[QE-users] SCF energy rise up from iteration 2

[Rameswar Bhattacharjee]

Hi Paolo,
Thank you very much for your reply and suggestion. It looks strange to me
as the energy eventually converges to a high value (~0.06 Ry higher)
compared to the first iteration energy. One more thing I found unusual is
that (as I mentioned earlier) the total energy obtained at the gamma point
is ~0.07 Ry higher than the total energy at any other k-points. I am not
much experienced with periodic calculation and never had such experience
with finite methods.

Rameswar

On Tue, Dec 20, 2022 at 11:28 AM Paolo Giannozzi <paolo.giannozzi at uniud.it>
wrote:

> The energy is variational, that is: it goes down as self-consistency is
> approached. The energy term that makes the energy variational is however
> approximate and becomes exact only at self-consistency. As a consequence
> it may happen that at the beginning of the self-consistency the energy
> goes up instead of going down. Nothing to worry about as long as the
> energy eventually converges (monotonically from above)
>
> Paolo
>
> On 18/12/2022 19:23, Rameswar Bhattacharjee wrote:
> >
> > You don't often get email from rb1820 at georgetown.edu. Learn why this is
> > important <https://aka.ms/LearnAboutSenderIdentification>
> >
> >
> > Hi Everyone,
> > I am doing a single-point calculation on a 1D polymer in QE using
> > PBE-PAW. However, I am seeing an issue in the SCF iteration cycles. The
> > first iteration seems to print the right electronic energy but from
> > iteration 2 the energy suddenly increases significantly and then the SCF
> > ends up with higher energy. I am a little confused about how to
> > stabilize the SCF iteration so the energy does not go up. Any
> > suggestions will be highly appreciated.
> >
> > I am providing the output of the first three iterations of the SCF for
> > deep insights.
> >
> >
> ------------------------------------------------------------------------------
> >
> > iteration #1 ecut= 120.00 Ry beta= 0.30
> >
> > Davidson diagonalization with overlap
> >
> > ethr =1.00E-02,avg # of iterations =2.0
> >
> >
> > negative rho (up, down):1.348E-04 0.000E+00
> >
> >
> > total cpu time spent up to now is 13.7 secs
> >
> >
> > total energy=-304.41586797 Ry
> >
> > estimated scf accuracy< 2.72932626 Ry
> >
> >
> > iteration #2 ecut= 120.00 Ry beta= 0.30
> >
> > Davidson diagonalization with overlap
> >
> > ethr =3.79E-03,avg # of iterations =1.0
> >
> >
> > negative rho (up, down):1.006E-04 0.000E+00
> >
> >
> > total cpu time spent up to now is 16.3 secs
> >
> >
> > total energy=-304.13553253 Ry
> >
> > estimated scf accuracy< 0.76532583 Ry
> >
> >
> > iteration #3 ecut= 120.00 Ry beta= 0.30
> >
> > Davidson diagonalization with overlap
> >
> > ethr =1.06E-03,avg # of iterations =6.0
> >
> >
> > negative rho (up, down):5.328E-05 0.000E+00
> >
> >
> > total cpu time spent up to now is 19.4 secs
> >
> >
> > total energy=-304.26340272 Ry
> >
> > estimated scf accuracy< 0.08826578 Ry
> >
> >
> --------------------------------------------------------------------------------------------
> >
> > Thanks
> > Rameswar Bhattacharjee
> > Georgetown University
> >
> > _______________________________________________
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> --
> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> Univ. Udine, via delle Scienze 206, 33100 Udine Italy, +39-0432-558216
>
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