[CP2K-user] Omega parameter in range-separated functionals

ZC Wong chm... at nus.edu.sg
Tue Jan 7 07:53:22 UTC 2020

Dear CP2K users,

I am interested in using the LC-wPBE functional in CP2K with a different 
value of omega from the original functional.
However, my test results in CP2K turned out to be quite different to those 
obtained using another program when I changed the value of omega.

Using the default value of omega for LC-wPBE (0.4), I obtained SCF energies 
of water as:
CP2K:               -76.41700469511423
Other program: -76.41700042778284
(Basis set: cc-pVTZ, taken from the Basis Set Exchange for CP2K)

That's OK. But when I changed the value of omega to 0.3 for both, my water 
energies differ significantly:
CP2K:               -75.96879714659988
Other program: -76.40681085213058

Then, I tried to reproduce some of the results from this paper 
(pubs.acs.org/doi/10.1021/acs.jctc.5b00820) using CP2K (LC-wPBE, 

HOMO/LUMO energies of uracil (eV):
>From the paper: -9.62 and 0.51
CP2K:                -8.79 and 1.34
Other program:  -9.51 and 0.67
(I used the cc-pVTZ basis set in CP2K and the other program again.)

Hence, I think I could be doing something wrong with the omega parameters 
in CP2K?

More details:
I compiled CP2K 6.1.0 using the toolchain; that uses Libxc version 4.0.3. 
All regtests passed without any errors after compilation.

This is the relevant section of my CP2K input file under DFT:

        &END LIBXC
          OMEGA 0.4000
          SCALE_COULOMB 0.0
          SCALE_LONGRANGE 1.0
        FRACTION 1.0
      &END HF
    &END XC

My input files are attached as well.

Thanks for any help or suggestions!

Zi Cheng
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