[CPMD-list] Nose thermostat

[Axel Kohlmeyer]

On Tue, 4 Sep 2007, Walter Langel wrote:

WL> Hi,
WL> 

as usual, please provide CPMD version, platform,
input and output example.

WL> I have a question concerning the energies in the cpmd output files for 
WL> molecular dynamics with Nose thermostat:
WL> 
WL> Without Nose thermostat, ECLASSIC is simply given as sum of potential 
WL> and kinetic ion energies, EKS+EKION, and the printed out temperature 
WL> TEMPP is related to EKION by
WL> EKION=N kb TEMPP/2 , where N is the number of unconstrainend degrees of 
WL> freedom. (As written in the manual).
WL> 
WL> With Nose thermostat, ECLASSIC-EKS fluctuates very strongly and can take 
WL> negative values (???), even if the printed out value for TEMPP is fairly 
WL> constant around 300 K.
WL> Especially, ECLASSIC-EKS is most of the time completely different from 
WL> the value of EKION, calculated from the value for TEMPP given by the 
WL> program.
WL> 
WL> Can anyone tell me, what the meaning of ECLASSIC is when unsing the Nose 
WL> thermostat, and how it is calculated then.

in general, ECLASSIC should be the conserved quantity (EHAM) minus 
the kinetic energy of the fictitious electron dynamics (EKINC).
in the case of nose-hoover thermostat chains, the conserved 
quantity of the NH-chains should be included.
there may be a few inconsistencies between job types (i suggest to
rather read the sources than trust the manual) due to the existence
of quite a few 'MD-drivers' that were branched off at different times
and not always fully maintained or merged back in without adding
updates that were added to other drivers.

cheers,
   axel.


WL> 
WL> Thanks
WL> 
WL> Walter Langel
WL> 
WL> 

-- 
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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
   Center for Molecular Modeling   --   University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
tel: 1-215-898-1582,  fax: 1-215-573-6233,  office-tel: 1-215-898-5425
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