tclforces: switch from md with external forces to standard md

From: Vlad Cojocaru (
Date: Tue Dec 23 2008 - 09:01:36 CST

Dear namd users,

I have another question regarding tclforces.

I would like that my tcl script switches at specific intervals between
simulation with external forces and standard md simulation.
So, I introduced a flag and invoked the "addforce" command only if the
flag is defined. After each stint with external forces, I unset the flag
and reset it after the standard md steps.

However, I noticed that once the switch occurs, the external force does
not disappear. In fact the value given by loadforces command stays
constant during the standard md part and equals the last value from the
part with external forces. From the trajectory, I guess that the
external force is still being applied on my system even during the
desired standard md simulation part.

Am I right here? Does "addforce" actually adds up forces added at each
time step ?
If yes, is it possible to alter this behavior and reset the external
force to 0 after specific intervals ?

Thanks for answering

Merry Christmas and Happy New Year to all of you.


Dr. Vlad Cojocaru
EML Research gGmbH
Schloss-Wolfsbrunnenweg 33
69118 Heidelberg
Tel: ++49-6221-533202
Fax: ++49-6221-533298
EML Research gGmbH
Amtgericht Mannheim / HRB 337446
Managing Partner: Dr. h.c. Klaus Tschira
Scientific and Managing Director: Prof. Dr.-Ing. Andreas Reuter

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