[CPMD-list] Gold pseudopotentials and cell parameters

[Stefano Piana]

Dear CPMD users,
I am still generating MT PBE gold pseudopotentials with not a lot of success 
so far.
At the moment I am able to generate pseudopotentials that give a reasonable 
geometry for the gold dimer but that have serious convergence problems when I 
try to simulate the bulk gold. I tried to generate the pseudos from the Au and 
Au+ atom, but they do not differ much. I tried with and without NLCC but, 
again, not much difference there.
I tried both LOC=S;P and D. LOC=S seems to give the best results. I also 
played a bit with the cutoff (from 50 to 80) and with the GC-CUTOFF (from 1e-6 
to 5e-5) but these do not seem to change things much, a cutoff of 50 and a 
GC-CUTOFF of 5e-6 seem to be reasonable.

Somebody suggested me that I should use a _LARGE_ number of K-Points for the 
bulk gold. Although I tried to run with up to 40 K-Points, I still have 
convergence problems and moreover it is not possible to optimize the cell with 
K-POints, therefore I cannot calculate the bulk properties of gold with my 
pseudo. An alternative is to use a bigger cell. I tried to run with 2x2x2 
supercell containing 32 gold atoms, but still convergence problems arise (i.e. 
the wavefunction never converges). I tried also INITIALIZE WAVEFUNCTION RANDOM 
and to run a few steps of PCG MINIMIZE before switching to ODIIS. The second 
method sometimes works, but convergence seems to be a bit erratic.

At the moment I am including only the 6S and 5D in the valence. IF I include 
the 5P as well I get very good results for the gold dimer (as expected from 
the literature), but the calculation is more expensive and it looks like the 
convergence problems for the solid state worsen.
I would like to have some suggestions. If anybody has already generated a MT 
pseudopotential for gold could he send it to me so that I can compare with my 
pseudos?

Stefano
-- 
Nanochemistry Research Institute
Curtin University of Technology
GPO Box U1987
Perth 6845 - Western Australia
tel. +61 8 9266 2687
piana at power.curtin.edu.au