[QE-users] Result precision across different builds

[Paolo Giannozzi]

On 8/28/26 03:52, Simon Michnowicz via users wrote:
> Dear User List
> I am helping a researcher install Quantum Espresso. I find different 
> combinations of compilers/libraries produce slightly different results 
> upon a sample input given to me. The researcher said the results should 
> be consistent up to 5 decimal points.  Is the  variation that I see to 
> be expected, or could there some other problem here?
> 
> Tool                                       Final Energy
> Intel Compiler,MKL               -314.1147158171
> gcc/15.2.0-gcc-11.5.0/MKL        -314.1256316418
> gcc/11.4/openblas                -314.1256341822

no, the difference between the first result and the two next is vastly 
larger than expected. But: what kind of calculation is this? in some 
cases (e.g., variable-cell calculations, DFT+U), small unavoidable 
numerical discrepancies may build up and lead to more significant 
differences in final results.

Paolo

> 
> much thanks
> 
> *---
> Simon Michnowicz *
> Senior Application Specialist, High-Performance Computing
> 
> *Monash eResearch Centre*
> Monash University
> 15 Innovation Walk, Building 75, Clayton Campus
> Wellington Road, VIC 3800
> Australia
> 
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> E: simon.michnowicz at monash.edu <mailto:simon.michnowicz at monash.edu>
> monash.edu <http://monash.edu/>
> 
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine Italy, +39-0432-558216