[CP2K-user] [CP2K:19498] Switching from GPW to GAPW

[Léon Luntadila Lufungula]

Dear Prof. Hutter,

Thanks for pointing me into the right direction!

Unfortunately, the defaults are not sufficient for my system as I am 
getting rather large values for the lines you suggested to check:

(Inner SCF loop 1)
  Total charge density (r-space):                      0.0000427891
  Total Rho_soft + Rho0_soft (g-space):         0.0001310539
(Inner SCF loop 2)
  Total charge density (r-space):                      0.0000494000
  Total Rho_soft + Rho0_soft (g-space):         0.0001376711

I have attached my input file and the short part that was written to the 
output if you would like to see it in more detail. My system consists of a 
TiO2 [anatase (101)] slab with organic molecules adsorbed onto the surface, 
so I suspect that it might be the Ti atoms for which the defaults are 
insufficient.

I have been looking into GAPW in the regtests, documentation and forum over 
the last couple of days and from what I understand, the most important 
parameters to change should be the following:
(FORCE_EVAL / SUBSYS / KIND)

   - *LEBEDEV_GRID*: I'm a bit unsure how to get a correct value for this 
   parameter for each atom kind. Does this involve a convergence test for each 
   atom type individually or is there some rule of thumb?
   - *RADIAL_GRID*: same as for LEBEDEV_GRID.

(FORCE_EVAL /DFT / QS)

   - *EPS_DEFAULT*: This one is already at 1.0E-12, should I reduce it 
   further?
   - *EPS_FIT*: The default is 1.0E-4, but I've read in another post in a reply 
   from M. Krack 
   <https://groups.google.com/g/cp2k/c/FUvjXq9RvWY/m/8VwHvHGUAgAJ> that it 
   is too large for most systems and should be reduced to 1.0E-6. Should I 
   reduce it in my case?
   - *EPS_ISO*: I've seen it mentioned a couple of times, but never if the 
   value should be reduced or what to do with it exactly.
   - *EPS_RHO0*: According to the reply of M. Krack 
   <https://groups.google.com/g/cp2k/c/FUvjXq9RvWY/m/8VwHvHGUAgAJ> smaller 
   values than the default give better accuracy.

(FORCE_EVAL / DFT / MGRID)

   - *CUTOFF*: This is generally lower than for a GPW calculation as I 
   understand it but I guess I should perform a convergence test to choose an 
   appropriate value. Alternatively, I could also multiply the relative cutoff 
   by the maximum exponent in the soft basis set (PRINT_LEVEL MEDIUM to get 
   the values right?) as you and Marcella suggested in another post 
   <https://groups.google.com/g/cp2k/c/JX8bDi_w478/m/okVfMy6EAQAJ>.
   - *REL_CUTOFF*: I'm a bit unsure about how to choose this as all the 
   convergence schemes I've read about first converge the CUTOFF with a large 
   REL_CUTOFF and then reduce the value of REL_CUTOFF to get the best balance 
   between accuracy and efficiency, but as explained above, the rule of thumb 
   for the cutoff uses the value of REL_CUTOFF to determine the CUTOFF...

Any suggestions on how to optimize these parameters would be greatly 
appreciated!

I also have two other quick questions about your reply:

   1. I thought that GPW was used for pseudopotential calculations and GAPW 
   was used for all electron calculations, but now you say that you can also 
   do pseudopotential calculations with GAPW. Is there an advantage to using 
   GAPW over GPW? I know that the disadvantage is that some features are not 
   present for GAPW calculations, but is there a reason to use GPW if all your 
   intended features are implemented for GAPW?
   2. The BASIS_MOLOPT_UZH file contains SVP,- TZVPP- and 
   QZVPP-MOLOPT-GGA-ae basis sets. Is there also a double zeta all electron 
   (MOLOPT) basis set somewhere I can use? I have always been told that single 
   zetas are not intended for production runs, but I suspect that TZVPP is 
   already quite computationally expensive for a pre-optimization.

My apologies for the barrage of questions, but I don't have anyone in my 
group with experience in CP2K so it's hard sometimes to figure these things 
out on my own...

Thanks in advance and for your previous reply!

Kind regards,
Léon
On Tuesday, 14 November 2023 at 10:51:05 UTC+1 Jürg Hutter wrote:

> Hi
>
> For a pseudopotential calculation you can just change "METHOD GPW" to
> "METHOD GAPW".
> If you want to do all electron calculations, you also need to use 
> corresponding
> basis sets and potentials, e.g.
> BASIS_SET SVP-MOLOPT-GGA-ae
> POTENTIAL ALL
> Use the default settings first, check the lines
> Total charge density (r-space): -0.0000000683
> Total Rho_soft + Rho0_soft (g-space): -0.0000000043
> in the output. If those values are larger than 0.00001 you need probably to
> change defaults.
> See the regtests and manual for more information.
> Come back here for if this basic setup fails.
>
> regards
> JH
>
> ________________________________________
> From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of Léon 
> Luntadila Lufungula <Leon.luntad... at uantwerpen.be>
> Sent: Wednesday, November 8, 2023 5:21 PM
> To: cp2k
> Subject: [CP2K:19481] Switching from GPW to GAPW
>
> Dear all,
>
> I want to perform an AIM analysis with Critic2 which (for as far as I 
> know) requires an all-electron density (i.e. not the density obtained from 
> a GPW calculation) and also plan to calculate NMR chemical shifts in the 
> future which will also require the all-electron GAPW method. Currently, I 
> have figured out how to do calculations with the GPW method but I'm still a 
> bit unsure about how to go from a GPW to a GAPW calculation. Is there 
> someone who could elaborate on what to look at when modifying my input 
> file? I've looked into it a couple of times, but it's a lot of different 
> parameters and I can't seem to figure out how it works...
>
> All the best,
> Léon
>
>
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