF 50</div>
<div> EPS_SCF 1.0E-6</div>
<div> &END</div>
<div> &DIAGONALIZATION T</div>
<div> ALGORITHM STANDARD</div>
<div> &END DIAGONALIZATION</div>
<div> &MIXING T</div>
<div> METHOD BROYDEN_MIXING</div>
<div> ALPHA 0.1</div>
<div> NBROYDEN 8</div>
<div> &END MIXING</div>
<div> &SMEAR ON</div>
<div> METHOD FERMI_DIRAC</div>
<div> ELECTRONIC_TEMPERATURE [K] 500</div>
<div> &END SMEAR</div>
<div> &PRINT</div>
<div> &RESTART ON</div>
<div> &END RESTART</div>
<div> &END PRINT</div>
<div> &END SCF</div>
<div> &XC</div>
<div> &XC_FUNCTIONAL</div>
<div> &LIBXC</div>
<div> FUNCTIONAL XC_GGA_X_PBE_R</div>
<div> &END</div>
<div> &LIBXC</div>
<div> FUNCTIONAL XC_GGA_C_PBE</div>
<div> &END</div>
<div> &END XC_FUNCTIONAL</div>
<div> &VDW_POTENTIAL</div>
<div> POTENTIAL_TYPE PAIR_POTENTIAL</div>
<div> &PAIR_POTENTIAL</div>
<div> LONG_RANGE_CORRECTION</div>
<div> PARAMETER_FILE_NAME dftd3.dat</div>
<div> TYPE DFTD3</div>
<div> REFERENCE_FUNCTIONAL revPBE</div>
<div> &END PAIR_POTENTIAL</div>
<div> &END VDW_POTENTIAL</div>
<div> &XC_GRID</div>
<div> XC_DERIV NN50_SMOOTH</div>
<div> &END XC_GRID</div>
<div> &END XC</div>
<div> &END DFT</div>
<div>&END FORCE_EVAL</div>
<div>&MOTION</div>
<div> &CELL_OPT</div>
<div> EXTERNAL_PRESSURE 0</div>
<div> TYPE DIRECT_CELL_OPT</div>
<div> KEEP_SYMMETRY TRUE</div>
<div> MAX_DR 1.0E-05</div>
<div> MAX_FORCE 1.0E-05</div>
<div> RMS_DR 1.0E-05 </div>
<div> RMS_FORCE 1.0E-05</div>
<div> MAX_ITER 500</div>
<div> OPTIMIZER BFGS</div>
<div> &END CELL_OPT</div>
<div>&END MOTION </div>
</div>
<div>------------------------------------</div>
<div>Many thanks,</div>
<div>Geng.</div>
<div><br>
</div>
</blockquote>
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