Are you sure that PBE (or any GGA-like functional) works well for your
case? Is this a case in which a hole localises on a bond? GGA may tend
to favor configurations in which the hole is uniformly spread, due to
self-interaction errors. I encountered a similar case many years ago (Al
defect in SiO2), wrote a paper with wrong results :-( and have been more
careful with GGA since
Paolo
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Hello everyone,
I am currently studying a supercell composed of 510 silicon atoms,
including a divacancy. I am conducting a relaxation calculation using
the PBE pseudopotential. Since silicon is tetravalent, each divacancy
causes three neighboring silicon atoms to lose a bond. At a total charge
of 0, I anticipate two distinct equilibrium structures.
1. The three silicon atoms form two bonds, resulting in two short
distances (~3 Å) and one longer distance (~3.5 Å) between them.
2. The three silicon atoms form only one bond, leading to one short
distance and two longer distances between them.
To achieve these two structures, I initialize the relaxation calculation
by adjusting the distances between the three atoms to resemble the
expected configurations. To expedite the calculation, I perform the
relaxation in two stages: the first with force convergence (forc_conv)
set to 10−310^{-3}10−3 and a wavefunction cutoff energy (ecutwfc) of 10
Ry, and the second with forc_conv set to 10−410^{-4}10−4 and ecutwfc of
25 Ry.
However, despite trying various approaches, I consistently observe three
long distances of approximately 3.4 Å at the end of the second
relaxation step, even though the structure appears correct after the
first step.
Has anyone encountered a similar issue? Any suggestions on how to
resolve this problem would be greatly appreciated.
Thank you.
Best regards,
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--
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 206, 33100 Udine Italy, +39-0432-558216
X SCUOLA ENERGIE RINNOVABILI 16-21/9/2024 - PRE-ISCRIZIONE
https://agenda.infn.it/event/39573/
_______________________________________________
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 [email protected]
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