The CASINO forum

Dear Eric, The DFT energy is not necessary for the generation of the pwfn/bwfn files, however it may point to some inconsistency in the way the routine is constructing the wave functions which are then written in these files. You may try to turn off the error message, but best would be to understand...

Dear Phil,

No, I don't have any evidence of the PP error being necessarily smaller in QMC.

Best wishes,

Dario

Dear Philip, In my view there are a few issues here: - you say there are large finite size effects in DFT too, but it is not clear if you are referring to k-point sampling of genuine H2-H2 interactions on the surface. Of course, the latter have nothing to do with QMC finite size effects, and so if y...

Dear Neil, I see. I do have an accumulated structure factor, but I am not quite sure how to use it in combination to Eq. 59. Of course, one way to addressing the issue could be to pretend to have a 3D system and use the 3D correction, which indeed seems to work quite well. I am always a bit wary abo...

Dear Neil, thanks for this. Casino only computes the KE correction in 2D, does it mean that the formulae for the XC correction are not implemented ?
Using scaling law is difficult if you can only afford a very limited number of different sizes.

Dario

What do we mean that in 2D finite size corrections are purely kinetic ? Is it really so, or casino can only deal with dKE in 2D systems ?

dbarrc=10:

Time taken in block : : : 3311.0801

no dbarrc set in input file:

Time taken in block : : : 178.8800

you are a genius!

I am doing a calculation on a cell containing 96 hydrogen atoms and one twist. If I use complex_wf=F (the default) or complex_wf=T I get the same energy (as expected) and CASINO also runs at roughly the same speed. If I now repeat this very same set of calculations, but using a larger 784 atoms cell...

maybe, but you don't know how small is small enough. Often you find that it looks linear in some range, then you keep decreasing the time step and find that it departs from the linearity that you thought you were observing.

Extrapolations are always dangerous, as we do not know what is the functional form of the energy as function of time step.