# Tag Info

14

Yes, vdW interaction affects energies but, also, geometries. This effect is the most pronounced if a DFT method predicts an interaction in a dimer to be repulsive: a geometry optimization will then simply dissociate the dimer. Normally, any vdW correction term does not only contribute energies, but als gradients, which in turn affect geometry optimizations (...

13

Dispersion correction DOES affect the final geometry. The dispersion interaction is a function of geometry. A crude approximation is to write the dispersion interaction between two neutral molecules as $$\Delta E_{\rm disp}(R)=-\frac{C_6}{R^6},$$ where $R$ the distance between the two entities. In some special case, like the system in which two rare gas ...

10

Optimization routines typically use the negative gradient of the energy in some form to determine the displacement during an optimization step and the dispersion correction changes the energy, which changes the gradient, and thus the optimization. You may get the same result in some cases but those are special cases, in general dispersion correction does ...

9

In computational chemistry, the term "van der Waals interaction" tend to refer to the London term only; the Keesom term (electrostatic interactions between two freely-rotating permanent dipoles) is generally included in the electrostatic interaction, while the Debye term (interaction between a permanent dipole and an induced dipole) is usually ...

9

Imagine you have a (hypothetical) method that can exactly capture the van der Waals interaction. Then when you do a geometry optimization, you are neglecting the quantum and thermal fluctuations of the atoms, and you end up with what is called the static lattice approximation. As quantum and thermal fluctuations tend to expand the lattice, then you would ...

8

Additive dispersion correction methods such as D3, D3(BJ), D3(BJ)+ATM, TS, MBD@rsSCS, etc. are good for geometry optimizations. These methods find the London dispersion interactions governed interlayer distance lower than the mean relative error of 2%. On the other hand, it's a good idea to avoid using these methods for energy calculations. For example, ...

7

tldr; Use dispersion correction for optimization I asked a very similar question a few years ago. Many indications for dispersion corrections in density functional methods are for intermolecular interactions. Clearly these corrections are important in such intermolecular or long-range interactions (e.g., inter-layer spacing in a material.. far from the ...

7

Van der Waal's radii for all atoms in the molecule are required to compute the dispersion for $\omega$B97X-D (this is also true for Grimme's dispersion). Unfortunately, Gaussian09 doesn't seem to have the radius for $\ce{Au}$ and it is also not possible to manually enter it through the input file. The radii for the elements up through $\ce{Rn}$ (atomic ...

3

@Xivi76 is correct. Dispersion corrections have no direct influence on the band structure. As such, there is no need to add the D3 correction on your HSE06 static calculation if you're only interested in the band structure. Nonetheless, some people include the D3 correction because the dispersion correction is basically free, and it's consistent with the use ...

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