[lammps-users] fix rigid and temperature computing

Hi ,

I am confused by the fix rigid command and compute comperature command. I don’t know how to determine the number of extra degrees-of-freedom , which should be subtracted.

For example, there is a sphere rigid body composed of 100 atoms. How many degrees-of-freedom should be subtracted?

In my opinion, rigid only have 6 degrees-of-freedom in 3D, there are (3 * 100 - 6) degrees-of-freedom subtracted , Is it right?
Are there some books or articles which introduce how to compute degrees-of-freedom?


If you’re just talking about measuring the temperature of the system, you don’t really have to worry about degrees of freedom anymore unless you’re using the 2001 Fortran code or something. By applying the temperature measurement or control to only the non-rigid bodies it will automatically use the right number of degrees of freedom. If you do need the rigid bodies’ temperature you can apply the temperature measurement to only the rigid body and it will subtract the right degrees of freedom, unless it is a linear rigid body where there is a correction, which yours isn’t.

Any basic stat mech text will explain about degrees of freedom.

Hope this helps,

Chris is correct. The fix rigid doc page has some discussion of dof.