[QE-users] Symmetry dependent convergence

[Franklin T Cerasoli]

Hello,

I've been using QE for several years and recently came across an interesting issue when try to converge certain large systems.

Attached is a link to an inputfile for a 216 atom system. With QE-6.8 (also tested on v6.3), the structure converges only if nosym=.f. and noinv=.f.. There are two symmetry operations found, the identity and inversion.

Setting nosym=.t. causes the estimated scf accuracy to thrash around in the hundreds of thousands of Ry, while nosym=.f. allows strong convergence (1e-6 Ry) within 30 iterations.

Pseudopotentials are all pslibrary PBE. Below is a link to the inputfile and relevant parts of the scf output.

I would appreciate any advice for understanding what the heck is going on here.

-Frank Cerasoli
UC Davis Department of Chemistry

From the outputs:

With nosym=.f.
     Program PWSCF v.6.8 starts on  4Apr2022 at 16:30:24
...
      2 Sym. Ops., with inversion, found
...
     iteration #  1     ecut=    41.00 Ry     beta= 0.10
...
     total energy              =  -84091.83957606 Ry
     estimated scf accuracy    <       7.57588335 Ry
...
     iteration #  2     ecut=    41.00 Ry     beta= 0.10
     total energy              =  -84090.73018546 Ry
     estimated scf accuracy    <       5.24675479 Ry

     iteration #  3     ecut=    41.00 Ry     beta= 0.10
...
     total energy              =  -84091.16546184 Ry
     estimated scf accuracy    <       0.84010802 Ry


With nosym=.t.
     Program PWSCF v.6.8 starts on  4Apr2022 at 18: 9:20
...
     No symmetry found
...
     iteration #  1     ecut=    41.00 Ry     beta= 0.10
...
     total energy              =  -83948.30076200 Ry
     estimated scf accuracy    <  364559.66452101 Ry

     iteration #  2     ecut=    41.00 Ry     beta= 0.10
...
     total energy              =  -84392.52517827 Ry
     estimated scf accuracy    <  209530.42525106 Ry

     iteration #  3     ecut=    41.00 Ry     beta= 0.10
...​
     total energy              =  -85690.00953396 Ry
     estimated scf accuracy    <  338759.15202062 Ry


And the inputfile is here:
https://drive.google.com/file/d/1jaF7drV996sg4ckxYunyHPpE79SRDdjZ/view?usp=sharing

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