[CPMD-list] NOSE Electrons and Quenching..

[Dave Sherman]

Dear all,

I'm still fuzzy about the best practice for  applying a thermostat to 
the electrons when doing CP molecular dynamics (on insulators..). The 
tutorial notes I've read suggest letting the system go without NOSE 
ELECTRONS, see what the Ekinc wants to be after, say, 100 steps, and 
thermostating  Ekinc to that value using NOSE ELECTRONS with a 
frequency (in cm-1)  ~ 3 times that of the highest nuclear vibration.  
Someone else in the CPMD list (I forgot who, sorry.. ), said that 
thermostating the electrons  is not necessary or even desired.  I'm 
also very confused about the desired value of EKINC.  For a system with 
50 H2O molecules and a few Na+ and Cl-'s, how high can EKINC be before 
I start worrying about leaving the BO surface?  If EKINC is too low, 
will the atomic nuclei move too fast and "lose their wavefunctions"?

Does it ever do any harm to quench the electrons back to the BO surface 
every so often during  "production
mode" of a dynamics run?  Would it be better to not use NOSE ELECTRONS 
and simply apply QUENCH BO ELECTRONS every 5000 or so timesteps?

Thanks for your help!

Dave Sherman

______________
David M. Sherman
Professor of Geochemistry
Department of Earth Sciences
University of Bristol
Bristol BS8 1RJ UNITED KINGDOM
Phone: 44-(0)117-954-5446
http://mineral.gly.bris.ac.uk