MPI environment variables with parallel LAMMPS


I can read on the manual in Section 12.1 Errors-Common problems:

"In parallel, one way LAMMPS can hang is due to how different MPI implementations handle buffering of
messages. If the code hangs without an error message, it may be that you need to specify an MPI setting or two
(usually via an environment variable) to enable buffering or boost the sizes of messages that can be buffered".

Since in my simulation LAMMPS hangs pretty much as described , does anybody have any idea of which variable to set in MVAPICH2?