[CP2K-user] [CP2K:14986] What are the default units of hartree potential and electric field in cp2k?

Fangyong Yan fyya... at gmail.com
Mon Mar 22 22:24:32 UTC 2021

```Hi, Kai,

The electric field near the point charge, which is the nuclei, can be very
large.

I think cp2k does use Hartree/Bohr, and for the large values, such as 10
Hartree/Bohr = 500 V/Angstrom, this may be due to the fact that the
eclectic field point is very close to the nuclei.

For the unit, you can ask cp2k developer to confirm, but I think it is
Hartree/Bohr, and I also think 500 V/Angstrom is correct, when it is
close to the nuclei.

Fangyong

On Mon, Mar 22, 2021 at 4:34 PM Kaixuan Chen <kaix... at gmail.com> wrote:

> Dear Fangyong,
> Thank you very much for the response. The units for the numbers of the
> cube files (both potential and electric field) is exactly what I want to
> know. They are not stated, neither in the cp2k manual nor in the cube
> files. So I try to treat the numbers in a.u. units. For example, the
> electric field cube file shows that at some positions, the number is 10
> hartree/e/bohr if the a.u. unit is the correct one. I think it is really
> huge for electric field, isn't it?
> By the way, when I mean 50000 MV/cm, I think it is equal to 50000 (10E6
> V)/(10E8 Angstrom) = 500 V/Angstrom.
> Because 1 hartree/e/bohr = 5142.20652 MV/cm, correct?
> Any suggestion on what is the default unit?
> Best,
> Kai
>
> 在2021年3月22日星期一 UTC-7 下午12:03:03<fy... at gmail.com> 写道：
>
>> Hi, Kai,
>>
>> I think you mean 5GV/cm = 500 V/Angstrom.
>>
>> I think you may need to do integration to obtain the electric field,
>> because it is a cube file, so what is the unit for the numbers
>>
>> Fangyong
>>
>> On Mon, Mar 22, 2021 at 2:25 PM Fangyong Yan <fy... at gmail.com> wrote:
>>
>>> Hi, Kai,
>>>
>>> 50000 MV/cm = 50 V / (10E8) Angstrom = 5E-7 V/Angstrom, which is a very
>>> very small electric field.
>>>
>>> Best,
>>>
>>> Fangyong
>>>
>>> On Mon, Mar 22, 2021 at 1:07 PM Kaixuan Chen <ka... at gmail.com> wrote:
>>>
>>>>
>>>> Dear all,
>>>> I have generated the cube files of hartree potential (CP2K_INPUT
>>>> <https://manual.cp2k.org/cp2k-8_1-branch/CP2K_INPUT.html> / FORCE_EVAL
>>>> <https://manual.cp2k.org/cp2k-8_1-branch/CP2K_INPUT/FORCE_EVAL.html> /
>>>> DFT
>>>> <https://manual.cp2k.org/cp2k-8_1-branch/CP2K_INPUT/FORCE_EVAL/DFT.html>
>>>> / PRINT
>>>> <https://manual.cp2k.org/cp2k-8_1-branch/CP2K_INPUT/FORCE_EVAL/DFT/PRINT.html>
>>>> / V_HARTREE_CUBE
>>>> <https://manual.cp2k.org/cp2k-8_1-branch/CP2K_INPUT/FORCE_EVAL/DFT/PRINT/V_HARTREE_CUBE.html>)
>>>> and electric field (CP2K_INPUT
>>>> <https://manual.cp2k.org/cp2k-8_1-branch/CP2K_INPUT.html> / FORCE_EVAL
>>>> <https://manual.cp2k.org/cp2k-8_1-branch/CP2K_INPUT/FORCE_EVAL.html> /
>>>> DFT
>>>> <https://manual.cp2k.org/cp2k-8_1-branch/CP2K_INPUT/FORCE_EVAL/DFT.html>
>>>> / PRINT
>>>> <https://manual.cp2k.org/cp2k-8_1-branch/CP2K_INPUT/FORCE_EVAL/DFT/PRINT.html>
>>>> / EFIELD_CUBE
>>>> <https://manual.cp2k.org/cp2k-8_1-branch/CP2K_INPUT/FORCE_EVAL/DFT/PRINT/EFIELD_CUBE.html>)
>>>> from cp2k. I don't see an explicit description on the units that are used
>>>> in these cube files. If I take the a.u. as the default unit (hartree/e for
>>>> potential, and hartree/e/bohr for electric field), the value seems pretty
>>>> large. For example, I study the single water molecule system. The largest
>>>> electric field at some density grid is 10~15 hartree/e/bohr, that is,
>>>> ~50000 MV/cm. Please correct me if I am wrong, but the value seems
>>>> unreasonable to me.
>>>> Any suggestion will be welcome, thanks in advance.
>>>> Best,
>>>> Kai
>>>>
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