[CPMD-list] Energy components in PIMD

[Axel Kohlmeyer]

On Tue, 27 May 2008, ukasz Walewski wrote:

LW> > yep. so either you have to live with what you have using the 
LW> > translation/rotation correction infrequently, remove the subtract
LW> > COMVEL/ROTVEL altogether after equilibration or use 3 or 4 _very_
LW> > soft position _restraints_ on some of the outer carbon atoms that
LW> > will also make sure that the system stays where it should.
LW> 
LW> Well, I will try the last option. However I have no clue on what "very
LW> soft" means, i.e. what might be the "soft" value for kval ? The manual
LW> is silent on the units of this parameter. Otherwise one could have taken
LW> the force constant of the C-H bond from any common force filed (e.g.
LW> Gromos) and divide it by 10 or even 100. What is your recommendation ?

i don't know what a proper value is, i would play around with a simple
system (benzene?) and low cutoff (you don't care about the correct 
structure). if you do a single point wavefunction optimization with 
PRINT FORCES ON, you see the typical size of forces. just do a guess
of what kind of force you want to see at what distance from a position.
even a very small force constant should work, since the the system
should stay in position anyways.

cheers,
   axel.

LW> 
LW> Best regards,
LW> Lukasz
LW> 

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