[CPMD-list] question about the optimalization of cell parameter

[Ari.P.Seitsonen at iki.fi]

Dear Imre,


> I tried to optimize the Si lattize use the following input file
> &CPMD
> OPTIMIZE GEOMETRY
> RESTART WAVEFUNCTION COORDINATES LATEST
> SPLINE POINTS
>   5000
> CONVERGENCE CELL
> 0.1
> &END
> &DFT
> FUNCTIONAL PZ
> &END
>  &SYSTEM
> SYMMETRY
>   2
>   CELL
>  10.2612 1.0 1.0 0.0 0.0 0.0
>    CUTOFF
>    36.
> KPOINTS MONKHORST-PACK
>  4 4 4
> STATES
> 4
> POINT GROUP
>   AUTO
> TESR
>   4 4 4
> SCALED
>  &END
> &ATOMS
> *Si_SG_LDA KLEINMAN-BYLANDER
>   LMAX=D
>    2
>    0.00  0.00  0.00
>    0.25  0.25  0.25
> &END

> After the second iteration I got the following answer
> ATOM          COORDINATES                GRADIENTS
>    1 Si  0.0000  0.0000  0.0000   0.000E+00  0.000E+00  0.000E+00
>    2 Si -2.5653  2.5653  2.5653   0.000E+00  0.000E+00  0.000E+00
>  ****************************************************************
>  *** TOTAL STEP NR.     2           GEOMETRY STEP NR.      1  ***
>  *** GNMAX=  0.000000E+00                ETOT=     -7.923217  ***
>  *** GNORM=  0.000000E+00               DETOT=     0.000E+00  ***
>  *** CNSTR=  0.000000E+00                TCPU=          0.73  ***
>  ****************************************************************
>  ================================================================
>  =              END OF GEOMETRY OPTIMIZATION                    =
>  ================================================================
> Can you explain somebody me this behaviour?

Hmm, everything seems to go fine, or? In bulk silicon there are no
geometrical degrees of freedom to be optimised, so "OPTIMISE GEOMETRY"
doesn't make sense (i.e. doesn't do anything), and the optimisation
stops when it notices that the energy doesn't change at all (as the
atoms didn't move). Or did I misunderstand something? Did you want to
relax the lattice constant also? This most likely doesn't work with
the k points, but someone please correct me if this is not true.

    Greetings,

       apsi

-- 
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 Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
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