[Pw_forum] PAW in 4.0CVS3

[Chao Cao]

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Axel Kohlmeyer wrote:
> On Wed, 16 Apr 2008, Chao Cao wrote:
> 
> Dear Lorenzo,
>   Is there any major change or bug fix for PAW method between CVS2 and
> CVS3? I used exactly the same set of PP-generation input and PW input,
> but somehow got very different result in total energy and force (differs
> by several eV).
> 
>> lorenzo is probably (hopefully) asleep, so i'll give it a shot...
> 
>> the fundamental constants and unit conversions were updated to the 
>> latest CODATA 2006 recommended values. if you enter data that needs
>> to be converted to internal units, e.g. coodinates or cell dimensions
>> in angstrom, that may have the effect that you see.

Well, that IS the problem that I actually have no unit conversion,
unless "bohr" is also changed...:p


And about the discrepancy between SCF/relaxation, I was giving an easy
example since everyone has Cu/O PAW data in distribution. I have a case
that gives me ~0.1 eV difference, which makes me very uncomfortable...



Chao Cao

> 
>> i've seen even larger discrepancies in some cases where the code
>> (not QE) was even further off. makes you think about the real
>> accuracy of what we are doing here, don't it?
> 
>> cheers,
>>   axel.
> 
> 
>   Also, if I do structural relaxation using PAW in 4.0cvs3, and use the
> relaxed structure to do another SCF, the total energy/stress/force from
> SCF calculation can be substantially different from the final step in
> structural relaxation calculation. For example, I used the PAW dataset
> provided in pseudo/ directory to calculate Cu2O bulk, and the last step
> of relaxation gives me a total energy of -592.22777692 Ry and P=-0.03
> kbar; but if I start from the final structure and do one SCF, the result
> is -592.22732012 Ry and P=-0.42 kbar. Since I set conv_thr to be 1.0d-7,
> a 0.0004 Ry difference in total energy looks really big to me...
> 
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- --
Chao Cao

Quantum Theory Project and Department of Physics
University of Florida, Gainesville, FL 32611
U.S.A.
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