[Wien] Ionic versus covalent systems

[jadhikari@clarku.edu]

Dear Wien2k users,

I did calculations of compounds containing "Calcium ions" and it was
extremely tough to get the converged results. The calculations of similar
compounds, replacing Calcium with "Lead ions" was extremely easy and of
course superbly fast. All that was done was "Ca" replacex with "Pb".

So the questions ( basic) are-
Is it the former being more ionic we are having problems and that the
latter being more covalent all of the troubles are gone?

Is is because of localized versus delocalized systems?

Following compounds- LiZnN, LiMgN, LiMn2O4, NaNbO3, MgAl2O4, CaCu3Ti4O12
possess ionic characteristics and NaNbO3 is an example of a tougher system
for convergence. 9 IBZ with RKmax of 6 or greater is extremly time
consuming. The published article is silent about the RKmax and the test
for higher IBZ points.

Is it because of "Na" ion in the system or it does not matter?

Looking forward for just a general idea.

Thanking you

Subin Adhikari