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Hi Pierre,
Could you upload your input/output files for cross-checking? And and relevant fort files that contain some errors.
Cheers,
Aleks

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Either way, seems you got your geometry for further optimization
Cheers,
A

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Dear Jonas,

The basis set linear dependence issue might arise from the fact that the geometry in the scan step changes too much from the starting point and hence the interatomic distance changes a lot. Your scan step seems rather large, maybe that is the underlying issue. You can print out the geometry that will be scanned (by setting the first number as a negative values, i.e., "-1") and check that it is sensible. But perhaps I would first try with the smaller step, say 0.4 as in the first case and see if that helps.

Cheers,
Aleks

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Dear Jonas,

I took your provided data and plotted it. At first, it indeed seems as monotonically decreasing along one side of the quadratic function, but if you zoom in closely, you will notice this little "drop":

.

I suggest you do a second scanning along the same vibrational mode, but on a finer grid (e.g., step of 0.05) in the interval -1.6 / +1.6. Then take the geometry from one of the local minima (to the left and to the right of the central point, they need to be equivalent) and optimise it. The subsequent frequencies should be positive, unless there is a second negative mode or your structure is intrinsically unstable at these conditions.

Hope this helps.

Cheers,
Aleks

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Hi Chris!

You can perform a NEWK properties calculation (see page 346 of CRYSTAL User's Manual) starting from your converged wavefunction and select the printing options for eigenvalues and eigenvectors.

Hope this answers your question

Eleonora

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You can add it and sometimes it helps with the convergence but consider that the energies of the occupied orbitals are in fact shifted of the value you selected. If you want the correct value you can restart the calculation with GUESSP or plot a band structure.

Cheers,
Eleonora

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Hi masoud37!

This is because you selected LEVSHIFT in your input. Try to restart the calculation without it or plot the band structure to see the correct value of the gap.

Hope it helps,
Eleonora

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Hi,

Have you tried running a calculation where you specify the full basis set via the general route? This way one could rule out whether the internally stored basis set has some intrinsic error associated with it.

You also have DIIS turned on, which can cause issues with spin locking and cause instabilities. You can try switching it off (NODIIS) or alternatively remove spin lock, set up the spins at the beginning (ATOMSPIN) and monitor whether the DIIS is keeping the right solution.

Still might be a bug, but worth ruling out the simpler possibilities.

Hope it helps.

Cheers,
Aleks

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Dear Rams,

From your input/output files, it doesn't seem you are doing anything particularly wrong. It is more that the system is perhaps a bit more challenging. Here are a few ideas that might be of use regarding speed up and convergence:

i) You are having quite large lattice parameters (15 Angstrom in each direction). In this case having a 4x4x4 mesh of k-points is perhaps even more than needed to converge the total energy, so you can try reducing it to a 3x3x3 or 2x2x2 mesh to reduce the computational cost and get some speed up (without compromising quality). You could probably go to 1 k-point just as well, but then you might not get a correct Fermi level sampled. Which brings me to the second point...

ii) Do you expect your system to be metallic? If so, you can test a few values of the smearing parameter to see whether it makes a difference to the convergence behaviour. If you know you need to get a semiconductor, then you might want to try shifting the occupied states down in energy (keyword LEVSHIFT to prevent the system from getting stuck in a conducting state and causing the SCF to get stuck...

iii) You have the DIISALLK keyword in your input file, have you tested that as necessary for the convergence of the undoped cell? It does increase the memory/storage requirements, so could be worth trying with just the default (gamma-point) DIIS...

iv) One alternative is to turn off the DIIS convergence accelerator and revert to "classical" Fock mixing. Albeit slower in convergence than DIIS, it can stabilize the SCF procedure avoiding strong, sudden oscillation in the solution (while DIIS is turned on, the FMIXING is used only in the very first SCF step)...

v) Coming back to the charge oscillations you observed, they do indeed start appearing very quickly in your second run.
Here are the corresponding total energies from your OUTPUT_Run1.d12:

