<div>Dear Marcella,</div><div><br></div><div>Thank you for your help. We have tested the diagonalization + smearing on the O2 molecule and indeed the total spin was free to change. We then ran these settings for our graphene+Fe system and we had unexpected results. Whatever multiplicity we start from (1, 3, 7...) the total spin converged to 0 and also the integrated total spin was close to zero. However, using OT and restricting the multiplicities for each simulation, we find a more stable configuration for the triplet instead of the singlet (-1017.356 Ha versus -1017.345 Ha). In OT we also found non-zero spin density on our Iron atom (0.5) even in the singlet case, while for the diagonalization + smearing we find no spin moment on all atoms. Although our OT results do not include electronic smearing, they seem to agree with other calculations done with VASP. Do you think these qualitatively fairly different results are to be expected and do you have an advice on which ones to trust more?</div><div><br></div><div>PS: There is a significant difference in energies between OT and DIAG + smearing ( -1017.345 to -1017.315 ). We assume it is due to the smearing and not beacuse OT finds a more stable configuration. Could you confirm this is true?<br></div><div><br></div><div>PPS : For each step when starting from a triplet, we still got different number of electrons in each channel although the total spin was 0 in the end (Mulliken population analysis), is this a printing error simply?<br><div>Spin 1<br>│</div><div>│ Number of electrons: 1123<br>│ Number of occupied orbitals: 1124<br>│ Number of molecular orbitals: 2123<br>│<br>│ Spin 2<br>│<br>│ Number of electrons: 1121<br>│ Number of occupied orbitals: 1124<br>│ Number of molecular orbitals: 2121<br>│<br>│ Number of orbital functions: 6651<br>│ Number of independent orbital functions: 6651</div><div><br></div><div>Regards,</div><div>Max and Laura<br></div></div><div class="gmail_quote"><div dir="auto" class="gmail_attr">Marcella Iannuzzi schrieb am Freitag, 8. Juli 2022 um 16:45:22 UTC+2:<br/></div><blockquote class="gmail_quote" style="margin: 0 0 0 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Dear Laura<div><br></div><div>When using diagonalization+smearing the multiplicity is never fixed by default. Are you sure that you are fixing the multiplicity?</div><div>The relax_multiplicity makes no sense in this case and probably it is only creating discontinuous changes in the electronic distribution, which prevent the convergence.</div><div>Spin polarised systems are notoriously harder to converge.</div><div>Often the initial guess has a significant influence on the final result.</div><div>In general using mixing it is normal to see lower values in energy along the iterative loop, because the densities used to calculate the hamiltonian are not single solutions of the diagonalization algorithm.</div><div>0.40E+00 for alpha is very large, in particular if there are convergence issues<br></div><div><br></div><div>Regards</div><div>Marcella</div><div><br><br></div><div class="gmail_quote"><div dir="auto" class="gmail_attr">On Friday, July 8, 2022 at 1:37:36 PM UTC+2 Laura Scalfi wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Dear Cp2k forum,
<p>We are trying to run
a graphene sheet with a Fe defect (containing 1 Fe atom and 4 N
atoms, 155 atoms in total), using spin polarized Kohn-Sham (UKS). We
managed to run fixed multiplicities of 1, 3 and 5 using the keywords
UKS and MULTIPLICITY and the orbital transformation algorithm.
However, we would like to let the multiplicity relax using
RELAX_MULTIPLICITY keyword and we haven’t been able to make any
energy calculation converge yet.
</p>
<p>We are using
DIAGONALIZATION instead of OT, with ADDED_MOS 500 and a Fermi-Dirac
smearing with temperature 300 K. As of now we succeded to get
convergence for DIAGONALIZATION – using the standard algorithm –
(I) without UKS, (II) with UKS and a fixed MULTIPLICITY of 1, and
(III) with UKS and RELAX_MULTIPLICITY starting from a multiplicity of
1 (but, however large the RELAX_MULTIPLICITY, we did not observe any
switching of spin).</p>
<p>Note that, even for
the multiplicity 1, the SCF loop converges on a value higher than one
found earlier in the loop (see below), and we therefore are not sure whether we
can trust this.</p>
<p>###############################################<br>
</p>
<p> SCF WAVEFUNCTION
OPTIMIZATION</p>
<p><br>
</p>
<p> Step Update
method Time Convergence Total energy Change</p>
<p>
------------------------------------------------------------------------------</p>
<p> 1 NoMix/Diag.
0.40E+00 1.0 0.94554597 -1011.7340994699 -1.01E+03</p>
<p> 2 Broy./Diag.
0.40E+00 1.5 0.98949973 -984.4304450815 2.73E+01</p>
<p> 3 Broy./Diag.
0.40E+00 1.5 1.00114938 -1018.8335907387 -3.44E+01</p>
<p> 4 Broy./Diag.
0.40E+00 1.5 0.75169399 -1001.3444674373 1.75E+01</p>
<p> 5 Broy./Diag.
0.40E+00 1.5 0.71210144 -1019.8272742272 -1.85E+01</p>
<p> 6 Broy./Diag.
0.40E+00 1.4 0.91325270 -1013.4277794778 6.40E+00</p>
<p> <b>7
Broy./Diag. 0.40E+00 1.4 0.50466440 -1029.6824961219
-1.63E+01</b></p>
<p> 8 Broy./Diag.
0.40E+00 1.5 0.33674220 -1021.0650257790 8.62E+00</p>
<p>...</p>
<p> 40 Broy./Diag.
0.40E+00 1.4 0.00002151 -1017.3149228922 1.08E-04</p>
<p> 41 Broy./Diag.
0.40E+00 1.4 0.00001546 -1017.3151997206 -2.77E-04</p>
<p> <b>42
Broy./Diag. 0.40E+00 1.4 0.00000072 -1017.3150173627
1.82E-04</b></p>
<p><br>
</p>
<p> *** SCF run
converged in 42 steps ***</p>
<p>########################################################<br>
</p>
<p><br>
</p>
<p>The fixed
multiplicity of 3 is very hard to converge (we only managed with
specific parameters of Broyden mixing, after 500 iteration steps, and
the total spin moment (Mulliken population analysis) was not
consistent with the given multiplicity). The RELAX_MULTIPLICITY case,
starting from multiplicity 3 or 11, never converges (we set it to 1e-5,
but different values up to 0.5 don’t change anything).</p>
<p>We tried Pulay
mixing but we got an error of bad conditioning, and Direct_p_mixing seems to worsen the convergence. We also tried using
the method OT instead of STANDARD, with CG minimizer or DIIS (as done in a test case with O2), and in
all cases it never converged and the OT eigensolver never converged
at each step.
</p>
<p>Does anyone can
suggest other parameters/methods to use or point out if there is a
mistake in our simulations? We attach here a typical input file.<br></p>
<p>Thank you very much,</p>
<p>Sincerely,</p>
<p>Laura</p>
</blockquote></div></blockquote></div>
<p></p>
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