Re: External pseudopotentials and large structures ( No.1 ) 
 Date: 2017/04/20 17:02
 Name: T. Ozaki
 Hi,
I checked your PAO (nb.pao) and VPS(nb.vps), found that nb.pao looks okay. However, it turns out that the local potential is extremely deep at the origin. I think that the large variation of the potential in the vicinity of the origin is enough to cause the numerical problem. The local potential is used to construct the neutral atom potential, which leads to a quite deep neutral atom potential at the origin. Since you employ the projector expansion method with "scf.BufferL.VNA 6" "scf.RadialF.VNA 11", I wonder that the large variation cannot be well reproduced by such a parameter set. Also please note that the projector expansion is NOT applied to a dimer case as discussed in our paper: http://www.openmxsquare.org/tech_notes/tech15.pdf The fact might be related to the fact that your calculation for the dimer looks okay.
To check this, you may perform the calculations with the NONprojector expansion method with very high cutoff energy of several thousands Ryd. By comparing results with/without the projector expansion method, you may be able to narrow down possible sources of the problem.
Also, I noticed that your projet.energie seems to be quite large in some channel. I guess that this might be related to the large rounding off error, resulting in ghost states.
If you would like to use your PAO and VPS, you need to identify very carefully places in the code where numerical instabilities take place, while this will require considerable efforts.
Best regards,
TO

Re: External pseudopotentials and large structures ( No.2 ) 
 Date: 2017/04/20 23:05
 Name: Daniil
 Thanks.
Theoretically, I can increase the minimum R value of vps grid, in order to 'hide' singularity. This will lead to a loss of precision, but that's better than a completely wrong result. Probably, I'll try to estimate this effect.
Do you mean Nb2Cl10 by 'dimer'? If so, could you please clarify, why the projector expansion is not applied there? I briefly read the paper, but didn't found the particular statement about it.
As for cutoff, do you mean scf.energycutoff, or 1DFFT.EnergyCutoff?
Also, as I understand from Blochl projector form, it is possible to decrease project energies and vectors in a same way as it is done for MBK scheme in ADPACK, where energies are normalized to 1. What limits for energies are recommended?
Best regards, Daniil

