[CPMD-list] Choose potential type

[Axel Kohlmeyer]

On Tue, 22 Feb 2005, Axel Klix wrote:

AK> Dear All,

dear axel,
 
AK> I've been using cpmd for a while, but I'm still confused about how to 
AK> select a pseudopotential type (Goedecker etc.). What makes one choose 
AK> say a Goedecker potential instead of a Vanderbilt potential? (I 
AK> understand that Vanderbilt potentials allow a lower cutoff.) I hope I 
AK> didn't miss something obvious here :)

well, there are two main problems with using vanderbilt uspps
(in CPMD). the first is that only a limited subset of the functionality
in CPMD works with uspps (MD, wavefunction/geometry optimization and
related stuff and only at the gamma point and you have to make sure, that 
your real space grid is tight enough).
the second is that due to sacrificing norm-conservance for softer
pseudopotentials, your wavefunction has very limited meaning, so 
that not all features available for norm-conserving pseudopotentials
can actually be easily implemented or implemented at all. 

goedecker type potentials are generally very transferable, but need
high to extremely high plane wave cutoffs and are not so easy to
generate. troullier-martins pseudopotentials are somewhat in the middle.
they usually require a smaller cutoff than the goedeckers, but for
some elements, they can become tricky (e.g. d-metals) to make them
work correctly.

best regards,
	axel.

AK> 
AK> Best regards,
AK> Axel
AK> 
AK> 
AK> 
AK> 

-- 

=======================================================================
Dr. Axel Kohlmeyer   e-mail: axel.kohlmeyer at theochem.ruhr-uni-bochum.de
Lehrstuhl fuer Theoretische Chemie          Phone: ++49 (0)234/32-26673
Ruhr-Universitaet Bochum - NC 03/53         Fax:   ++49 (0)234/32-14045
D-44780 Bochum  http://www.theochem.ruhr-uni-bochum.de/~axel.kohlmeyer/
=======================================================================
If you make something idiot-proof, the universe creates a better idiot.