[xcrysden] Why is the final coordinates of pwscf output shown in Xcrysden in unit of alat different from the values shown in the pwscf output?

[Tone Kokalj]

On Tue, 2015-11-17 at 14:17 +0100, liyincumt at gmail.com wrote:
> Dear Xcrysden community,
> 
> I encountered a strange problem with Xcrysden. I was visualizing  the
> final structure after geometry optimization using Xcrysden. When the
> coordinates of atoms shown in Xcrysden in the unit of crystal, they
> are same with those in pw.x output. But after I switched the unit
> from crystal to alat, I found those values are a little different
> from what were written in pw.x output file.

There can be two reasons: if they are marginally different the reason
may be due to, say, round-off errors.

But if they differ considerably the reason is different: in xcrysden
the "alat" always refers to the length of the first Bravais lattice
vector, whereas in pw.x the "alat" is the size of celldm(1) (or A).
Hence, if you set the celldm(1) (or A) to a value different then the
size of the first Bravais lattice vector in the input, then xcrysden's
alat and pw.x alat coordinates will be different.

But to be sure, what is the case in your situation, please post the
pertinent output file.


Regards, Tone

-- 
Anton Kokalj
J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia 
(tel: +386-1-477-3523 // fax:+386-1-477-3822)

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