[CPMD-list] about oxygen Ultra-soft PP generated by USPP

[Axel Kohlmeyer]

On Mon, 2 Apr 2007, qfzhang wrote:

QZ> Hi, dear all!

dear qianfan zhang.

QZ>   I want to use USPP to generate the US-PP for oxygen in the
QZ> calculation of oxi de. But the result is not good in the oxide(even
QZ> I use very large supercell). I want to add l=2 channel in the O

first of all, if you don't tell us, what you are trying to do and
what your input looks like, i would strongly suspect that you are
doing something wrong, since the oxygen ultrasofts generated by 
bernd meyer _do_ work well with a large number of systems, even
oxides. so please provide some input that _proves_ that the 
pseudopotential is at fault. thanks.

QZ> US-PP, because I find that the TM-PP I used bef ore includes the d
QZ> channel.  But I find it is impossible for me to generate such a

you should be _very_ careful with that. pseudopotentials created
with the 'haman' style PP code that are in the cpmd pp library
mostly contain a unbound, bogus d channel, which will either have
little contribution (if used with LMAX=D LOC=P) or may give worse
results (if used with LMAX=D, which implies LOC=D).

QZ> US-PP.Is there anyone who know how to do that?

adding another projector to existing USPP inputs is actually
rather straightforward. just follow the instructions in the 
INPUT_XX files that ship with the code. the problem is to have 
it converged and bound. so you may have to slightly oxidize
the atom and/or shift some fractional occupation to the d-state.

QZ>   Or who know some tricks to improve the quality of US-PP?

before you put too much effort into optimizating the potential,
you may be better off to stick with a reasonable norm-conserving
pseudopotential. you avoid some of the overhead and 'only' need
some more cpus resources to distribute the work. but then again
with ultra-softs, CPMD usually does not scale that far, so in case
you have a large enough resource to run on, you may find NC-PPs 
about as efficient as US-PPs.

cheers,
   axel.


 
   Best wishes
                                                      Qianfan Zhang
                                                      2007-04-02



-- 
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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
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