[Wien] Minimization stops by error

[Steven Homolya]

On Wed, 17 Sep 2003 05:43 am, Hu, Qing Miao wrote:
> I have used Wien2K to minimize the bond length of CO in a big box. The
> minimization scheme I used was BFGS and the command for the calculation
> was " min -j 'run_lapw' -I -fc 1.0 -i 40". However, after 18  steps of
> minimization , the program stoped by 'ERROR: ifnc>ipos'. Just before the
> calculation stoped, I have modified the delta parameters (from 0.3 to
> 0.05 and then to 0.1) according to the changes of the forces. Is the

Not sure about the ifnc>ipos, but I _suspect_ the delta's are not used for 
BFGS which uses quadratic interpolation to guess minimum E configuration. You 
probably started too far from equilibrium configuration (in which case BFGS 
will be unstable).

> error related to the modification? What do 'ifnc' and 'ipos' mean?  And,
> how to avoid this problem? Any answer will be greatly appreciated.
>

It would be easiest to do the optimisation "by hand". Just do several scf 
calcs. over a range of bond lengths centred on the experimental value. Then 
determine optimal value graphically from the E vs bond length data.

-- 
Steven Homolya
School of Physics and Materials Engineering
Monash University VIC 3800
Australia
Tel: INT +61 3 9905 3694
Fax: INT +61 3 9905 3637