# [CP2K:6354] Convergence problem wrt cutoff

Matthias Krack matthia... at psi.ch
Wed Mar 25 05:32:38 UTC 2015

```Really, and how is the Coulomb term calculated in a Quickstep run?

Matthias

On Wednesday, 25 March 2015 01:06:29 UTC+1, Valérie wrote:
>
> Thanks Matthias for looking at it again. I don't think I need a Poisson
> section for a Quickstep calculation tho, I would only solve Poisson
> equation if I were to compute a classical potential energy
>
> Valerie
>
> On 24 March 2015 at 17:58, Matthias Krack <matth... at psi.ch> wrote:
>
>> A further observation: you specify PERIODIC NONE in the &CELL section,
>> but there seems to be no &POISSON section with the same setting.
>>
>> Matthias
>>
>>
>> On Tuesday, 24 March 2015 19:03:45 UTC+1, Valérie wrote:
>>>
>>> Dear Matthias,
>>>
>>> Thanks for the advice, I tried EPS_DEFAULT 1.0E-14 and turn off the
>>> smearing but it didn't help:
>>>
>>> # Grid cutoff vs total energy
>>> # REL_CUTOFF = 100
>>> # Cutoff (Ry) | Total Energy (Ha) | NG on grid 1 | NG on grid 2 | NG on
>>> grid 3 | NG on grid 4
>>>      50.00   -68.6591151507   51528     490       0       0
>>>     100.00   -71.4960225951   49423    2499      96       0
>>>     150.00   -71.3943595587   46649    4879     490       0
>>>     200.00   -71.4042101807   45019    6209     790       0
>>>     250.00   -71.4043240457   42959    7117    1846      96
>>>     300.00   -71.4043467391   41354    8069    2499      96
>>>     350.00   -71.4042672401   38632   10347    2847     192
>>>     400.00   -71.4043262818   37146   10913    3671     288
>>>     450.00   -71.4043453432   35187   11462    4879     490
>>>     500.00   -71.4043447554   34568   11773    5187     490
>>>     550.00   -71.4043353326   33159   11988    6081     790
>>>     600.00   -71.4043429773   32597   12422    6209     790
>>>
>>>
>>>
>>> On Tuesday, March 24, 2015 at 12:51:04 PM UTC-4, Matthias Krack wrote:
>>>>
>>>>  Dear Valerie,
>>>>
>>>> you may try a smaller EPS_DEFAULT value like 1.0E-12 or even 1.0E-14.
>>>> You may also switch off the smearing, if your systems shows a decent band
>>>> gap. I would guess a cutoff of about 400 Ry should be sufficiently accurate.
>>>>
>>>> Matthias
>>>>
>>>> On 24/03/15 17:40, Valérie wrote:
>>>>
>>>> Hi all,
>>>>
>>>> I would like to run a geometry optimization of a single molecule with
>>>> Quickstep but got stuck at the first step; i.e. get meaningful values of
>>>> cutoff and relative cutoffs.
>>>> I followed this tutorial: http://www.cp2k.org/howto:converging_cutoff
>>>> but the total energy does not converge to great accuracy with my system:
>>>>
>>>> # Grid cutoff vs total energy
>>>> # REL_CUTOFF = 100
>>>> # Cutoff (Ry) | Total Energy (Ha) | NG on grid 1 | NG on grid 2 | NG on
>>>> grid 3 | NG on grid 4
>>>>      50.00   -68.6591152269   51340     490       0       0
>>>>     100.00   -71.4960226714   49235    2499      96       0
>>>>     150.00   -71.3943596348   46461    4879     490       0
>>>>     200.00   -71.4042102566   44831    6209     790       0
>>>>     250.00   -71.4043241216   42771    7117    1846      96
>>>>     300.00   -71.4043468150   41166    8069    2499      96
>>>>     350.00   -71.4042673160   38450   10341    2847     192
>>>>     400.00   -71.4043263577   36970   10901    3671     288
>>>>     450.00   -71.4043454189   35016   11445    4879     490
>>>>     500.00   -71.4043448309   34404   11749    5187     490
>>>>     550.00   -71.4043354081   33007   11952    6081     790
>>>>     600.00   -71.4043430530   32450   12381    6209     790
>>>>
>>>> I was wondering if there was something I could try to fix this or
>>>> should I carry on with Cutoff = 400?
>>>>
>>>> Many thanks
>>>> Valerie
>>>>
>>>>
>>>>   --
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