[CP2K-user] [CP2K:20165] Re: Hybrid functional issues

[Frederick Stein]

I am not entirely sure what exactly you do not understand. If α = -β , then 
the potential operator for HF simplifies to [α+βerf(wr)]/r = [α- α 
erf(wr)]/r = α [1-erf(wr)]/r = α erfc(wr)/r , i.e. the short-range 
operator. The shortrange operator has the advantage that it is shortranged, 
much simpler and does not need any artificial truncation whereas in the 
representation with the Coulomb and the longrange operator, you have to 
artificially truncate the Coulomb operator to obey the minimum image 
convention and ensure numerical stability (convergence issues and/or too 
large exchange energies).
xuan wang schrieb am Freitag, 3. Mai 2024 um 14:32:33 UTC+2:

> Thank you, Frederick,
> In detail, for range-separated functional, I am allowed to use 
> POTENTIAL_TYPE MIX_CL_TRUNC for wB7XD, CAM-B3LYP. The _TRUNC is truncated 
> for HF exchange, and can be truncated by CUTOFF_RADIUS from our 
> self-definition. But for HSE06, I can only use  POTENTIAL_TYPE SHORTRANGE 
> rather than type with truncated condition, because I am acquired that the 
> CUTOFF_RADIUS is defined by CP2K, not users, where this  CUTOFF_RADIUS is 
> relevant with  EPS_DEFAULT,  omega=0.11,as you said. 
>
> For range-separated functional, the coulomb operator can be seen as 1/r = 
> [1-α-βerf(wr)]/r + [α+βerf(wr)]/r. In terms of wB7XD, α = 0.222036，β = 
> 0.777964，of CAM-B3LYP, α = 0.19，β = 0.46. While in principle, HSE06 can 
> also be seen α = 0.25，β = -0.25, that we can use  POTENTIAL_TYPE 
> MIX_CL_TRUNC. But not the condition, only recommeded to use POTENTIAL_TYPE 
> SHORTRANGE. 
>
> I don't know why. I am dying for understanding why. 
>
> 在2024年5月3日星期五 UTC+8 20:13:30<Frederick Stein> 写道：
>
>> Dear Garrett,
>> If I understand your question correctly, this affects all range-separated 
>> hybrid functionals, i.e. all functionals with an explicit short/long-range 
>> Coulomb or Gaussian potential contribution. This warning is relevant if you 
>> as a user have to choose some parameters of the functional on your own. If 
>> all parameters of the functionals (CUTOFF_RADIUS, OMEGA) are pre-defined by 
>> the functional like in HSE06, you may ignore this warning. In the case of 
>> HSE06 with omega=0.11, you will probably not be able to get rid of this 
>> warning in real-case scenarios because with usual values of EPS_DEFAULT of 
>> at most 1.0E-10, this cutoff radius is at least at the order of 20 A.
>> HTH,
>> Frederick
>>
>> xuan wang schrieb am Freitag, 3. Mai 2024 um 13:50:03 UTC+2:
>>
>>> Dear all,
>>>
>>> I learned that in CP2K, the use of HSE06 for periodic calculations is 
>>> not allowed to use POTENTIAL_TYPE TRUNCATED, but POTENTIAL_TYPE SHORTANGE. 
>>> However, even SHORTANGE will also assume a cutoff_radius which is not 
>>> defined by users. 
>>>
>>> I am wondering about how many functionals behave like such HSE06? 
>>>
>>>
>>> Thank you! 
>>>
>>> Best regards,
>>> Garrett
>>>
>>

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