[CP2K:5389] CUTTOFF and REL_CUTTOFF for large molecular system
Tobias Kraemer
161brun... at gmail.com
Thu Jun 12 07:31:49 UTC 2014
Dear Jürg,
thank you for your detailed answer. This was very useful information,
in particular how to get an estimate of the total cutoff value,
this is very good to know. A number of things to try out now.
Cheers
Tobias
On Wednesday, June 11, 2014 1:46:55 PM UTC+1, jgh wrote:
>
> Hi
>
> some info on cutoffs:
>
> - The relative cutoff is the minimal cutoff that is used to
> integrate a Gaussian with exponent 1. This scales linearly.
> Exponent a -> a*RelCutoff.
> 40 Rydberg usually gives reasonable results.
> 60 Rydberg should be close to 'convergence'.
> 80 Rydberg should always be converged.
> !!! Remember, convergence tests always also depend on other
> factors, like the Max. Cutoff, number of grids, how subgrids are
> calculated.
>
> - Estimate of total cutoff: Max. exponent in your basis set=a
> Cutoff = 2*a*Rel_cutoff
> This is usually way too high but can be used to work your way down
> to smaller cutoffs.
>
> - For larger systems (many atoms and electrons) and dense systems,
> CPU time is not dominated by the cutoff
>
> - For some GGA functionals convergence with Cutoff can be slow.
> Dirty trick: use one of the smoothing options (XC_GRID)
> Better: use higher cutoff for XC calculation only(testing needed)
>
> - Sometimes slow convergence with cutoff points to a problem with
> the GTH pseudopotentials and GGA functionals.
> There are NLCC pseudos available that solve this issue.
> -> more testing needed
>
> regards
>
> Juerg
> --------------------------------------------------------------
> Juerg Hutter Phone : ++41 44 635 4491
> Institut für Chemie C FAX : ++41 44 635 6838
> Universität Zürich E-mail: hut... at chem.uzh.ch
> <javascript:>
> Winterthurerstrasse 190
> CH-8057 Zürich, Switzerland
> ---------------------------------------------------------------
>
> -----cp... at googlegroups.com <javascript:> wrote: -----
> To: cp... at googlegroups.com <javascript:>
> From: Tobias Kraemer <161br... at gmail.com <javascript:>>
> Sent by: cp... at googlegroups.com <javascript:>
> Date: 06/10/2014 07:06PM
> Subject: [CP2K:5389] CUTTOFF and REL_CUTTOFF for large molecular system
>
> Dear CP2K group,
>
>
> being a relatively new cp2k user, I was wondering if this group could give
> me some advice on the choice of (REL) CUTOFF values.
> The system I am considering is a somewhat extended molecular crystal
> structure, containing organometallic fragments (basically a rhodium
> phosphine complex with additional ligand plus large borate counteranions
> (BArF4-).The full system contains about 600+ atoms in the unit cell,
> basically 4 cation/anion pairs
> (asymmetric units). I think the system cannot be reduced in size, and the
> full unit cell has to be taken into account.I have attached a cif file
> which gives you
> an idea about the kind of system (not exactly the one used in the
> calculation below, but very much related)
>
> The basic idea behind determining the CUTOFF is clear to me and I have
> done the tutorial on bulk Si. I have used the same protocol for my system
> (running a series of calculations with varying CUTOFF and REL_CUTOFF
> values). In contrast to the suggested method in the tutorial, I have
> fully converged the SCF cycle) Below are the (first) results of this
> series. The energy appears to be converging towards higher CUTOFF values
> (some more calculations are currently running)
>
> (1) I wonder if choosing such a large value for the cutoff is reasonable?
> It should also increase the accuracy of the calculations, but also the
> cost.
> Also, with respect to the number of Gaussian being mapped onto the finest
> grid, what would one need to look for?
> In the tutorial the decision was based on the fact that "the distribution
> of Gaussian functions on the grids are reasonable". Could somebody
> elaborate on this
> and give me some guidance how to decide this?
