[Pw_forum] Rydberg to KJ/mole - polymorphs

[Lorenzo Paulatto]

> My energy differences of 120 and 240 kJ/mole are far too high for
> polymorphs (see ref [1]).
> Am I mistaken to equalize the "total energy" of pwscf-output with the
> "lattice energy" (former "structure energy")?
> I'm aware of the missing Entropy - but it is told to be negligible  
> small...

I'm not entirely sure I understand your problem; I just want to remind  
that total energy periodic system does not have any absolute meaning: only  
energy differences count. So, with what are you comparing the energy of  
your crystal?

As your reference is in kJ/mol your reference could be the homo-atomic  
molecular phase of the constituents, i.e. O2, N2, H2, and in whetever form  
C and P are normally bought by a chemistry lab. Another possibility is to  
compare with isolated atoms, this gives you the binding energy of the  
crystal. I suspect the details are somewhere in [1].

> I do use nc pseudopotentials and my system is composed of
> triphenylphosphine moities with aminobenzoic acids connected.

In any case, you MUST use the same pseudopotential and cutoffs when doing  
the reference calculation for the comparison to be useful.

bests





-- 
Lorenzo Paulatto IdR @ IMPMC/UPMC CNRS & Université Paris 6
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