[Pw_forum] Applying vdW to only part of a system

[Giuseppe Mattioli]

Dear Ian

> I am thinking of examples where, for example, a vdW adlayer (e.g. benzene)
> sits on a surface, and surface doesn't need vdW corrections.

In my opinion, your premise is false. molecule-surface interactions  
generally *do need* vdW corrections very badly! You may say that  
DFT-D2 (vdw_corr='grimme-d2') overestimates vdW forces between  
molecules and transition metal or metal-containing surfaces. DFT-D3  
corrects such a behavior, but it is regretfully still not implemented  
in QE. However, I've obtained very good results by using one of the  
several ab initio vdw-df schemes, e.g. input_dft='vdw-df-c09'.

If you want to stick to vdw_corr='grimme-d2', then you may follow  
Evren's suggestion and you can tune (not suppress) the surface C6  
coefficients in order to avoid a too strong interaction between  
molecule and surface.
HTH
Giuseppe


Quoting Ian Shuttleworth <shuttleworth.ian at gmail.com>:

> Is it possible to apply vdW forces to only a part of system?
>
> I am thinking of examples where, for example, a vdW adlayer (e.g. benzene)
> sits on a surface, and surface doesn't need vdW corrections.
>
> If I add the vdw_corr toggle (or if I set an appropriate value
> to 'input_dft') I've understood that vdW are applied to the entire system -
> if this is right, how could I make this option more selective?
>
> With thanks
>
> Ian


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    Giuseppe Mattioli
    CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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