[CP2K-user] [CP2K:21592] Clarification of R_CUTOFF in VDW_POTENTIAL

[Jürg Hutter]

Hi

CP2K does not use MIC for vdW corrections. You can specify any cutoff radius.
Atoms within 2*R_CUTOFF will interact. You can check the convergence of the vdW
energy by increasing the cutoff .

regards
JH

________________________________________
From: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of emerson p l <emersonp90 at gmail.com>
Sent: Thursday, June 26, 2025 9:41 PM
To: cp2k
Subject: [CP2K:21590] Clarification of R_CUTOFF in VDW_POTENTIAL

Dear cp2k community, I hope you’re all doing well.

I’m writing to ask for clarification on the choice of the cutoff radius R_CUTOFF​ parameter when using periodic boundary conditions in VDW_POTENTIAL in AIMD and geometry/cell optimizations:

      &VDW_POTENTIAL
         POTENTIAL_TYPE PAIR_POTENTIAL
         &PAIR_POTENTIAL
            PARAMETER_FILE_NAME dftd3.dat
            TYPE DFTD3
            REFERENCE_FUNCTIONAL PBE
            R_CUTOFF [angstrom] 10
         &END
      &END VDW_POTENTIAL

Suppose I have a cubic simulation box with side length L = 5 angstrom, and I (mistakenly) set R_CUTOFF​ = 10 angstrom. Would setting RCUTOFF​ = 10 angstrom in a 5 angstrom cubic box cause the cutoff sphere to extend beyond the primary cell and overlap with periodic images, resulting in unphysical, multiply-counted interactions?

My understanding from classical MD is that we must obey the minimum-image convention, which requires R_CUTOFF​ ≤ 2 Lmin​​. I don't know if R_CUTOFF has this physical meaning of classical MD.

Thank you very much for your time and insights.

Best,

Emerson


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