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

Tue Dec 20 18:22:57 CET 2022

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> 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>
> wrote:
>
> 
> *CAUTION:* This e-mail originated outside the University of Southampton.
> 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
>>
> _______________________________________________
> The Quantum ESPRESSO community stands by the Ukrainian
> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
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> _______________________________________________
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>
> _______________________________________________
> The Quantum ESPRESSO community stands by the Ukrainian
> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
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