[CP2K-user] [CP2K:21461] Regarding the problem of using three functionals to optimize the spatial structure of the high spin state of the spin crossover material [Fe(pz)][Ni(CN)4]
Daniel Lee
danielleelore at gmail.com
Tue May 13 02:14:44 UTC 2025
Hi, greetings:
I hope to use CP2K to optimize the spatial structure of the high spin state
of the spin crossover periodic crystal [Fe(pyrazine)][Ni(CN)4] (a MOF type
material, the crystal structure is shown in Figure 1
<https://imgur.com/a/2xhQjKi>).
This material is in a low spin state at normal pressure and low
temperature, which is a diamagnetic state. The d-layer electronic
configuration of Fe(ii) is t2g6, spin is 0, and Ni spin is 0. It will
automatically transform into a high spin state at normal pressure and 300K,
which is a paramagnetic state, the d-layer electronic configuration of
Fe(ii) becomes t2g4eg2, spin is 2, and Ni spin is 0; the difference between
the high and low spin states in the spatial structure is mainly reflected
in the different bond lengths of the Fe-N octahedron (high---2.1+A,
low---1.9+A), and the bond lengths of other chemical bonds remain basically
unchanged. The unit cell of this material has 20 atoms.
There are several studies in the field of spin crossover research (such as
a recent one DOI: 10.1063/5.0157187) showing that tpssh, b3lyp and m06l are
three functionals that are fairly good at describing the properties of spin
crossover materials, so I would like to use these three functionals to
optimize the spatial structure of the high and low spin states of
[Fe(pyrazine)][Ni(CN)4] and compare the simulation results of different
functionals.
Recently, a study (10.1021/acs.jpcc.2c01030) used quantum espresso to
simulate the PBE+D2 calculation of a similar material
[Fe(pyrazine)][Pt(CN)4]. Therefore, I used the method of this study to
optimize the spatial structure of the high and low spin states of
[Fe(pyrazine)][Ni(CN)4] using QE's PBE+D2. After setting different spin
polarization parameters for the input files corresponding to the high and
low spin state according to the experimental data (see attachment 1 for the
high spin input file and attachment 2 for the low spin input file), the
vc-relax calculations converged successfully, and the results also
reflected the spatial structure and magnetic properties of the high and low
spin states. The calculated bond length data was in line with expectations
(see Figure 2 <https://imgur.com/9hMUtYb> for the optimized unit cell
structure for high spin state and Figure 3 <https://imgur.com/feFHAYl> for
low spin state).
Then I tried to use tpssh, b3lyp and m06l functionals in QE to optimize
these spatial structures. However, for tpssh and m06l functionals, I did
not find a pseudopotential group that could make the optimization run
normally without errors (for example, the most common error is "Error in
routine cdiaghg (161): S matrix not positive definite"). On the other hand,
although the SCF converged, the b3lyp had the problem that the calculation
of "Using ACE for calculation of exact exchange" would keep looping for a
long time on a hpc cluster(see attachment 3). Therefore, I decided to try
to use CP2K to simulate the three functionals of tpssh, b3lyp and m06l.
I used Multiwfn to generate input files for high and low spin state spatial
structure optimization. The low spin state was successfully simulated using
three functionals: tpssh (expanding the cell to 2*2*2 and only counting the
Γ point, attachment 4), b3lyp (expanding the cell to 2*2*2 and only
counting the Γ point), and m06l (using the primitive cell, with the K point
of 6*6*6, attachment 5). The optimization results of the two hybrid
functionals t and b were in line with expectations (see Figures 4
<https://imgur.com/H0NeEv1> and 5 <https://imgur.com/oYAENpH>,
respectively). Although the Fe-N bond length calculated by m was in the low
spin state range, the bond lengths that should have been equal were
different (see Figure 6 <https://imgur.com/Jo2x2a9>).
