rotating constraints

From: himanshu chandola (beu99419_at_ccsun50.iitd.ernet.in)
Date: Fri Jan 30 2004 - 01:28:51 CST

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hi all -
        referring to the rotating constraints feature in namd. We know
that the force is 2K(R-X). Now R is the current reference position
which should hence lie in the rotational circle in which we rotated the
atom - and as we've already given the angular velocity of rotation we
already know the current reference position at any time.

My problem is about X. Now though the manual doesn't say it - X should be
the current position of the atom(i'm sorry if i'm wrong and ofcourse all
these quantities are vectors).

My problem is in calculating the torque which i've put on each atom.
Though it appears easy to do - how can the torque be zero if i have put my
spring constants so stiff that the atoms being rotated follow their
reference point very closely.

Now - i am sure that i am wrong somewhere - could you please point out
where i am wrong - and hence how the torque applied on the atom
calculated.

thanks

himanshu
iit delhi

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