> (2) How does the size of the CUTOFF value correlate with the system size,
> if there is any correlation?
> (3) Are there some rule of thumbs as how to choose the REL_CUTOFF with
> respect to the CUTOFF? For now I have tried 30, 60 and 100 Ry.
> But I may need to go to higher numbers in this particular case.
>
>
>
> # Grid cutoff vs total energy
> # Date: Tue Jun 10 17:26:55 BST 2014
> # REL_CUTOFF = 60
> # Cutoff (Ry) | Total Energy (Ha) | Charge | SCF | | NG on grid 1 | NG on
> grid 2 | NG on grid 3 | NG on grid 4
> 50.00 -4583.1402739393 -8.4046446120 200 1623260 248362
> 2112 0
> 100.00 -4477.8479306771 -0.0745436930 128 1264867 519816
> 89051 0
> 150.00 -4479.5978060995 -0.0191170935 128 1150415 472845
> 248362 2112
> 200.00 -4478.5030451759 0.0008175249 128 905641 531280
> 432781 4032
> 250.00 -4478.4529157377 -0.0000917804 128 838757 500556
> 523109 11312
> 300.00 -4478.4141842105 -0.0000534995 128 796882 467985
> 519816 89051
> 350.00 -4478.3827319182 -0.0000170792 128 748308 474790 454036
> 196600
> 400.00 -4478.3597765363 0.0000003328 128 679828 499675 489931
> 204300
> 450.00 -4478.3498795935 0.0000000149 128 621687 528728 472845
> 250474
> 500.00 -4478.3399690553 0.0000000147 128 567997 416013 600098
> 289626
> 550.00 -4478.3338555119 -0.0000000007 128 485909 446314 559882
> 381629
> 600.00 -4478.3312330111 0.0000000007 128 442629 463012 531280
> 436813
> 650.00 -4478.3291405214 0.0000000006 128 399089 473084 554024
> 447537
> 700.00 -4478.3308119206 0.0000000008 128 375655 473218 509402
> 515459
> 750.00 -4478.3298871109 0.0000000008 128 365399 473358 500556
> 534421
> 800.00 -4478.3266993684 0.0000000007 128 353459 468098 461722
> 590455
> 850.00 -4478.3266987930 0.0000000007 128 348184 458373 472494
> 594683
> 900.00 -4478.3273848891 0.0000000007 128 336984 459898 467985
> 608867
> 950.00 -4478.3277135782 0.0000000007 128 309758 476872 469877
> 617227
> 1000.00 -4478.3277705414 0.0000000008 128 291089 482269 455857
> 644519
> 1050.00 -4478.3278605666 0.0000000007 128 229036 519272 474790
> 650636
>
> Some further questions;
>
> (4) Could you recommend some literature (books) which explains the theory
> of solid state calculations, k-sampling, planewaves?
>
> (5) As a next step I would like to manipulate the structure, i.e.
> rotate/move ligands around? Is there a good visualizer that can do such
> things for periodic systems? The problem I am facing is that I would like
> to do these things simultaneously for all 4 asymmetric units.
> I think it becomes impracticable to do this for each unit separately. I
> have started using GDIS but I am a little bit uncertain about its
> abilities (great program though!!). Has anyone experience with VESTA? I am
> particularly looking for free software.
>
>
> Thank you very much for your help, this is very much appreciated. There
> are a lot of questions right a the beginning, and it is not always easy to
> find some answers.
>
> Best
>
>
> Tobias
>
>
> Dr. Tobias Kraemer
> Research Associate
> Institute of Chemical Sciences
> School of Engineering & Physical Sciences
> Heriot-Watt University
> Edinburgh EH14 4AS
> United Kingdom
>
>
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>
> [attachment "input_test.inp" removed by Jürg Hutter/at/UZH]
> [attachment "PCCPiBu_NBA.cif" removed by Jürg Hutter/at/UZH]
>
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