[Pw_forum] temperature oscillations with nose' thermostat

[Axel Kohlmeyer]

On Mon, 6 Jun 2005, Massimiliano Bonomi wrote:

MB>   Dear users,

[...]

massimiliano,

MB> During a simulation of 10000 time step (~ 1.0 picoseconds) at T=300K  
MB> the temperature of the system  made big oscillations around 300K (even 
MB> of 200K!!).
MB> 
MB> Is it normal?? How can i reduce the width of these oscillations?

probably yes. it depends a bit on the number of movable atoms.
the fewer atoms you have, the larger the oscillations.
just think of it as bunch of two atom oscillators. for each of them,
the kinetic energy becomes zero at the turning points. they won't all
have the exeact same frequency and phase, so if you have a large number
of them, this averages out. to give you an estimate, for a system with
33 water molecules at 300K the instantaneous temperature may easily go
up to 400K or down to 200K.

best regards,
	axel.

MB> 
MB> Best regards and thanks in advance.
MB> Massimiliano Bonomi.
MB> 
MB> 

-- 

=======================================================================
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/
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If you make something idiot-proof, the universe creates a better idiot.