[Pw_forum] compatibility between pseudopotential choice and input_dft token

[Giuseppe Mattioli]

Dear Cristian

> Any combination is possible? Meaningful?

In my experience QE is (moderately) designed to let every user try his/her own DFT-like cake... Focusing on long range correlation, van der Waals et 
similia, there is some "wrong" physics you can avoid. For instance

> For example, can I safely set input_dft="vdw-df"
> and choose a LDA pseudo (say C.pz-vbc.UPF)?

LDA is known to overbind, and has been sometimes used as a "poor replacement" of vdW correlation (a horrible thing, in my opinion). Add a more correct 
scheme like VDWDF to such tendency could lead to... cold fusion? :-)

> Or a GGA (say C.pbe-mt_fhi.UPF in my case)

All the vdW corrections (semiempirical DFTD2 included, london=.true., in &system) are well tested with a given kind of xc functional. This is often 
discussed in the related papers. If you are not certain of the functional recipes, look into the funct.f90 file. But this is not a hard limit. You may 
build your own functional, including vdW. I've tested, with PBE pseudopotentials, an hybrid+vdW functional time ago ('sla+pw+hse+vdw1'), with good 
results on molecule-surface interactions.

HTH

Giuseppe

On Friday 05 April 2013 13:08:39 Cristian Degli Esposti Boschi wrote:
> Dear all,
> 
> in these days I am doing some basic attempts using
> the implementation of van der Waals interactions within QE,
> taking for example carbon-based systems.
> 
> My question is about the compatibility (both at the code
> level and even at the physical level, if the question is
> addressable in this forum) of the form chosen
> through the input_dft token on the one hand
> and of the actual pseudopotential file on the other hand.
> 
> Any combination is possible? Meaningful?
> 
> For example, can I safely set input_dft="vdw-df"
> and choose a LDA pseudo (say C.pz-vbc.UPF)?
> 
> Or a GGA (say C.pbe-mt_fhi.UPF in my case)?
> 
> The same with input_dft="vdw-df-c09" or
> "vdw-df2-c09" ?
> 
> Thanks in advance for any help. Have a nice weekend.
> 
> Cristian


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   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
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