 CYC   0 ETOT(AU) -1.128999989618E+05 DETOT -1.13E+05 tst  0.00E+00 PX  1.00E+00
 CYC   1 ETOT(AU) -1.129553711002E+05 DETOT -5.54E+01 tst  0.00E+00 PX  1.00E+00
 CYC   2 ETOT(AU) -1.129699205883E+05 DETOT -1.45E+01 tst  7.60E-05 PX  9.78E-02
 CYC   3 ETOT(AU) -1.123277877060E+05 DETOT  6.42E+02 tst  4.05E+00 PX  8.33E+00
 CYC   4 ETOT(AU) -1.123934069238E+05 DETOT -6.56E+01 tst  1.68E-01 PX  6.66E+00
 CYC   5 ETOT(AU) -1.128505608381E+05 DETOT -4.57E+02 tst  2.53E-01 PX  1.17E+00
 CYC   6 ETOT(AU) -1.126570396187E+05 DETOT  1.94E+02 tst  1.41E-01 PX  1.13E+00
 CYC   7 ETOT(AU) -1.129397986733E+05 DETOT -2.83E+02 tst  1.36E-01 PX  1.16E+00
 CYC   8 ETOT(AU) -1.128184205493E+05 DETOT  1.21E+02 tst  9.81E-02 PX  6.95E-01
 CYC   9 ETOT(AU) -1.129501102455E+05 DETOT -1.32E+02 tst  9.49E-02 PX  6.74E-01
 CYC  10 ETOT(AU) -1.129223250516E+05 DETOT  2.78E+01 tst  5.80E-01 PX  6.62E-01

And then from OUTPUT_Run2.d12

 CYC   0 ETOT(AU) -1.129223250516E+05 DETOT -1.13E+05 tst  0.00E+00 PX  1.00E+00
 CYC   1 ETOT(AU) -8.145313982597E+04 DETOT  3.15E+04 tst  0.00E+00 PX  1.71E+02
 CYC   2 ETOT(AU) -1.058417907360E+05 DETOT -2.44E+04 tst  2.27E+00 PX  1.71E+02
 CYC   3 ETOT(AU) -7.201760490303E+04 DETOT  3.38E+04 tst  9.37E+00 PX  3.62E+02
 CYC   4 ETOT(AU) -3.830339502397E+04 DETOT  3.37E+04 tst  1.36E+02 PX  7.83E+02
 CYC   5 ETOT(AU) -5.612117026766E+04 DETOT -1.78E+04 tst  2.27E+01 PX  5.54E+02
 CYC   6 ETOT(AU) -1.006357459536E+05 DETOT -4.45E+04 tst  3.23E+01 PX  5.67E+02
 CYC   7 ETOT(AU) -1.131945182713E+05 DETOT -1.26E+04 tst  9.68E+00 PX  2.13E+02
 CYC   8 ETOT(AU) -1.203304661632E+05 DETOT -7.14E+03 tst  8.51E+00 PX  1.06E+02
 CYC   9 ETOT(AU) -1.148704842219E+05 DETOT  5.46E+03 tst  1.77E+01 PX  6.53E+01
 CYC  10 ETOT(AU) -1.235795679474E+05 DETOT -8.71E+03 tst  2.63E+00 PX  4.40E+01

In the first run the total energy does not oscillate, hence why the atomic charges are still somewhat as expected. In the second run, the SCF solutions starts fluctuating much more (see difference in total energies) and as a result the charges get destabilized. The SCF might not recover from that at all (even though it seems it could), so I would suggest first trying speeding up the simulation to try and get the job done in one run. Alternatively you might have to go with slower mixing and more restarts, but that is not a guarantee for a solution either. Further options include increasing the DFT grid (XXLGRID, XXXLGRID) or further increasing the last number of the integral tolerance (even though yours is pretty high already).

Hope any of this is helpful in the end!

Cheers,
Aleks

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Hi,

If I may, I'll add a few more lines on Alessandro's comment that might be of use (or not...)

Let's say you want to change the charge state of one of the Li atoms in your cell. Assuming that it is atom number XY with atomic number 3, your input might look something like this:

Title
[geometry]
END
[basis set]
...
3 3       -> Li example basis set
0 0 6 2. 1.
 700.0 0.001421
 220.0 0.003973
 70.0 0.01639
 20.0 0.089954
 5.0 0.315646
 1.5 0.494595
0 0 1 1. 1.
 0.5 1.0 
0 2 1 0. 1.
 0.6 1.0 
...
99 0
CHEMOD
1
XY             -> atom number whose charge you change for the initial guess
2.0 2.0 0.0    -> electronic charge of all shells in the basis set, here you alter the initial charge guess 
                  (note that the initial configuration is 2.0 1.0 0.0, so you will end up in the "-1" charge state)
CHARGED
END
[SCF parameters]
END

As usual, supercell size should be converged, localization of the defect confirmed, etc. Good luck with the defect formation energy corrections...one way to go is to use the multipole correction (aka Makov-Payne, see e.g., 2010 J. Phys.: Conf. Ser. 242 012004 or PRB 81, 205214 (2010))...or you can write your own piece of code to interface CRYSTAL's output to for example the scheme of Kumagai and Oba (Phys. Rev. B 89, 195205) !

Hope it helps.

Cheers,
Aleks

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