[CP2K-user] [CP2K:22098] Re: Confusion about the D4 parameters

[Johann Pototschnig]

1+2)
The  Coordination number function type (cnfun) determines which definition 
for the coordination number calculation is used:
  1 - D3
  2 - new D3
  3 - D4
which updates the Cutoff radius coordination number. 
Therefore, the value from the input is not used. This probably should be 
fixed, I will open an issue. 

3) Yes, the values from the dftd4 github are used. 
     As far as I can see, at the github the same set of parameters is used.
https://github.com/dftd4/dftd4/blob/dd4884f0a7abde2bdbed61e035a25e805a3c84ad/src/dftd4/param.f90#L292

If you want to use parameters defined somewhere else it might be necessary 
to extend the input. 

best,
Johann Pototschnig




On Monday, February 9, 2026 at 2:47:14 PM UTC+1 Torstein Fjermestad wrote:

> CP2K version 2025.2
>
>  Dear all, 
>
>  I am running some test calculations using the D4 dispersion together with 
> the m06 functional. 
>
> I am confused about some of the parameters in the input and how these 
> correspond to information in the output. 
>
> My VDW_POTENTIAL section looks like the following:
>
>  
>
>       &VDW_POTENTIAL
>        POTENTIAL_TYPE PAIR_POTENTIAL
>        &PAIR_POTENTIAL
>         TYPE DFTD4
>         D4_CN_CUTOFF 5.29177209
>         D4_CUTOFF 1.05835442E+001
>         D4_DEBUG T
>         D4_REFERENCE_CODE F
>         FACTOR_S9_TERM 1.00000000E+000
>         REFERENCE_FUNCTIONAL m06
>         R_CUTOFF 1.05835442E+001
>         VERBOSE_OUTPUT T
>         &PRINT_DFTD DEBUG
>         &END PRINT_DFTD
>        &END PAIR_POTENTIAL
>       &END VDW_POTENTIAL
>
>  
>
> The value of D4_CN_CUTOFF is the suggested value in the manual. 
>
>  
>
> In the output, the following information is printed:
>
>  
>
>
>  !-----------------------------------------------------------------------------!
>                                DEBUG D4 DISPERSION
>
>  !-----------------------------------------------------------------------------!
>  DEBUG D4| Reference functional                                           
>    m06
>  DEBUG D4| Scaling parameter (s6)                                         
> 1.0000
>  DEBUG D4| Scaling parameter (s8)                                         
> 0.1637
>  DEBUG D4| BJ Damping parameter (a1)                                     
>  0.5346
>  DEBUG D4| BJ Damping parameter (a2)                                     
>  6.0619
>  DEBUG D4| Cutoff value coordination numbers                         
>  0.1000E-05
>  DEBUG D4| Cutoff radius coordination numbers                           
>  11.1000
>  DEBUG D4| Coordination number function type                               
>     3
>  DEBUG D4| Cutoff radius 2-body terms [bohr]                             
> 40.0000
>  DEBUG D4| Cutoff radius 3-body terms [bohr]                             
> 40.0000
>  DEBUG D4| CN differences (max)                                         
> 0.000001
>  DEBUG D4| CN differences (ave)                                         
> 0.000000
>
>  
>
> I have the following questions regarding this output section:
>
>
>    1. I don't understand what "Cutoff radius coordination numbers" means. 
>    I could guess that it is the value of the input parameter D4_CN_CUTOFF, but 
>    the value does not match. If D4_CN_CUTOFF is converted from Ångstrøm to 
>    Bohr in the output, the value should be 10 and not 11.1. Is the value of 
>    D4_CN_CUTOFF in the input ignored?
>    2. What does “Coordination number function type” refer to?
>    3. By comparing the values of the scaling and BJ damping parameters to 
>    the values of the dftd4 Github web page, I see that the ATM values are 
>    used. Is there an input option for choosing the many-body dispersion 
>    parameters instead?
>
>
> Thanks in advance for your help. 
>
> Best regards,
>
> Torstein
>
>  
>

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