[Pw_forum] Converged SCF total energies different in 6.0/6.1/6.2

[Lorenzo Paulatto]

 From Doc/release-notes

Fixed in 6.2 version

...
* Some constants in the definition of PBE functionals were truncated to
   6 significant digits. While not a bug, this could lead to tiny
   differences with respect to previous results and other XC
   implementations (r13592)


kind regards



On 21/12/17 03:11, WF wrote:
> Dear all,
> 
> In tests a normal DFT calculations with Si, I noticed that QE 6.0 and 
> 6.1 gives exactly same total energy with 6.0 and 6.1 (-15.75190880 Ry), 
> but with QE 6.2.1, the total energy is -15.75191309Ry. I tested this on 
> two different machines with different compilers, the results are the 
> same across all of them (at least to last digit). I did some tests on 
> larger systems also and found even larger difference. This 1e-5 Ry order 
> of difference is not negligible. Is there anything introduced in 6.2 
> leads to this difference? Thanks very much.
> 
> Best regards,
> 
> Feng
> 
> The input file is attached:
> 
> ====================
> 
> &control
> 
>      calculation='scf'
> 
>      outdir='./tmp'
> 
>      prefix='si'
> 
>      wf_collect = .true.,
> 
> /
> 
> &system
> 
>      ibrav=2,
> 
>      celldm(1) = 10.263,
> 
>      nat=2,
> 
>      ntyp= 1,
> 
>      ecutwfc = 40,
> 
> /
> 
> &electrons
> 
>      mixing_mode='plain'
> 
>      mixing_beta = 0.7,
> 
>      conv_thr =  1.0d-10,
> 
> /
> 
> ATOMIC_SPECIES
> 
> Si  1.0 Si_ONCV_PBE-1.1.upf
> 
> ATOMIC_POSITIONS {alat}
> 
> Si 0.00 0.00 0.00
> 
> Si 0.25 0.25 0.25
> 
> K_POINTS (automatic)
> 
> 4 4 4 0 0 0
> 
> ==============
> 
> --------------------------------------------------
> 
> Dr. Feng Wu
> 
> Postdoctoral researcher
> 
> Department of Chemistry and Biochemistry
> 
> University of California, Santa Cruz
> 
> Phone: 831-459-2874
> 
> 
> 
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-- 
Lorenzo Paulatto - Paris