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

[Tom Demeyere]

Hard to say without having a look at your system. If your system is a molecule in a (large) box then Gamma point might be enough. If you have a periodic system then you should perform a convergence test to be sure that your property of interest converge vs the number of k-points.

On 20 Dec 2022, at 18:23, Rameswar Bhattacharjee <rb1820 at georgetown.edu> wrote:


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Thank you, Tom. In that case, is the gamma point the best choice for me?

On Tue, Dec 20, 2022 at 12:17 PM Tom Demeyere via users <users at lists.quantum-espresso.org<mailto:users at lists.quantum-espresso.org>> wrote:
In periodic codes, properties (total energy is one of them) are averaged over the Brillouin zone. As a results you can’t do any assumption on how this property will change when you change k-points, it may sometime increase or sometime decrease, I don’t think this is unusual.

On 20 Dec 2022, at 17:37, Rameswar Bhattacharjee <rb1820 at georgetown.edu<mailto:rb1820 at georgetown.edu>> wrote:


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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<mailto: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:
>
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> 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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--
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Univ. Udine, via delle Scienze 206, 33100 Udine Italy, +39-0432-558216
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