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

Kaixuan Chen kaix... at gmail.com
Tue Mar 23 21:02:11 UTC 2021

```Hi Fangyong,
Kai

> 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 <ka... 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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