[Wien] Formation energy + some other querries!

[Stefaan Cottenier]

Of course you're right, Gerhard, and I should have been more explicit.  
It depends what you want to do: a strict 0K analysis, or adding some  
(clearly not all) temperature effects. If one of the constituents is  
gaseous at the temperature of interest, it makes sense to calculate a  
formation energy involving that gas phase. It might be more relevant  
from a predictive point of view than the 0K prediction.

> May be its hard to breathe at 0K because oxygen will be solid, too.

One could try to swallow oxygen/nitrogen (20/80) ice cubes as a substitute ;-)

Stefaan



Quoting Gerhard Fecher <fecher at uni-mainz.de>:

> Just to contribute also to the confusion:
> In my lab, the nitrogen is liquid and comes in big barrels. If the   
> gaseous phase of N2 at room temperature is the ground state, does it  
>  mean that the nitrogen in my barrel is deexcited into a sub-ground   
> state
>
> In the textbook on an introduction to solid state physics by Ch.   
> Kittel I found that nitrogen has a cubic structure with a lattice   
> parameter of 0.566 nm at 20K.
>
> May be its hard to breathe at 0K because oxygen will be solid, too.
>
> have fun
> Gerhard
>
> ________________________________________
> Von: wien-bounces at zeus.theochem.tuwien.ac.at   
> [wien-bounces at zeus.theochem.tuwien.ac.at] im Auftrag von Stefaan   
> Cottenier [Stefaan.Cottenier at fys.kuleuven.be]
> Gesendet: Donnerstag, 7. Februar 2008 08:46
> An: wien at zeus.theochem.tuwien.ac.at
> Betreff: Re: [Wien] Formation energy + some other querries!
>
>> Also, just to confirm what Stefaan has said, if one does an atomic
>> calculation for H, the total energy evaluated should be around 1Ryd?
>
> In principle yes. But in practice it can be considerably off, due to
> using LDA/GGA instead of the exact XC functional. It would be a nice
> exercise to do this.
>
> About N: its standard state is the N2 molecule, and this you can treat
> in a big empty cell just as for a free atom. However -- and that is
> what Chandrika referred to -- this will not involve vibrational energy
> of the molecule. Probably you can find such information elsewhere,
> such that you still have a meaningful value for N2.
>
> Stefaan
>
> Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm
>
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>
>



-- 
Stefaan Cottenier
Computational Materials Engineering (CME) &
Center for Computational Engineering Science (CCES)
RWTH Aachen University
Mauerstrasse 5
DE-52064 Aachen
Germany

e-mail: stefaan.cottenier at fys.kuleuven.be (preferred)
         cottenier at ghi.rwth-aachen.de (avoid)


Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm