[Pw_forum] Relaxation giving negative relative coordinates. / Chris Heard

[Christopher Heard]

Dear Stefano,

thanks for the answer. I will do that.

Cheers,
Chris
________________________________________
From: pw_forum-bounces at pwscf.org [pw_forum-bounces at pwscf.org] On Behalf Of Stefano de Gironcoli [degironc at sissa.it]
Sent: 16 May 2011 12:13
To: PWSCF Forum
Subject: Re: [Pw_forum] Relaxation giving negative relative coordinates.

there is nothing strange in negative positions
anyway the system is periodic so you can remap them on the  positive
axes if you like,

stefano

On 05/16/2011 12:17 PM, Christopher Heard wrote:
> Hello,
>
> I am running QE for a small atomic cluster, in a single cubic unit cell, with the 'relax' keyword, just a simple local minimisation.
> The atomic coordinates are fractional coordinates of the unit cell, but the problem is that the output gives some negative values.
> I'm new to QE, so perhaps this is easily explained (if so, sorry), but it seems strange that the simulation would converge, and how does the code know what positions/energies negative values correspond to?
>
> -----------------------------------------------------------------------------------------------------------------
> INPUT
> &CONTROL
>       calculation  = "relax",
>       prefix       = "pwscf",
>       pseudo_dir   = ".",
>       outdir       = ".",
>       etot_conv_thr=  1.D-3,
>       forc_conv_thr=  1.D-2,
>       nstep        =  200,
> /
> &SYSTEM
>       ibrav        =  0,
>       nat          =  4,
>       ntyp         =  2,
>       ecutwfc      =  20.D0,
>       occupations  = "smearing",
>       smearing     = "mp",
>       degauss      =  0.6,
> /
> &ELECTRONS
>       electron_maxstep     =  100,
>       conv_thr     =  1.D-6,
>       mixing_beta  =  0.3,
> /
> &IONS
> /
> CELL_PARAMETERS cubic
>   6.70  0.00  0.00
>   0.00  6.70  0.00
>   0.00  0.00  6.70
> ATOMIC_SPECIES
> Cu   63.55  Cu.pbe-d-rrkjus.upf
> Ag  107.80  Ag.pbe-d-rrkjus.upf
> ATOMIC_POSITIONS {crystal}
>   Cu  3.352950000000000E-002  0.231848250000000       0.909548000000000
>   Cu  0.385636250000000       0.891478500000000       9.939174999999999E-002
>   Cu  0.205962500000000       0.843170750000000       0.568072500000000
>   Ag  0.109203000000000       5.366124999999999E-002  5.051524999999999E-002
> K_POINTS {Gamma}
> -----------------------------------------------------------------------------------------------------------------
>
>
> -----------------------------------------------------------------------------------------------------------------
> SAMPLE OF FINAL OUTPUT
>
>       the Fermi energy is    19.5731 ev
>
> !    total energy              =    -336.07301310 Ry
>       Harris-Foulkes estimate   =    -336.07301304 Ry
>       estimated scf accuracy<           2.4E-09 Ry
>
>       The total energy is the sum of the following terms:
>
>       one-electron contribution =     -15.71264533 Ry
>       hartree contribution      =      65.46190146 Ry
>       xc contribution           =     -55.48851306 Ry
>       ewald contribution        =    -330.01856694 Ry
>       - averaged Fock potential =       0.00000000 Ry
>       + Fock energy             =       0.00000000 Ry
>       smearing contrib. (-TS)   =      -0.31518923 Ry
>
>       convergence has been achieved in   6 iterations
>
>       Forces acting on atoms (Ry/au):
>
>       atom   1 type  1   force =    -0.00120005   -0.00208895   -0.00171136
>       atom   2 type  1   force =    -0.00716149   -0.00098208    0.00204276
>       atom   3 type  1   force =     0.00892231    0.00566633    0.00154815
>       atom   4 type  2   force =    -0.00056077   -0.00259530   -0.00187956
>
>       Total force =     0.013779     Total SCF correction =     0.000064
>
>       bfgs converged in  41 scf cycles and  30 bfgs steps
>       (criteria: energy<  0.10E-02, force<  0.10E-01)
>
>       End of BFGS Geometry Optimization
>
>       Final energy   =    -336.0730131033 Ry
> Begin final coordinates
>
> ATOMIC_POSITIONS (crystal)
> Cu      -0.050437709   0.504314433   0.629069336
> Cu       0.445520384   0.504573287   0.216995562
> Cu       0.419644090   1.004288078   0.669422976
> Ag      -0.080395515   0.006982952   0.112039626
> End final coordinates
>
> -----------------------------------------------------------------------------------------------------------------
>
>
> Many thanks,
> Chris
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