[CP2K-user] [CP2K:15690] Re: SCF convergence problem with large basis sets

[ma...@gmail.com]

Thank you Prof. Hutter. This is very helpful!

Regards,
Hongyang

在2021年7月6日星期二 UTC+10 下午6:04:35<jgh> 写道：

> Hi
>
> in GAPW calculations the electron density on the regular grids depends 
> on the soft/hard basis separation. This value will converge to some
> irregular value, but it is impossible to predict it.
> More important is the total electron density. If it is off from the
> integer number of electrons, you see errors from two sources.
> 1) the cutoff from the regular grids (as in GPW)
> 2) the atomic size approximation 
> Errors from 1) can be reduced by increasing the cutoff, errors from
> 2) are related with the rcut value of the ALL_ELECTRON file.
> "Carefully" adjusting that value can improve high precision results.
>
> regards
>
> Juerg Hutter
> --------------------------------------------------------------
> Juerg Hutter Phone : ++41 44 635 4491 <+41%2044%20635%2044%2091>
> Institut für Chemie C FAX : ++41 44 635 6838 <+41%2044%20635%2068%2038>
> Universität Zürich E-mail: h... at chem.uzh.ch
> Winterthurerstrasse 190
> CH-8057 Zürich, Switzerland
> ---------------------------------------------------------------
>
> -----c... at googlegroups.com wrote: -----
> To: "cp2k" <c... at googlegroups.com>
> From: "ma... at gmail.com" 
> Sent by: c... at googlegroups.com
> Date: 07/06/2021 01:56AM
> Subject: [CP2K:15690] Re: SCF convergence problem with large basis sets
>
> Hi Nick,
>
> Just curious about your third suggestion (the CUTOFF issue). 
> When I use ALL_ELECTRON basis sets, I found increasing CUTOFF does not 
> change the second value of "Electronic density on regular grids" at all, 
> although the SCF converged energy is decreasing. I tried DZVP all electron 
> basis set for Si. But even using a CUTOFF as high as 1000 Ry, the second 
> value of "Electronic density on regular grids" is still 13.5173370396 
> <(517)%20337-0396> same as CUTOFF of 50 Ry. I'm wondering do I need to 
> worry about this when I use ALL_ELECTRON basis sets?
>
> Regards,
> Hongyang
>
> 在2021年7月6日星期二 UTC+10 上午8:49:27<n... at berkeley.edu> 写道：
>
> Tom,
>
> (1) When you say that you had no issues with DZVP -> TZVP -> TZV2P basis 
> sets, were you using the MOLOPT basis sets? The MOLOPT basis sets were 
> optimized using the overlap matrix condition number as a constraint in 
> order to make them more numerically stable. This is why they are the basis 
> set type of choice for condensed phases. If you *were* using MOLOPT, then 
> once you move to the QZVP basis sets, for which there are no molopt basis 
> sets, then that is why it become harder to converge. If you *were not* 
> using the MOLOPT basis sets I would encourage you to stick with them. 
> Generally, condensed matter systems have converged properties around TZVP 
> quality in my opinion, and DZVP is still pretty good. If you need true 
> chemical accuracy, then you're going to need to move beyond DFT anyway.
>
> (2) There is a general issue of using larger basis sets, which is the 
> nature of the Gaussian type orbitals. GTOs are not an orthonormal basis, 
> unfortunately, so the larger your basis set, the greater the risk of 
> introducing linear dependencies that make converge very difficult. Another 
> reason to limit the size to only as large as you need for your application. 
> Beyond linear dependencies, the conditioner number itself also increases 
> with increasing basis set size.
>
> (3) Your CUTOFF in your multi-grid is not converged. I noticed this 
> because after your SCF loops you have the line "Electronic density on 
> regular grids. -605.9997903253 0.0002096747" -- the second number in this 
> column should be <1e-8 preferably. The cutoff is the most common cause for 
> this, and your cutoff of 350 is not sufficient. To determine the cutoff, 
> take the largest exponent in your basis set and multiply it by the relative 
> cutoff. Your CUTOFF value should be at least this large, otherwise your 
> multigrid will not be able to accommodate the hardest exponents. Oxygen has 
> an exponent of ~12 at the QZV3P level of theory, so your CUTOFF should be 
> around 480 if you are using the default REL_CUTOFF of 40. The exponents 
> change with your basis set, so this could be part of the issue you were 
> facing when you got to the larger ones.
>
> Try fixing your CUTOFF value and see if it helps, but also consider using 
> smaller basis sets, maybe of the MOLOPT type, which are generally 
> sufficiently accurate for most DFT calculations. 
>
>
> -Nick
> On Monday, July 5, 2021 at 5:02:47 AM UTC-7 tom... at ugent.be wrote:
> Sorry forgot the attachments.
>
> On Monday, July 5, 2021 at 1:44:50 PM UTC+2 Tom Braeckevelt wrote:
> Dear CP2K users/developers,
>
> I was performing some benchmarks related to the basis set size (with 
> simply PBE-D3). In particular, I was checking the energy difference between 
> benzene adsorbed in the H-SSZ-13 zeolite and its protonated counterpart. 
> While I can see a steady improvement going from DZVP -> TZVP -> TZV2P 
> (without any issue in the calculation) I encountered large problems in the 
> SCF convergence when using even larger basis sets, like the QZV2(or 3)P and 
> the augmented basis sets. At this point, I was only able to converge a 
> couple calculations with the QZV3P using the CG optimizer (normally I use 
> the DIIS) and the FULL_KINETIC preconditioner (I normally use the 
> FULL_SINGLE_INVERSE), which according to the manual should be more robust. 
> I also tried the diagonalization method instead of the OT one but also in 
> that case the scf was not converging.
> The problem is that even with the two converged calculations the energy 
> difference between the two species I'm studying results to be ~3000kJ/mol 
> vs the expected ~100kJ/mol, thus it looks like the two scf have converged 
> to different minima.
>
> Does anybody know how to robustly converge the scf with large basis sets? 
> In attachment the input and output of the supposedly converged calculations.
>
> Thank you in advance,
> Tom
>
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