[CPMD-list] USPP: H_{2}O

[Christian Tuma]

Hello,

I observed the problem of poor convergence of the wavefunction in
BLYP calculations on isolated systems as well. Prof Hutter told
me that this may be due to Beckes gradient correction that involves
the calculation of \nabla \rho / \rho^(4/3). If both nominator and
denominator go close to zero the whole expression gets vague and
maybe heavily perturbed by numerical noise which is always present
in plane wave calculations.
That's why you could try to increase the parameter GC_CUTOFF as
recommended in the manual - especially when using USPPs.

Good luck,
Christian.

On Thu, Jul 03, 2003 at 04:36:19PM +0530, Dr. Balasubramanian Sundaram wrote:
... 
> We have tried several combinations of optimization schemes, but we are
> unable to converge the wavefunction to anything better than 7.0E-4
> (GEMAX).
> We tried even CONVERGENCE RELAX {5} option. 
... 
> &DFT
>   FUNCTIONAL BLYP 
> &END 
...
>

-- 
Christian Tuma             Humboldt-Universitaet Berlin
ct at chemie.hu-berlin.de     Arbeitsgruppe Quantenchemie (Prof. Sauer)
phone: +49-30-20937140     Brook-Taylor-Str. 2, 12489 Berlin, GERMANY
fax:   +49-30-20937136     http://www.chemie.hu-berlin.de/ag_sauer