grimmedisp
This keyword specifies the use of Grimme’s third-generation dispersion correction (DFT-D3).
Options
Always enable DFT-D3 in DFT calculations—especially for systems held together by weak interactions. In practice, it is advisable to apply it in all cases.
If the input file omits the grimmedisp keyword, no DFT-D3 correction is applied.
type
| Value | bj Becke–Johnson–damped DFT-D3 (DFT-D3(BJ)). |
zero Zero-damping DFT-D3 (DFT-D3(0)). |
|
| Default | None |
You must choose either bj or zero; there is no default value.
The bj form usually performs better, but some functionals—such as M06, M06-2X, and M06-HF—are parametrised only for the zero form.
three_body
The optional three-body switch adds the Axilrod–Teller–Muto three-body dispersion term, which can be beneficial for large systems.
tz
When triple-zeta (or larger) basis sets are used, including the three-body term often yields additional accuracy.
Theoretical Background
The DFT-D3 method is a dispersion correction applied to DFT energies. It is based on the pairwise summation of damped dispersion terms. In modern DFT calculations, including the DFT-D3 correction is almost always beneficial; therefore, it is recommended for all calculations.
Input Examples
Examples: Weak Interactions in CH4-C2H6
This example illustrates the importance of applying the DFT-D3 correction when evaluating weak interactions. Both CH4 and C2H6 are non-polar, so the interaction between them is extremely weak. We assess this interaction using the EDA method at the B3LYP-D3(BJ)/def2-SVP level of theory:
mol
C -0.99275967 0.12491197 0.13574919
H -1.00662206 -0.95659619 0.18835421
H -0.34007185 0.51620582 0.90571860
H -0.63121516 0.43418579 -0.83650623
H -1.99486438 0.50482451 0.28603834
C 2.95955795 -0.58352084 -0.35430634
H 3.53618084 -1.49857448 -0.47007336
H 3.33520181 -0.05007297 0.51638813
C 3.07143559 0.28355041 -1.59942759
H 1.92316063 -0.85399112 -0.16804950
H 4.10875722 0.55492780 -1.78655076
H 2.69486480 -0.24574724 -2.47236370
H 2.49506428 1.19877654 -1.48025100
end
basis
def2-svp
end
scf
charge 0
spin2p1 1
type U # For EDA, this must be set explicitly.
end
grimmedisp
type bj
end
eda
type tso
frag 0 1 1-5 # Define CH4.
frag 0 1 6-13 # Define C2H6.
end
task
eda b3lyp
endThe output is as follows:
WITH BSSE correction:
Electrostatic interaction energy: -0.13 kcal/mol
Exchange-correlation interaction energy: 0.48 kcal/mol
Polarization interaction energy: -0.00 kcal/mol
Charge transfer interaction energy: -0.11 kcal/mol
Grimme s dispersion interaction: -0.87 kcal/mol
----------------------------------------------------------------
Total interaction energy: -0.62 kcal/mol
Thus, the interaction energy between CH4 and C2H6 is −0.62 kcal mol−1.
The dispersion component is −0.87 kcal mol−1, making it the dominant contribution.
Without the DFT-D3 correction, the interaction energy would be
−0.62 − (−0.87) = +0.25 kcal mol−1; in other words, the complex would be unbound.
This represents a quantitative error in the interaction energy.
Always include DFT-D3 in your DFT calculations.