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I have done convergence testing for MoS2 (2x2x1) monolayer structure in the following order:

  1. ecutwfc
  2. ecutrho
  3. k_points

After setting these values, I would like to include vdW correction to the system using DFT-D.

My question: should I repeat the convergence testing for the above mentioned parameters?

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1 Answer 1

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In general, the answer is no.

The convergence steps you have taken allow you to obtain electronic structure and electronic energies at your desired precision. Many dispersion corrections (like Grimme's D3/D4 models) are additive and are not based on the electronic structure (only on geometry), and thus will be unaffected by it.

Some additive corrections, like the MBD and XDM models, compute atom dispersion coefficients from the electron density and will, in principle, be affected by the quality of the electronic structure. The use of van der Waals functionals, like vdW-DF or VV10, even entails switching the calculation to a different DFT functional outright (strictly speaking). However, in any of these cases, I would assume that a sufficiently converged electronic density from the base functional, will likely be good enough for a vdW treatment. At least, I have not seen a literature report where "good" settings for plain DFT were insufficient for such methods.

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