[Pw_forum] Energy convergence in a scf calculation

[Lorenzo Paulatto]

In data 14 settembre 2009 alle ore 17:42:47, Dimpy Sharma  
<dimpy.sharma at tyndall.ie> ha scritto:
>  ecutwfc=35Ry
>  ecutrho=120Ry
> So can anybody tell me why is it happening so?

Dear Dimpy,
your ecutrho is far too low! It should be at least 4 times ecutwfc (this  
is the default) and often much more (8-12 times) for ultrasoft  
calculations.

 From the documentation:

    +--------------------------------------------------------------------
    Variable:       ecutrho

    Type:           REAL
    Default:        4 * ecutwfc
    Description:    kinetic energy cutoff (Ry) for charge density and  
potential
                    If there are ultrasoft PP, a larger value than the  
default is
                    often desirable (ecutrho = 8 to 12 times ecutwfc,  
typically).
                    If all PP are norm-conserving, you should stick to the  
default;
                    you may reduce it to spare time, but not by a large  
amount.
    +--------------------------------------------------------------------


best regards

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Lorenzo Paulatto
SISSA  &  DEMOCRITOS (Trieste)
phone: +39 040 3787 511
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