In the high spin state simulation, although b3lyp (attachment 6) was able
to converge and the program successfully exited, the optimized structure
obtained was not ideal. Some of the 8 primitive cells in the supercell were
in the high spin state (Fe-N bond length was greater than 2), and some were
in the low spin state (Fe-N bond length was less than 2), and the Fe-N bond
lengths in the same primitive cell were not all equal (see Figure 7
<https://imgur.com/xm2jKsp>). When I used tpssh to optimize, the settings I
used were almost the same as those of b3lyp. However, scf did not converge
(it oscillated around 10E-5 in the output file), so I increased EPS_SCF
from 10E-6 to 10E-5 (Appendix 7) and tried the calculation again. This
time, SCF converged, but the forces in the geometry optimization (Maximum
gradient data in the output file) could not converge to the default 4.5E-4
(the closest it could get was 8E-4) after running for more than 12 hours.
After checking the pdb file of the output geometry structure change data, I
found that the overall structure only had obvious changes in the initial
optimization stage, and no longer changed in the later stage. In addition,
the later structure had similar problems as the b3lyp optimization result
(see Figure 8 <https://imgur.com/rci6EyL>). When optimizing with m06l
(input attachment 8), the SCF generally oscillates between 10-2 and 10-3
(output attachment 9). I tried some combinations of basis vectors and
pseudopotentials (https://cp2k-basis.pierrebeaujean.net/), such as the
basis vector and pseudopotentials for PBE and MGGA, but the SCF convergence
problem was not solved.
I also tried to use CP2K's PBE+D3 method (using primitive cells and 6*6*6 K
points) to optimize the high-spin state (attachment 10). After running for
more than 10 hours, the situation similar to tpssh high-spin state
simulation in which the force cannot reach the convergence limit appeared.
The output geometry structure change trajectory from pdb file is almost
stable in the later stage and the bond length and other data are consistent
with the high-spin state (see Figure 9 <https://imgur.com/n99RAWL>). In
addition, the high-spin state optimization results of PBE with 2*2*2
expanded cells as the initial guess of tpssh optimization also produced the
similar result that the force cannot reach the convergence limit in the
later stage and the optimized structure in the later stage has similar
problems as described above (see Figure 10 <https://imgur.com/Y6pIhtn>).
Then I tried to use CDFT to fix the magnetic moment of Fe, but the two
functionals pbe and tpssh (see attachment 11) I tried faced a problem that
the "Target value of constraint" and "Current value of constraint"
polarized after the program ran for a certain period of time (see
attachment 12).
Dear CP2K users, are there any problems in my various input file parameter
settings shown above? Is there any way to make the conventional DFT or CDFT
structure optimization results of tpssh, m06l or b3lyp successfully
converge to a satisfactory high spin state?
Thank you very much, your help are much appreciated.
Daniel Lee
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! total energy = -794.17980073 Ry
estimated scf accuracy < 9.0E-11 Ry
smearing contrib. (-TS) = 0.00000000 Ry
internal energy E=F+TS = -794.17980073 Ry
total magnetization = -0.00 Bohr mag/cell
absolute magnetization = 0.14 Bohr mag/cell
convergence has been achieved in 5 iterations
Using ACE for calculation of exact exchange
ACE projected onto 60 (nbndproj) and applied to 60 (nbnd) bands
total energy = -794.17980532 Ry
Harris-Foulkes estimate = -794.17980532 Ry
est. exchange err (dexx) = 0.00000458 Ry
- averaged Fock potential = 43.54602550 Ry
+ Fock energy (ACE) = -21.77302900 Ry
EXX: now go back to refine exchange calculation
total cpu time spent up to now is 595267.8 secs
per-process dynamical memory: 528.6 Mb
Self-consistent Calculation
iteration # 1 ecut= 100.00 Ry beta= 0.50
Davidson diagonalization with overlap
ethr = 1.83E-13, avg # of iterations = 9.6
total cpu time spent up to now is 595304.6 secs
total energy = -794.17980945 Ry
estimated scf accuracy < 0.00000113 Ry
total magnetization = -0.00 Bohr mag/cell
absolute magnetization = 0.14 Bohr mag/cell
iteration # 2 ecut= 100.00 Ry beta= 0.50
Davidson diagonalization with overlap
ethr = 1.13E-09, avg # of iterations = 2.0
total cpu time spent up to now is 595316.9 secs
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