Default value of mixing_gg0 is not suitable for water monomer system

[xuan112358]

Details

I recently discovered that the default value of mixing_gg0 was changed from 0 to 1 in the commit #3226 @WHUweiqingzhou . This causes the number of steps required for SCF iterative convergence to change from 9 to 25 in the example of calculating a single water molecule using PBE. This example is packaged below.
Does this mean that in some systems, this default value is not suitable?
github_mixing_gg0.zip

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[WHUweiqingzhou]

@xuan112358,
Yes, the default value is not good for some cases. I prefer let user modify these parameters as one wish since there is no default value which is good for all systems. Kerker precondition is very helpful for metal, but slow converge for some cases as you see.
Different software provide different default setting, like VASP open gg0 defaultly, while QE close it defaultly. If you have better idea, you can discuss here.

[xuan112358]

OK，I get it. Thanks for your help!