[Pw_forum] Restarting PWSCF - usability issues

[sbraccia carlo]

Dear Kostya,

>  But I was arguing that storing *wfc* files is almost
> unnecessary in PWSCF since the wavefunctions could be
> rather trivially regenerated from the atomic guess and
> the old *.rho file.

restarting with atomic wfc usually implies that several iterations are needed 
to diagonalize the hamiltonian because the threshold is more strict than the 
one used for he first scf iteration of a "from_scratch" calculation.

Moreover, since there is no way for the code to know at restart time whether 
the starting potential is close to the scf one or not, the code doesn't know 
the correct value for diagonalization threshold. So the code supposes that 
the wfcs and the potential are "consistent" (at the same level of "self 
consistency").
If you are restarting the diagonalization with a rough estimate of the wfcs 
and with a potential close to self consistency, what will probably happens is 
that rho_out will be far from rho_in and the new potential will be also far 
from the "almost" scf one you were restarting from => some scf iteration will 
be needed to restore the "almost" scf potential.

> > > the program should understand the
> >
> > startingwfc=atomic
> >
> > > line even when a restart is requested
> >
> > doesn't it? not good
>
>  No, not good :-) 

This bug has been fixed in he CVS version and, probably, the fix will be 
contained in the forthcoming patch to version 2.0

carlo sbraccia