[Pw_forum] London Dispersion force: DFT-D2

[Giuseppe Mattioli]

Dear Elliot
I do not know if I understand well your questions, but I try to answer:

> Could someone please assist me as to how to account for London
> dispersion forces with QE or essentially how to do a DFT-D2 calculation
> with the the aim of accounting for the energy contribution of dispersion
> forces.

Use vdw_corr='grimme-d2'
You will find in the output the dispersion force contribution to the total energy:

!    total energy              =   -2369.89004091 Ry
     Harris-Foulkes estimate   =   -2369.89004090 Ry
     estimated scf accuracy    <       0.00000001 Ry

     The total energy is the sum of the following terms:

     one-electron contribution =  -22567.16723495 Ry
     hartree contribution      =   11423.49753189 Ry
     xc contribution           =    -757.02966668 Ry
     ewald contribution        =    9530.66102736 Ry
     Dispersion Correction     =      -0.98373910 Ry
     Hubbard energy            =       1.13399751 Ry
     smearing contrib. (-TS)   =      -0.00195694 Ry

> I'm trying to account for  the energy contribution of London dispersion
> forces on the total energy of a hydrazine-nickel system.

Remember that DFT-D2 badly overestimate the interaction of molecules with metal surfaces, see Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A 
consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010, 
132, 154104. In cases such as N2H2 on Ni I would rather use vdwdf or vdwdf-c09 (see usage and related papers in QE documentation).

> ------------------------------
> &CONTROL
> tefield = .TRUE.,
>        dipfield = .TRUE.,
>        disk_io = 'low',
> 
> &SYSTEM
>        edir=3,
>        emaxpos=0.65,
>        eopreg=0.06,
>        eamp=0,
> ------------------------------
> 

This is a well tested but old and complex machine to correct the interaction of a dipole with its periodic replicas along z. I do not know if it is 
possible to estimate its impact on dispersion forces in a different way than by using/not using the dipole correction and check the difference between 
the above "Dispersion Correction" contribution to the total energy. However, I've satisfactorily used for a system similar to yours (thiol SAM on Au 
surface) this new setup (again, read the documentation and related papers), which decouple in a simpler way the dipole along z.

 &system
    input_dft='vdw-df-c09'
    assume_isolated = 'esm',
    esm_bc='bc1',
 /

HTH
Giuseppe


On Tuesday, May 03, 2016 12:41:49 AM Elliot Menkah wrote:
> Hi all,
> I'm trying to account for  the energy contribution of London dispersion
> forces on the total energy of a hydrazine-nickel system.
> 
> Could someone please assist me as to how to account for London
> dispersion forces with QE or essentially how to do a DFT-D2 calculation
> with the the aim of accounting for the energy contribution of dispersion
> forces.
> 
> When I correct the net-surface dipole on a system by using the variables
> and values below, does it affect the energy from dispersion forces, if
> so, how?
> How does correcting the net-surface dipole relate to accounting for
> dispersion forces?
> 
> ------------------------------
> &CONTROL
> tefield = .TRUE.,
>        dipfield = .TRUE.,
>        disk_io = 'low',
> 
> &SYSTEM
>        edir=3,
>        emaxpos=0.65,
>        eopreg=0.06,
>        eamp=0,
> ------------------------------
> 
> 
> I'm basically trying to account for London dispersion forces on a
> hydrazine-nickel system.
> Any info to help my computation would be gladly appreciated.
> Thank you
> 
> Kind Regards,
> Elliot

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   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
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