[Wien] How close to overlapping RMT's is too close?

[Stefaan Cottenier]

> I have indications from a minimization that the energy/forces can be
> slightly inconsistent if two atoms are too close but still far
> enough
> apart that the RMT's are not overlapping. Has anyone else noticed
> this?

Some years ago, I calculated the total energy of a simple compound 
(without forces) as a function of volume, and this with two different 
Rmt's. With the smallest Rmt, smaller volumes could be done. In the 
volume range where there were data for both Rmt's, total energies were 
identical (apart from a small shift), except for the small region 
where the Rmt's of the series with largest Rmt were just not yet 
overlapping: there the total energy clearly deviated. Hence, I can 
confirm your observation: very close to overlap, some quantities 
become unreliable (which is not too surprizing). How close to overlap 
the problem occurred in my case, I do not remember. But definitely the 
two sphere surfaces were closer than 0.1 au, probably 0.05 au or so.

Stefaan