# [CP2K-user] [CP2K:16699] Re: Point charges to simulate an electric field?

Matt Watkins mattwatkinsuk at gmail.com
Fri Mar 11 12:13:43 UTC 2022

```Hi,
those you list are Hirshfeld charges that are defined geometrically without
reference to a basis set (intergrated density in some radius or similar).
If you look at Mulliken charges those should be as you expect.
At a glance the setup looks right to me.
Matt

On Sunday, 6 March 2022 at 00:28:30 UTC dr.bra... at gmail.com wrote:

> Thanks.
> OK, I think I get it now.
> So I have set CHARGE keyword to 25, since I want to have 25 fake H atoms
> and each to represent smeared charge of +0.28e, and the rest of my system
> in neutral.
> My KIND section now:
>
>
>
>
>
>
> *    &KIND X      ELEMENT H      BASIS_SET NONE      POTENTIAL GTH-PBE-q1
>     CORE_CORRECTION -0.88    &END KIND*
>
> However, when I perform population analysis I find finite population on
> these fake atoms:
>
>
>
>
>
>
>
>
>
>
>
> *Hirshfeld Charges  #Atom  Element  Kind  Ref Charge     Population
>              Net charge      1       H      1       0.280          0.046
>                       0.234      2       H      1       0.280
>  0.047                         0.233      3       H      1       0.280
>      0.052                         0.228      4       H      1       0.280
>          0.055                         0.225      5       H      1
> 0.280          0.046                         0.234      6       H      1
>     0.280          0.051                         0.229.*
> *.*
> *.*
>
> How is this possible when they are described with no basis at all?
>
> Best,
> BM
>
> On Wednesday, March 2, 2022 at 5:04:08 PM UTC+1 mattwa... at gmail.com wrote:
>
>> There will be the core charge of the original atom as well - so you need
>> Yes - the charge keyword will alter the number of electrons in the system
>> so if you want these to be virtual protons not hydrogen atoms then you do
>> need to remove the electron as well with the charge keyword.
>> If your overall system is charged then normal issues of charged periodic
>> systems apply..
>> Matt
>>
>> On Monday, 28 February 2022 at 12:37:58 UTC dr.bra... at gmail.com wrote:
>>
>>> Additionally, should I in such cases change total charge od the system?
>>>
>>> On Wednesday, February 23, 2022 at 2:09:59 PM UTC+1 Бранислав
>>> Миловановић wrote:
>>>
>>>> Thanks, just want to check if this is right way to do this:
>>>> I defined atoms labeled *X* in the coord file and then I added this
>>>> section into the SUBSYS:
>>>>
>>>>     &KIND X
>>>>       ELEMENT H
>>>>       GHOST .TRUE.
>>>>       BASIS_SET NONE
>>>>       POTENTIAL GTH-PBE-q1
>>>>       CORE_CORRECTION 0.12   # 3/25
>>>>     &END KIND
>>>>
>>>> Is this the right way to divide for example 3*e* charge over 25 fake
>>>> hydrogen atoms?
>>>>
>>>> Branislav
>>>>
>>>> On Monday, February 21, 2022 at 4:31:49 PM UTC+1 mattwa... at gmail.com
>>>> wrote:
>>>>
>>>>> Multiple options - most directly:
>>>>>
>>>>> https://manual.cp2k.org/cp2k-9_1-branch/CP2K_INPUT/FORCE_EVAL/SUBSYS/KIND.html#list_CORE_CORRECTION
>>>>> lets you change the core charge on a pseudopotential. If you make a
>>>>> fake hydrogen and adjust charge appropriately you'd get close to what you
>>>>> were after (won't be a point charge but gaussian smeared charge).
>>>>>
>>>>> There are other routines that could load an external potential on a
>>>>> grid or make use of the QM/MM code in some form.
>>>>> Matt
>>>>>
>>>>>
>>>>> On Monday, 21 February 2022 at 15:24:34 UTC dr.bra... at gmail.com wrote:
>>>>>
>>>>>> Dear cp2k users,
>>>>>>
>>>>>> Is it possible to introduce ghost atoms with no basis set and with
>>>>>> finite non-integer point charge in AIMD calculations? Something like MM
>>>>>> point charges.
>>>>>>
>>>>>> I want to try to simulate behaviour of some small molecules in the
>>>>>> electric field which originates from a particular sequence of the point
>>>>>> charges.
>>>>>>
>>>>>> Thanks
>>>>>> Branislav
>>>>>>
>>>>>

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