[Pw_forum] Converting pseudopotentials from CPMD

[Paolo Giannozzi]

On Nov 25, 2011, at 17:02 , Merlin Meheut wrote:

> However, for the rest of the file, the CPMD file has only a &POTENTIAL
> field with 2S and 2P potentials, whereas the UPF file have <PP_RAB> ,
> <PP_LOCAL>, and <PP_NONLOCAL> fields, and I do not see any agreement
> between the two. What should be the connection?

the contents of the UPF file is documented (sort of) (but more than  
most other
file formats) here:
    http://www.quantum-espresso.org/wiki/index.php/ 
Unified_pseudopotential_format
UPF always assumes a fully nonlocal form. Most other file formats  
assume the
semilocal form. Transforming the latter into the former requires  
atomic (pseudo-)
orbitals and a choice for the local reference term (Kleinman-Bylander  
transformation).
Unless you use the Gauss-Hermite technique, you also need to choose a
local potential in CPMD (for light elements, l=1 is the typical  
choice). Of course,
the choice of the local potential affects the results, sometimes in  
catastrophic
ways.

> The cpmd file seems quite simple, with two wavefunctions, two  
> potentials
> and one nlcc field. Where is the difficulty of the conversion?

oh, nothing: trivial stuff. You just have to spend a few days chasing  
errors
before realizing that there is a missing 2 or r^2 or 1/r factor  
somewhere.
And don't count on documentation: reverse engineering is the only thing
that (sometimes) works.

I have recently used and extended the cpmd2upf converter. All  
improvements
are in the 4.3.2 version: more checks, more CPMD formats are recognized.
I am not aware of any major problem, but I haven't tried anything with
core corrections.

P.
---
Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222