CHARMM Development Project Forums User Discussion & Questions Molecular Dynamics charmm parameters for a CPT dynamics run (PMASS/PGAMMA)

Dear charmm users,

I am trying to run a CPT dynamics in a given molecular crystal. However, I am not sure if I should the same value of "pgamma" value during the entire molecular dynamics run (i.e., heating, equilibration, and production).

Currently, I am using the following for the HEATING step:
pcons pint pref 1.0 pmass 2000 pgamma 25.0 -

And the following for the EQUILIBRATION step:
pcons pint pref 1.0 pmass 2000 pgamma 5.0 -

Any directions on how to define the pmass and/or pgamma values will be appreciated.

Thanks,

There is some debate about the best practice for that. Setting PGAMMA to zero does give true NPT or NVT dynamics. OTOH, a non-zero PGAMMA is equivalent to a chain of thermostats for T control. Finally, some claim that all thermostats and barostats are flawed, and only NVE dynamics should be used.