Hi all,
I want to constrain the center-of-mass of a liquid droplet when the liquid droplet is evaporating.
Thus, I must use a dynamic group to update the atoms in the liquid drop.
But the fix recenter command does not allow use of dynamic group.
So what shall I do to over come this problem?
Best regards and many thanks!
Tianbao Wang
Hi all,
I want to constrain the center-of-mass of a liquid droplet when the liquid
droplet is evaporating.Thus, I must use a dynamic group to update the atoms in the liquid drop.
But the fix recenter command does not allow use of dynamic group.
So what shall I do to over come this problem?
three comments:
1) fix recenter does *not* do constraining. it merely translates the whole
system so that the center of mass of the fix group remains stationary. if
you want proper constraining to happen, you have to use fix spring in
tether mode.
2) support for dynamic groups in fixes can be enabled through altering the
source code. to bypass the test causing the error, you only need to set a
flag. however, that does not guarantee that the fix works correctly with
dynamic groups. this instead requires a careful auditing and testing of the
code and, if needed, suitable additional changes to the source. this can be
time consuming and thus support for dynamic groups is by default disabled.
3) the recentering as it would happen with fix recenter can easily be done
in post-processing, since it does not alter the dynamics in anyway. for
example the pbctools plugin in VMD contains features to perform such an
operation.
axel.
I also tried fix spring but it does not support dynamic group either.
For some reason I must control the center-of-mass of the droplet at a certain position in my simulation.
So I will try your the second comment and see what will happen.
Thanks very much!
Tianbao
I also tried fix spring but it does not support dynamic group either.
...and for the same reason.
For some reason I must control the center-of-mass of the droplet at a
certain position in my simulation.
let me reiterate, fix recenter does no such thing. it merely changes the
frame of reference.
whatever that mysterious reason of yours is, you have to be careful with
how you manipulate your system either way.
axel.
Ok, now I see.
Fix spring is more suitable for my case.
Thanks very much!
Tianbao