[CPMD-list] What are classic energies for CP MD and PI MD?

[Axel Kohlmeyer]

On Tue, 6 Dec 2005, Lan-Feng Yuan (lyuan at Princeton.EDU) wrote:

LF>   Dear CPMD community,

dear lan-feng,

LF>   I am using CPMD to do path integral simulations and find it very
LF> useful, thanks! The total quantum energy in output corresponds to
LF> the total energy estimator, and by subtracting the nuclear ground
LF> state energy, I can get the vibrational energy at a given
LF> temperature. Well, what is the "ECLASSIC" in output? Also, in a

i can't speak for the PI-MD case, but ...

LF> classic CP MD simulation, "ECLASSIC" is also printed. Are they the
LF> same thing? I guess it's the sum of Kohn-Sham energy and classic
LF> nuclear kinetic energy (which is proportional to instant
LF> temperature). If this is correct, then ECLASSIC - EKS should be
LF> equal to 3/2*N*k_B*T (N is number of atoms) when average temperature
LF> reaches its target value, right? However, it seems that I never get
LF> it exact. What's the problem? Thank you very much!

are you doing an isolated system (symmetry 0)? 
then you have only 3N-3 DOFs.

axel.

LF> 
LF>   Best regards,
LF> 
LF>   Lan-Feng
LF> 
LF> ----------------------------
LF> Dr. Lan-Feng Yuan,
LF> Postdoctoral Associate,
LF> Department of Chemistry,
LF> Princeton University,
LF> Princeton, NJ 08544, USA
LF> Office Phone: 1-609-258-1834
LF> Fax: 1-609-258-6746
LF> ----------------------------
LF> _______________________________________________
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LF> CPMD-list at cpmd.org
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LF> 

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