[lammps-users] about fix rigid and compute pressure


I am confused by how to use compute pressure command in fixing rigid system. I use fix rigid command to build a DNA helix structure of 50 atoms, which isn’t a linear rigid body. There are 100 DNA macromolecules. BUT then, I don’t know how to compute system pressure. I read the manual carefully, but I can’t completely understand how many extra degrees - of -freedom should be subtracted with compute_modify command.

50 atoms have 503 degrees of freedom and one rigid have 6 degrees then whether there are 100(50*3 - 6) degrees of freedom which shoud be subtracted. Is it right?

Thanks in advance.