[CP2K-user] [CP2K:18893] Re: Problems with converging PW cutoff

[Lobna Saeed]

I didnt identify anything wrong with cp2k pseudopotentials or basis sets.
But we also all know that with some elements we need to do optimization for
basis sets, at least !

On Mon, Jun 5, 2023 at 11:50 AM Jürg Hutter <hutter at chem.uzh.ch> wrote:

> Hi
> please only compare codes for quantities that can be transferred. For
> example, it is almost
> impossible to compare total energies. Relative energies or other
> properties can be
> compared for equivalent settings.
> If you have identified a pseudopotential/basis set problem for CP2K,
> please provide us with the
> necessary information and we will investigate.
> Thank you
> JH
>
> ________________________________________
> From: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of Lobna
> Saeed <lobna.saeed at gmail.com>
> Sent: Monday, June 5, 2023 9:18 AM
> To: cp2k at googlegroups.com
> Subject: Re: [CP2K:18885] Re: Problems with converging PW cutoff
>
> I had the same exact issues with the convergence !! exactly the same. I
> was also confused about the largest exponent as well. When I used this
> https://www.cp2k.org/faq:cutoff, I got a very high cutoff value which
> when I employed deviated very much from the experimental values. So may be
> you need to look at other values, other than the total energies. The total
> energies we get here are not by any mean realistic. When I compared the
> total energy values I got from VASP with the values we get from CP2K (for
> single elements), I got completely different results. So when I increased
> the basis sets I was able to get the same values for Al and Nb, other
> elements like Ti REALLY need optimization of the basis sets and
> pseudopotentials. Therefore you should try to look at other values other
> than the total energies (like the lattice parameters for example) to be
> able to deduce a final conclusion about the cutoff value.
>
> On Mon, Jun 5, 2023 at 6:59 AM Léon Luntadila Lufungula <
> Leon.luntadilalufungula at uantwerpen.be<mailto:
> Leon.luntadilalufungula at uantwerpen.be>> wrote:
> Dear all,
>
> Apparently I forgot to add my input file in my previous message, so I have
> included it as an attachment in this reply. I'm eagerly looking forward to
> your replies and thank you in advance.
>
> Kind regards,
> Léon
>
> On Friday, 2 June 2023 at 15:44:38 UTC+2 Léon Luntadila Lufungula wrote:
>
> Dear all,
>
>
>
> I am currently switching from Quantum ESPRESSO (QE) to CP2K as my main
> computational software package (currently using version 8.2) and I am
> struggling a bit with the convergence tests for the PW cutoffs (REL_CUTOFF
> and CUTOFF). My intended structures to investigate are moderate-sized
> organic molecules adsorbed onto a (101) surface of anatase (TiO2) and as
> such I am using an optimized structure from my QE calculations as a
> representative system to do my convergence tests on (see attached file
> 3mppa-md1.inp). I based my method on the method proposed by Prof. Hütter in
> a previous post<https://groups.google.com/g/cp2k/c/ySUAYEgwmhc>, whereby
> I first set REL_CUTOFF=CUTOFF and increase the value until I reach
> convergence. The results I got are the following:
>
>
>
> # Grid cutoff vs total energy
>
> # Date: Fri Jun  2 14:09:32 CEST 2023
>
> # PWD: /home/lluntadilal/cp2k/scf/dft/test/final/convergence/cutoff
>
> # Cutoff (Ry) | Relative cutoff (Ry) | Total energy (a.u.) | Total charge
> (a.u.)
>
>           300                    300
> -3303.4693919783<tel:(469)%20391-9783>          0.0000049144
>
>           400                    400      -3303.4678396250
>  -0.0000000118
>
>           500                    500      -3303.4658109937
>  -0.0000000003
>
>           600                    600      -3303.4675587607
>  -0.0000000003
>
>           700                    700      -3303.4671967038
>  -0.0000000003
>
>           800                    800      -3303.4663947747
>  -0.0000000003
>
>           900                    900      -3303.4659684557
>  -0.0000000003
>
>          1000                   1000      -3303.4657584430
>  -0.0000000002
>
>          1100                   1100      -3303.4651289391
>  -0.0000000002
>
>          1200                   1200      -3303.4650897922
>  -0.0000000003
>
>          1300                   1300      -3303.4651986119
>  -0.0000000002
>
>          1400                   1400      -3303.4651800964
>  -0.0000000002
>
>          1500                   1500      -3303.4650037920
>  -0.0000000002
>
>          1600                   1600      -3303.4650956961
>  -0.0000000002
>
>          1700                   1700      -3303.4651701336
>  -0.0000000002
>
>          1800                   1800      -3303.4651578599
>  -0.0000000002
>
>          1900                   1900      -3303.4651999129
>  -0.0000000002
>
>          2000                   2000      -3303.4651936486
>  -0.0000000002
>
>
>
> I have several questions about this:
>
>   1.  I would like to be able to give the energies of my structures
> accurate up to 0.01 kJ/mol which is about 1.10^-6 a.u. Unfortunately, I
> only reach this level of accuracy at a cutoff of 2000 Ry… This seems quite
> a large cutoff as I see similar calculations with cutoffs between 400-1200
> Ry and also because the charge is already converged at 500 Ry. Am I doing
> something wrong or is my criteria just too strict? Does this perhaps have
> anything to do with the fact that the relative position of the atoms to the
> grid points changes with the cutoff as mentioned by Prof. Hütter in his
> post?
>   2.  The faq<https://www.cp2k.org/faq:cutoff> and converging cutoff
> exercise<https://www.cp2k.org/events:2018_summer_school:converging_cutoff>
> state that the PW cutoff should be large enough to properly represent the
> Gaussian with the largest exponent, which in my system seems to be oxygen
> with an exponent around 10.4 for the DZVP-MOLOPT-SR-GTH basis set. So is it
> then correct to use such a complex structure (3-layer slab with adsorbate
> and 30Å vacuum width) with "complex" options (dipole and dispersion
> corrections) as input for my convergence tests or could I use a simpler
> structure (e.g. an oxygen molecule in a box) with more basic settings (no
> corrections) or would this be insufficient?
>   3.  I may be planning to use larger basis sets ("regular" DZVP, TZVP or
> TZV2P) of the MOLOPT family in the future and I have seen that the largest
> exponents for these sets is the same as that for the smaller DZVP-SR basis
> set (10.4 for oxygen). Is it correct then to assume that once I obtain
> optimized cutoffs for DZVP-SR, these can be kept when switching to any of
> the larger basis sets?
>   4.  Lastly, I would like to ask for some general feedback on the input
> for my slab calculation as this is my first calculation on CP2K and I'm
> still getting used to all the settings. Is it okay to use 3D periodicity
> with a large vacuum space and a dipole correction or is it better to use 2D
> periodicity with a corresponding Poisson solver (e.g. MT, analytic or
> wavelet)? Is it okay to use the WC functional with basis sets,
> pseudopotentials and D3 settings optimized for PBE?
>
>
>
> Any help would be greatly appreciated!
>
>
>
> Kind regards,
>
> Léon
>
>
>
> P.S. For those looking at my structure in a graphical environment and
> noticing that some atoms are outside the unit cell. This is due to the fact
> that my cell was monoclinic and I made the unit cell orthorhombic to save
> computational time and trouble (some codes have trouble dealing with cells
> that are not orthorhombic), but I did not yet wrap all my atoms into the
> unit cell. However, I don't think this should be a problem under PBC.
>
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