[CP2K-user] [CP2K:22094] Confusion about the D4 parameters

[Torstein Fjermestad]

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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