[CP2K-user] [CP2K:21009] Re: CAM_B3LYP usage

[Beliz Gökmen]

Hi Miguel,

Your setup of the XC_FUNCTIONAL is correct, you are only missing this 
section inside HF:
         &INTERACTION_POTENTIAL
            POTENTIAL_TYPE MIX_CL_TRUNC
            CUTOFF_RADIUS ${cutoff}
            OMEGA 0.33
            SCALE_COULOMB 0.19
            SCALE_LONGRANGE 0.46
            T_C_G_DATA t_c_g.dat
         &END
This is needed for the mixed short-range long-range part of the functional. 
Furthermore, the HF fraction should be set to 1.0, otherwise all these 
values in the interaction potential will be multiplied by the number you 
specify. The cutoff value should be around half the cell length.

It is not straightforward to compare the cp2k values to gaussian, as 
gaussian uses VWN3 local correlation functional whereas cp2k uses VWN5 for 
B3LYP. 

Another comment is that your cutoff value for the vdw pair potential is 
larger than your cell size, you might want to check this. Also, since you 
have a runtype geo_opt, I assume you are interested in optimising the 
geometry of the first excited state. Then you should include
  &EXCITED_STATES
    STATE 1
  &END EXCITED_STATES
in DFT, where the state should be the state of interest.

Best,
Beliz

On Sunday, 5 January 2025 at 03:52:15 UTC-6 Miguel RP wrote:

> Hi All,
>
> I am attempting to perform a TD-DFT calculation using the CAM-B3LYP 
> functional on a simple 3-atom titania system. However, the energies I am 
> obtaining differ significantly from those produced by a different code 
> (Gaussian), even if I use the same functional and all-electron basis-set. 
> Interestingly, when using the B3LYP functional, the results align well with 
> Gaussian outputs. This suggests that the discrepancy is likely due to 
> incorrect usage or configuration of the CAM-B3LYP functional with this 
> titania system (in the past I got reasonable values with same functional 
> applied to a formaldehyde molecule)
>
> Below is the relevant section of my input file, specifically the XC 
> definition:
>
>   &XC
>       &XC_FUNCTIONAL
>         &HYB_GGA_XC_CAM_B3LYP
>           _AC 0.81
>           _ALPHA 0.65
>           _BETA -0.46
>           _OMEGA 0.33
>         &END HYB_GGA_XC_CAM_B3LYP
>       &END XC_FUNCTIONAL
>       &HF
>         &SCREENING
>           EPS_SCHWARZ 1.0E-12
>         &END
>         &MEMORY
>           MAX_MEMORY  10000
>           EPS_STORAGE_SCALING 0.1
>         &END MEMORY
>         FRACTION 0.19
>       &END
>       &VDW_POTENTIAL
>          POTENTIAL_TYPE PAIR_POTENTIAL
>          &PAIR_POTENTIAL
>             PARAMETER_FILE_NAME dftd3.dat
>             TYPE DFTD3
>             REFERENCE_FUNCTIONAL B3LYP
>             R_CUTOFF [angstrom] 16
>          &END
>       &END VDW_POTENTIAL
>     &END XC
>
> I am uncertain about the correct value for the "FRACTION" parameter in the 
> HF section. Should this parameter align somehow with the _ALPHA, _BETA, and 
> _OMEGA values specified for the CAM-B3LYP functional?
>
> I would greatly appreciate any guidance or suggestions on correctly 
> configuring the CAM-B3LYP functional for this calculation. I attach my 
> input and output files.
>
> Thank you for your help!
>
> Best regards,
> Miguel
>

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