NpT simulations for TIP4P/2005: Virtual Site Constraint/Restraint not implemented for SHAKE_ROLL!
christia... at gmail.com
Wed Aug 2 19:12:47 UTC 2017
I am trying to run a NpT simulation using the TIP4P/2005 water model, which
has an auxiliary charge site near the oxygen. To do that, I have modified
the water_tip4p.inp input file from the tests/Fist/regtest-5 directory. NVE
works fine, as do NVT runs, however, there is a problem when trying to run
"Virtual Site Constraint/Restraint not implemented for SHAKE_ROLL!"
As a matter of fact, this has been noted before:
Any idea if there es a way around that? How difficult would it be to
actually implement the virtual site constraint for the SHAKE_ROLL
algorithm? I know Fortran and I have implemented integrators before, but I
assume there is a good reason why it is not implemented in the current code
One other idea, could I instead define the "virtual" site as a regular
particle with the proper constraints and parameters (such as zero mass)? In
other words, what is the exact purpose of a virtual site vs. a regular one?
I have noted that despite the TIP4P auxiliary site being defined as a
virtual site in the input file, I still have to provide it explicitly in my
XYZ co-ordinate input file as well. Same is true for the output XYZ, there
the virtual site is included as well.
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