DFT+U with VdW

[Cyrille]

Dear all

I have noticed that VdW is disabled in DFT+U calculations. Is there a particular reason for this "limitation"?
I am presently doing calculations on molecular layers where DFT+U must be taken into account to describe properly the magnetic properties but the inter- and intra-molecular interaction probably needs to also include VdW.
What do you propose?

thanks in advance

Cyrille

[Jess Wellendorff]

Dear Cyrille. The main reason for this limitation is probably that it's not totally obvious that the fitted DFT-D parameters also work in the DFT+U case. But perhaps they will, and you can easily include a DFT-D2 or DFT-D3 correction by adding it to the LCAOCalcultor object by hand.

Simply combine the calculators from 2 scripts, one that uses DFT+U, and one that uses DFT-D. See attached script, which is straight from the VNL Scripter, except that I have manually added the DFT-D2 correction for PBE to the calculator:

correction_extension = GrimmeDFTD2(
    global_scale_factor=0.75,
    damping_factor=20.0,
    maximum_neighbour_distance=30.0*Ang,
    element_parameters={
        Carbon: [1.452*Ang, 1.75*J*nm**6/mol],
        },
    )

calculator = LCAOCalculator(
    basis_set=basis_set,
    exchange_correlation=exchange_correlation,
    numerical_accuracy_parameters=numerical_accuracy_parameters,
    correction_extension=correction_extension,
    )

[Cyrille]

OK thanks a lot. I will try it.
If I understand well: VNL does not allow DFT+U with VdW but it is possible to perform such calculation within atk.

Cyrille

[Jess Wellendorff]

Quite right: ATK can do GGA+U+vdW, but VNL does currently not allow you to set it up.