I'm working on adsorption of a molecule, which vdW could play a crucial role. To incorporate vDW into the system VASP provides vDW correction estimates (IVDW), which include a whole range of estimation methods. However, I also saw some papers using functionals especially optB88-vdW.
Would anyone be able to explain what are the difference between these two approaches?
Additionally, I am using LREAL = Auto to speed up the system, it'd be great if you know whether this would have an impact on calculation with either of these methods?
Dear Thanaphong,
with the IVDW tag in VASP you can choose to apply a vdW correction, e.g. the Grimme correction. This is a kind of empirical vdW correction which in the end just adds an additional energy term accounting for vdW.
The optB88-vdW functional is a non-local exchange-correlation functional that directly accounts for dispersion interaction. I have not used optB88 but I assume it slows down the calculation.
Best, Holger
Dear Thanaphong and Holger
I've done calculations with pairwise corrections and vdW-DF (opt-PBE), and computational cost does not change that much. But make sure you have ''vdw_kernel.bindat'' in your calculation folder, otherwise it will take much longer.
Moreover, I think that vdw-DF is not formally implemented for spin polarized calculations. VASP makes an assumption to be able to run the calculation for spin-pol calculations, and this may lead to errors, so be careful with that. I have not tested it myself.
Good luck,
Oier.
Dear Holger and Oier,
For interactions between molecules, the different methods typically give qualitatively similar results. But the simpler IDW variants does not always work that well for some other systems, such as adsorption on metal surfaces.
Oier: There exists formal vdW-DF theory for spin-polarized systems (PRL. 115, 136402, 2015), but it has not made it into vasp yet, but exist in pwscf.
Cheers
Kristian
- Badges
- Science topic
- Similar topics
- Chemistry
- Theoretical Chemistry
- Computational Chemistry
- Molecular Dynamics