[Wien] O2 molecule continue (rmt issue)

[SM Alay-e-Abbas]

Good to see more details added to the FAQ on cohesive/formation energies. I
have two suggestions for the new FAQ on cohesive energies

1- Computing the atomic energies of atoms like N and P in an FCC cell is
ok, however for O atom the high symmetry of the FCC cell results in 1/3
occupancies (for the 4th p electron of O) in the spin down case. Only using
a lower symmetry cell (orthorhombic) for O atom eliminates this issue.

2- For very small RMTs (e.g. 1.1 for O) one needs a large value of Gmax
(~20).

and one question

Using RMT = 1.1 for O in a compound will require one to use too small RMTs
for large atoms. For example if we use RMT = 1.1 for O in compounds like
SnO2, this will require one to use an RMT ~ 1.6 for Sn (RMTs difference
should not be > 30 %). This means that the ecut should be set < -9.8 Ry
which includes the 4s electrons to valence states. What are the
consequences?

Best Regards,

Alay
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