[CP2K-user] [CP2K:22333] Re: Stabilizing/finding C2v-like Be_Ga acceptor state in CP2K HSE calculations

[Asif Billah]

Okay! I am looking at them.

Thank you!
Asif

On Monday, 20 July 2026 at 07:55:48 UTC-4 Johann Pototschnig wrote:

> There is the option to remain in the same space group:
> KEEP_SPACE_GROUP
>
> https://manual.cp2k.org/trunk/CP2K_INPUT/MOTION/GEO_OPT.html#CP2K_INPUT.MOTION.GEO_OPT.KEEP_SPACE_GROUP
> but they require a C2v space group to start with. 
>
> There are additional constrains possible, but for a 72 atom system, they 
> are not useful:
>
> https://manual.cp2k.org/cp2k-2024_2-branch/CP2K_INPUT/MOTION/CONSTRAINT.html
>
>
>
>
> On Saturday, July 18, 2026 at 3:27:10 PM UTC+2 Asif Billah wrote:
>
>> Hi CP2K community,
>>
>> I am studying Be substituting Ga in wurtzite GaN using CP2K/GPW with HSE 
>> + ADMM. 
>>
>> Based on previous resources, it is possible to obtain three different 
>> configurations for Be in GaN.
>> C3v: one long axial Be-N bond
>> pseudo-C3v: one long basal Be-N bond
>> C2v: distortion of the two adjacent acceptor-nitrogen bonds, not a single 
>> bond is significantly long
>>
>> I am trying to locate the shallow C2v like acceptor configuration, but so 
>> far my relaxations either converge to the deep C3v or pseudo-C3v polaronic 
>> states.
>>
>> I have already found stable/converged neutral C3v and pseudo-C3v 
>> branches. In the 72-atom cell at α = 0.335, the pseudo-C3v branch is with 
>> one long basal Be-N bond around 2.56 Å. The C3v branch has one long axial 
>> Be-N bond around 2.59 Å. These two states can be obtained easily where the 
>> initial structure will be by distorting the Be atom such that there will be 
>> a long basal or axial bond. 
>>
>> The shallow C2v state of Be_Ga acceptor results from the distortion of 
>> the two adjacent acceptor-nitrogen bonds, having the C2v symmetry of the 
>> atomic structure. The hole in this case is anisotropically delocalized in 
>> the (0001) wurtzite plane of GaN.
>>
>> Hence, for the C2v search, I am giving an initial structure by distorting 
>> the Be atom along a bisector direction involving the axial N neighbor and 
>> one basal N neighbor. However, it starts to collapse to the C3v/pseudo-C3v 
>> state.
>>
>> My question is: does anyone have advice on how to better initialize or 
>> constrain the search for the shallow C2v acceptor state in CP2K? Is it 
>> possible to obtain C2v state? In particular, I would appreciate suggestions 
>> on:
>>
>> 1. Better initial distortion pattern for C2v in wurtzite GaN
>> 2. Better spin/localization initialization for the hole
>> 3. Any CP2K-specific GEO_OPT/HSE/ADMM settings that help avoid collapse 
>> into C3v or pseudo-C3v
>>
>> Any guidance would be very helpful. Thank you!
>>
>> Ps:
>> My current setup is:
>>
>> System: Be_Ga in wurtzite GaN
>> Cell sizes tested: 72 atoms, moving to 108 and 300 atoms
>> Run type: GEO_OPT, fixed cell
>> Functional: HSE-style screened hybrid
>> alpha = 0.335
>> omega = 0.1058354422 bohr^-1   # approximately 0.2 Å^-1
>> MGRID cutoff = 600 Ry
>> REL_CUTOFF = 60 Ry
>> SCF: OT-CG, FULL_ALL preconditioner
>> q = 0: UKS TRUE, MULTIPLICITY 2
>> q = -1: UKS FALSE
>> HFX: four-center HFX + ADMM
>>
>> Basis/pseudopotential setup:
>>
>> Ga: DZVP-MOLOPT-PBE0-GTH-q13 + admm-dz-q13, GTH-PBE0-q13
>> N : DZVP-MOLOPT-PBE0-GTH-q5  + admm-dz-q5,  GTH-PBE0-q5
>> Be: DZVP-MOLOPT-PBE0-GTH-q4  + admm-dz-q4,  GTH-PBE0-q4
>>
>

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