access unwrapped coordinates

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1

Dear users,

I am trying to access unwrapped coordinates xu[atom-id]

While I can define without probles variables such as

variable h equal x[${b}] ,

as I try to substitute “x” with “xu”, i.e.

variable h equal xu[${b}]

i get this error

ERROR on proc 0: Invalid atom vector in variable formula (…/variable.cpp:3587)

does the access to xu-coordinates need something more to be accessed?

Best regards and many thanks for any hint.

Mario

2

Dear users,

I am trying to access unwrapped coordinates xu[atom-id]

While I can define without probles variables such as

variable h equal x[${b}] ,

as I try to substitute "x" with "xu", i.e.

variable h equal xu[${b}]

i get this error

ERROR on proc 0: Invalid atom vector in variable formula
(../variable.cpp:3587)

does the access to xu-coordinates need something more to be accessed?

there (currently) is no such xu property for variable expressions.

3

Thank you, Axel.

Kind regards

Mario

4

But every atom property that LAMMPS stores can be

accessed via compute property/atom, and a compute can
be accessed in a variable. That’s why we don’t make
a long list of per-atom properties directly reference-able
in per-atom variables.

Steve

5

Dear Steve,

Thanks for the answer.

So, do you mean something like

Compute 4 property/atom xu
variable a equal c_4[700] (print xu coordinate of atom #700)
print “$a”

Should it work? I apologize if the form I written is not correct, but I’m writing from my phone now. I tried this way too but it didn’t work. Excuse me if the question is too elementary.

Thanks for advice

Best regards

Mario

6

Your compute command is not correct syntax. You also
cannot execute this before a run, like for variable with many other computes.

See the variable doc page for details.

Steve