[Pw_forum] Fwd: Basic Relax Calculation issues

[Paolo Giannozzi]

If forces are zero by symmetry, there is nothing to relax

P.

On Fri, 2014-02-28 at 13:06 +0800, Zarah Baiyee wrote:
> Hi All, 
> 
> 
> I am a new user to Quantum Espresso, therefore this may be a bit
> trivial but I any help would be very welcome. 
> 
> 
> I am attempting a relax calculation using espresso version 5.0.2, for
> the geometry optimisation of a perovskite structure. For the input
> below, the calculation runs, however does not compute any forces and
> convergence without geometry optimisation to the original structure,
> with 0 bfgs steps. I am able to perform an expected relaxation if
> alter the initial atomic positions to asymmetric: (i.e.)  an oxygen
> molecule from:  O (0.500  0.5  0.0) to O(0.499 0.5 0.0). 
> 
> 
> Please may someone shed some light on to why this is the case, and if
> there is anything wrong with my input.  
> 
> 
> Thanks
> 
> 
> Zarah
> Zbaiyee at gmail.com
> 
> 
> &CONTROL
>   calculation  = "relax",
>   prefix       = "CO",
>   pseudo_dir   = "/Users/zarahbaiyee/espresso-5.0.2/pseudo",
>   outdir       = "/Users/zarahbaiyee/tmp",
>   forc_conv_thr = 1.0D-5
> /
> &SYSTEM
>   ibrav     = 0,
>   nat       = 5,
>   ntyp      = 3,
>   ecutwfc   = 60,
>   ecutrho   = 420,
> /
> &ELECTRONS
>   conv_thr    = 1.D-7,
>   mixing_beta = 0.7D0,
>   electron_maxstep = 400
> /
> &IONS
> /
> CELL_PARAMETERS bohr
>  7.60  0.0  0.0
>  0.0  7.60  0.0
>  0.0  0.0  7.60
> ATOMIC_SPECIES
>  Ba  137.32 Ba.pbe-mt_fhi.UPF
>  Fe  55.84 Fe.pbe-mt_fhi.UPF
>  O   15.99 O.pbe-kjpaw.UPF
> ATOMIC_POSITIONS {crystal}
> Ba  0.000  0.0  0.0  0 0 0 
> Fe  0.500  0.5  0.5
> O   0.000  0.5  0.5
> O   0.500  0.0  0.5
> O   0.500  0.5  0.0
> 
> K_POINTS {automatic}
> 9 9 9 0 0 0
> 
> 
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-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222