Making mass fraction compatible with calculations
So, in computation one can also have non-standard elements, currently represented as X
in ase.chemical_symbols
.
Atm, any formula that contains X
gets mass_fraction = NaN
which raises an error when serializing into JSON.
So, this has to be ammended when mapping / normalizing run
into results
.
More specifically, X
should show up in results.material.elemental_composition
.
Regarding the mass fraction, things are bit more blurry, since X
has no clear semantics (or mass for that matter).
Calculations may employ alternative elements for a variety of reasons.
I'll see to compile a list, ghost atoms would be one example.
So, I see 2 options:
- we assign a ficitional mass to
X
. This would most likely be 0 a.u., which works fine for cases where they do not represent any known element. - we do not provide any mass fraction, but instead generate a specific warning explaining why, rather than an obscure error.