[Pw_forum] cp with metals

[Konstantin Kudin]

 Hi all,

 I'd like to point out that electronic thermostats is a pretty
dangeorous thing to use for any production calculations unless one
really knows what is going on there.

 The main issue is that there is usually some "natural" fictitious
kinetic energy that electrons gain from the ionic motion ("drag"). One
could easily quantify how much of the fictitious energy comes from this
drag by doing a CP run, then a couple of CG (same as BO) steps, and
then going back to CP. The fictitious electronic energy at the last CP
restart will be purely due to the drag effect.

 The thermostat on electrons will either try to overexcite the
otherwise "cold" electrons, or, will try to take them down to an
unnaturally cold state where their fictitious kinetic energy is even
below what would be just due pure drag. Neither of this is good.

 I think the only workable regime with an electronic thermostat is a
mild overexcitation of the electrons, however, to do this one will need
to know rather precisely what is the fictititious kinetic energy due to
the drag.

 Kostya


--- Davide Ceresoli <ceresoli at sissa.it> wrote:

> Nichols A. Romero wrote:
> > Hi,
> > 
> > How does the Car-Parinello MD code in the ESPRESSO package handle
> > metallic cases? Does it implement the method by Blochl et. al PRB
> 45,
> > 9413 (1992).
> > 
> Yes, in namelist &electrons:
>      electron_temperature = 'nose' or 'rescaling'
> 
> Best,
>      Davide



		
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