[Pw_forum] Definition of PsP in LDA+U + rotational freuqncies of molecules

[Nicola Marzari]

Dear Sergey,

The masses of the atoms are only relevant in the case of a
phonon or a molecular dynamics calculation.

For the case of phonons, note that the interatomic force constants are
independent of the masses, but the phonon frequencies are not (although
they depend trivially on them via an inverse square root)

Note also that in a molecular dynamics simulation with classical
nuclei and boltzmann statistics (as it happens for pwscf, fpmd, and
cp) the dynamical properties (e.g. diffusion coefficient) will depend
on the masses, but the thermodynamical ones (e.g. the temperature
of a phase transition) will not (the kinetic energy integral factors
out in the expectation value of observables that do not depend on
momenta). Quantum effects change this, usually mildly (e.g. the
freezing temperatre of heavy water differs by only 4K from that
of regular water).

On a different matter, a post yesterday was mentioning vibrational
frequencies for H_2 . A new, hopefully improved set of acoustic
sum rules has been recently implemented in Pwscf by Nicolas Mounet,
from our group. This should take care of all the zero-frequency
modes for isolated systems.

Best,

			nicola

Sergey Lisenkov wrote:

> Dear Pwscf users and authors,
> 
>  I look at input file of example 25 of espresso distribution and see:
> 
> .....
> ATOMIC_SPECIES
>  O1   1.  O.LDA.US.RRKJ3.UPF
>  Fe1  1.  Fe.pz-nd-rrkjus.UPF
>  Fe2  1.  Fe.pz-nd-rrkjus.UPF
> ........
> 
> Why all masses of PsP are equal to 1? Does it affect to calculations?
> 
>  Thanks, 
>    Sergey
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Prof Nicola Marzari   Department of Materials Science and Engineering
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