Global Scale Factor/ S6 value

[Dipankar Saha]

What will be the "Global Scale Factor/ S6" value in the case of the LDA functionals?? Is it taken as the same as 0.75 (GGA)??

[Anders Blom]

 

[Dipankar Saha]

Instead of GGA~PBE-D2+CP...if I use LDA~PW...then do BSSE CP correction and then do Dispersion correction using DFT-D2...
What should be the value of ..... S6  in "extendedCalculatorWithDFTD2(bsse_calculator, global_scale_factor= ? )"

[Umberto Martinez]

You can find a list to functionals for which the s6 scale factors have been determined in  S. Grimme, J. Comp. Chem. 27, 1787, 2006.
namely, 0.75 (PBE), 1.2 (BLYP), 1.05 (B-P86), 1.0 (TPSS), and 1.05 (B3LYP).

to my knowledge, this global scale factor has not been determined for LDA.

[Dipankar Saha]

Thank you Umberto....

 But I would like ask you another question....

If we do interfacing between two layers...maintain the distance as per the expmntl. data.... and use LDA-PW, then may be the binding energy value will be improper..../ But how the that will affect the nature of the band diagram, dispersion relation, stress etc. ??
To be more specific.... to get more accurate dispersion relation, BG, stress etc. .... which one is better (say, the inter-layer distance and, E_b are not the ONLY concerns)__
1) GGA~PBE-D2+CP  or,
2) LDA-PW with out DFT-D2 correction ......??

[Umberto Martinez]

These are corrections to the energy by adding extra terms.
They do not affect the electronic structure (besides giving you a different geometry) which is calculated by the DFT part (GGA or LDA in your case).

[Dipankar Saha]

"besides giving you a different geometry" ....means??

[Umberto Martinez]

means the electronic structure depends also on the geometry of your system.
grimme dispersion correction and CP correction may give you a different geometry (interlayer distance in your case) with respect to GGA/LDA only.

[Dipankar Saha]

Now suppose...

if  there are no stacked layers....thus no concept of vdW force...., then for finding the electronic band structure, as well as phonon dispersion....which one should we prefer...LDA-PW or GGA-PBE? Any comparative adv. or disadv. of GGA_PBE ??
(N.B. :- Again, here is no question of under estimating or overestimating the inter layer distance or, binding energy....as it's a mono layer)

[Anders Blom]

Why not just do both and compare, then you will know if there is a difference? That will be an interesting result to include in your paper. Do note however, that you may need a larger mesh cut-off for GGA for good accuracy.

[Dipankar Saha]

Dr. A. Blom,

Thank u for mentioning the point regarding the mesh cut-off for GGA....
...let me check...  

Regards__
Dipankar