[CPMD-list] Warning message in LSD calculation

[Axel Kohlmeyer]

On Fri, 27 May 2005, Hong Won Keon wrote:

HWK> Dear CPMD-lists,
HWK> 
HWK>  
HWK> 
HWK> I'm calculating C atom's lowest energy with LSD calculation
HWK> 
HWK> I've faced two problems.
HWK> 
HWK> One is the warning message like this "!!WARNING FROM DETDOF : WHY IS
HWK> GRIB LESS THAN UNITY!!"
HWK> 
HWK> What's wrong with this? And Is it a big problem? I mean, does it affect
HWK> the result seriously?

not at all. with a single atom in a periodic system, you have no 
degrees of freedom (DoF). some of the code in CPMD (being 
predominantly an MD code) compute properties, that are calculated per DoF
(by dividing through GLIB). now this warning will always be printed,
if CPMD internally forces GLIB to 1 so it does not crash because
of a division by zero later.

HWK> Two is for Carbon the orbital doesn't converge to 10-6, it takes long.
HWK> How can I manage to do this? 

LSD calculations always converge less easily than closed shell 
calculations. since you have to have a lot of vacuum in your
system, the convergence problems may be due to noise from
that area. especially for gradient corrected functionals, you have to 
tinker with GC-CUTOFF and perhaps also raising the plane wave cutoff
can help a little bit.

HWK> Is it ok to lessen the convergence criteria to 10-4? 

that fully depends, on what you want to do with the 
not-so-well converged result.

HWK> 
HWK> Or are there any other methods?

use a code with a local basis set. this is _much_ more 
suiteable for that kind of system.


regards,
	axel.
HWK> 
HWK>  
HWK> 
HWK> Thanks in advance,
HWK> 
HWK>  
HWK> 
HWK> HONG W.K. 
HWK> 
HWK>  
HWK> 
HWK> 

-- 

=======================================================================
Dr. Axel Kohlmeyer   e-mail: axel.kohlmeyer at theochem.ruhr-uni-bochum.de
Lehrstuhl fuer Theoretische Chemie          Phone: ++49 (0)234/32-26673
Ruhr-Universitaet Bochum - NC 03/53         Fax:   ++49 (0)234/32-14045
D-44780 Bochum  http://www.theochem.ruhr-uni-bochum.de/~axel.kohlmeyer/
=======================================================================
If you make something idiot-proof, the universe creates a better idiot.