“cmd.intra_rms_cur” calculates rms values for all states of an object over an atom selection relative to the indicated state without performing any fitting. The rms values are returned as a python array.

cmd.intra_rms_cur( string selection, int state)

ON EXAMPLE

from pymol import cmd
rms = cmd.intra_rms_cur("(name ca)",1)

def intra_rms_cur(selection, state=0, quiet=1):

intra_rms_cur | api