[QE-users] [SPAM] A problem about cell_dofree='ibrav'

[Paolo Giannozzi]

A quick glance at the code seems to indicate that
cell_dofree='ibrav+something'  is implemented only for BFGS minimization,
not for variable-cell molecular dynamics

Paolo

On Mon, Mar 7, 2022 at 5:14 PM Tianhua Wang via users <
users at lists.quantum-espresso.org> wrote:

> Dear Quantum ESPRESSO developers,
>   I am doing the cell optimization for cassiterite (SnO2) using the
> variable cell shape molecular dynamics (i.e., *cell_dynamics='damp-w'*)
> in QE 7.0. I had set *ibrav=6* for the crystal of cassiterite, and wanted
> to constrain *cell_dofree='ibrav+shape'* during the optimization.
> However, I found the none-zero values of v1_y&z, v2_x&z, v3_x&y in the
> output file, e.g.,
>
> *CELL_PARAMETERS (alat=  8.95238858)*
> *   0.999715701   0.000000089  -0.000000001*
> *   0.000000089   0.999715701  -0.000000001*
> *  -0.000000001  -0.000000001   0.672987836*
>
> which was not absolutely consistent with the initial ibrav choice (i.e.,
> *ibrav=6*). Then I tested the performance of *cell_dofree='ibrav'*, and
> found the same phenomenon. It seems that the *cell_dofree* command does
> not strictly constrain the initial ibrav choice. I also tested
> *cell_dofree='xyz+shape'* although I had guessed that it did not work.
>   I am wondering if there is any way to strictly achieve
> *cell_dofree='ibrav+shape'* (which is equal to *cell_dofree='xyz+shape'*
> in this case) during the cell optimization. Perhaps another solution is to
> fix the angles during the cell optimization, but how to achieve? My input
> file is attached for reference.
>   Thank you for your time and I am looking forward to your reply.
> Sincerely,
> Tianhua Wang
>
> ------------------------------
> Tianhua Wang
> State Key Laboratory for Mineral Deposits Research
> School of Earth Sciences and Engineering
> Nanjing University
> 163 Xianlin Avenue, Nanjing
> Jiangsu 210023, China
>
>
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 206, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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