out-of-plane torsion

Dear Lammps users,

There is any news about out-of-plane torsion impropers (r^2 r^4 form)?
Steve Plimpton, said something, last year, about Paolo including these kind of interactions on the code (http://lammps.sandia.gov/threads/msg29909.html).

I would like to use these kind of interactions to describe the impropers of calcite CO3 group.

Best regards,

James Moraes de Almeida