[CPMD-list] question on thermal energy tranfer

[Axel Kohlmeyer]

On Sat, 7 Apr 2007, Tengfei Luo wrote:

TL> Dear All:

TL> I have some question on the result of thermal energy equilibration.
TL> Experts, could you please look at my inputs to see if there is
TL> anything wrong?

[...]

TL> But I got a result very strange: the temperature of the two
TL> materials doesn't go a uniform temperature after the thermostates
TL> are erased no matter how many steps I run. I cannot explain this
TL> phenomena physically. Why the temperatures don't go to a same
TL> temperature, but there is indeed a little temperature drop of high
TL> temperature side and a little raise in the low temperature side.

have you considered that - due to different atomic masses - bulk 
Si and bulk Ge have different characteristic frequencies and that
there can be very little overlap of the phonon spectra? even more
so since are running at very low temperature 50/100K so that only
low lying phononic states would be excited.

TL> BTW, When I used silicon in both group and germanium in both group,
TL> the temperature get to a uniform temperature after some thoudands of
TL> steps. (I wrote a little code to process the trajectory file to
TL> evaluate the temperature of each part.)

i suggest, you run the velocities from your trajectories (for each
atom individually and then averaged over groups) through the fourier.x 
code to look at the vibrational spectral densities. bob williams
has contributed some code to the package for that purpose.

cheers,
   axel.

TL> I would like to provide any further information if it's needed!
TL> 
TL> Thank you in advance!
TL> 
TL> Tengfei

-- 
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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
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