[CPMD-list] path integral: normal & staging modes; electron thermostat

[Axel Kohlmeyer]

On Fri, 22 Jul 2005, Lan-Feng Yuan (lyuan at Princeton.EDU) wrote:

hi,

LY> &CPMD
LY>  CENTER MOLECULE
LY>  ISOLATED MOLECULE
LY>  MOLECULAR DYNAMICS
LY>  PATH INTEGRAL
LY>  CONVERGENCE ORBITALS
LY>   1.d-6
LY>  EMASS
LY>   340.0
LY>  TIMESTEP
LY>   5.

that is a pretty large time step for your choice
of fictitious electron mass. especially when starting
the PI-md and until you have reached equilibrium, you
may want to use a smaller time step.

LY>  NOSE IONS MASSIVE
LY>   300.0  2000.0
LY>  NOSE PARAMETER
LY>   4 0 0 6. 7 4

you also need to use a thermostat for the electrons.
on a single water molecule with a normal CP dynamics
i have been using something like:

NOSE ELECTRONS 
 0.00015  15000.0

there is an option CLASSICAL TEST (&CPMD section) which 
may help you figuring out the optimal value.

as far as i understood it - and i am no expert on PI-MD
so if somebody knows better, please correct me -
you have to keep the balance between the two thermostats
to get useful results. you will have a small but continous 
transfer of energy from the 'cores' to the fictitious electron 
dynamics, that you have to counter with both thermostats.
since you cannot run without thermostats, it is quite
tricky to figure out the optimal parameters...

best regards,
	axel.

LY>  MAXSTEP
LY>   2000
LY>  TRAJECTORY XYZ
LY>  RESTART COORDINATES CELL WAVEFUNCTIONS VELOCITIES ACCUMULATORS NOSEP NOSEE LATEST
LY> &END
LY> 

-- 

=======================================================================
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.