# [CP2K:6356] Convergence problem wrt cutoff

Matt W MattWa... at gmail.com
Wed Mar 25 15:57:31 UTC 2015

```And where do you get the potential for the Hartree integral?

On Wednesday, March 25, 2015 at 3:49:38 PM UTC, Valérie wrote:
>
> Well unless I misunderstood Quickstep is a DFT module so the coulomb term
> is just the Hartree integral
>
> On 25 March 2015 at 01:32, Matthias Krack <matth... at psi.ch <javascript:>
> > wrote:
>
>> Really, and how is the Coulomb term calculated in 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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>>>
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>
>
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