[QE-developers] interpretation of avg # of iterations

[Ziang Zhang]

Dear developers,


In Quantum Espresso outputs, there are average # of iterationsprinted after
each SCF iteration.

  365      Self-consistent Calculation
  366
  367      iteration #  1     ecut=    45.00 Ry     beta= 0.40
  368      Davidson diagonalization with overlap
  369      ethr =  1.00E-02,  avg # of iterations =  2.0

I looked into the source code, the comment says the avg_iter is *H*psi
products*

```
PW/src/c_bands.f90

237  REAL(KIND=DP), INTENT(INOUT) :: avg_iter
238  !! average number of H*psi products

However, it seems to present the number of other loops inside a SCF
iteration:

PW/src/c_bands.f90

242  REAL(KIND=DP) :: cg_iter, ppcg_iter, rmm_iter
243  ! (weighted) number of iterations in Conjugate-Gradient
244  ! (weighted) number of iterations in RMM-DIIS

So, How do the *H*psi products *related to the average number of
iterations? How to interpret this number?


Thanks and regards,
*Ziang Zhang*

Ph.D. Student in Applied Physics
Computational Physics & Materials Science Lab
Physical Science and Engineering Division
3254-WS12, Building 3

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