[CPMD-list] Gold pseudopotentials and cell parameters

[Eduardo J. Lamas]

Dear Stefano:
              In the cpmd download are (contrib directory, file
pseudo_ext.tar.gz) there is a Au MT pseudopotential.
It is also nice because it has information about the reference states (one
for s and d channels and the other for the p channel) used to build it so
you can use Haman PP code in case you want to reproduce it.

If I were you I will use GAUSS-HERMIT=15 instead of KLEINMAN-BYLANDER for
the calculation of the non local part of the PP as it is in general
recommended for transition metals. 

Regards,

Eduardo

-----Original Message-----
From: cpmd-list-bounces at cpmd.org [mailto:cpmd-list-bounces at cpmd.org] On
Behalf Of Stefano Piana
Sent: Thursday, December 09, 2004 1:04 PM
To: cpmd-list at cpmd.org
Subject: [CPMD-list] Gold pseudopotentials and cell parameters


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 
Au+ 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

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