[Wien] DFTD3 h-BN testing

[Tristan de Boer]

Hi,
I've installed DFTD3 and am attempting to make sure it's installed 
correctly, so I've been attempting to reproduce slide 20 of F. Tran's 
2015 WIEN2k workshop. Are the cells in this slide held to a constant 
volume as the interlayer distance is changed, or is the unit cell volume 
changing as well? I've tried calculations with the PBE functional both 
ways, with and without DFTD3, I can't reproduce this figure.

If I hold the volume constant and change the interlayer spacing, I get 
something resembling the PBE+D3 line in total energy, with and without 
DFTD3 (assuming :ENE = :ENE(no dispersion corrections) + :EDFTD3). If I 
simply change the interlayer spacing I get a monotonic decrease in total 
unit cell energy with increasing spacing without the minimum shown in 
the slide both with and without :EDFTD3. For both cases, :EDFTD3 is 
about -0.03 -- -0.04 Ry.

Alternatively, since :EDFTD3 matches the output in case.scfdftd3, should 
I simply ignore the issue and assume things are working well?
Regards,
Tristan