add common cations that bind to MOFs

[khavernathy]

Would it be (easily) possible to add the alkali cations to the range of sorbates in the MCMD code (employing their UFF parameters) ?
My request relates to the fact that in almost all zeolites, and also in an increasing number of charged MOFs there is an unknown distribution
of movable cations sitting in the void space of the framework compounds.

It would just be great if MCMD would allow to find their energetically most favorable positions by insertion / translation moves.
I do not know if your code strictly requires charge neutrality ( I know that the check for that can be turned off).
It would presumbly require to set a stringent fixed loading number for adding cations by GCMC in order to avoid Coulombic explosions.

[khavernathy]

added alkali metals up to Rb here: 825c03f