unanswered Water freezing with different solvation methods

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10 months 1 week ago #8800 by almeida
Hi all,

I am working with multiscale systems, where a region of the system is atomistic and the rest is coarse-grained. The simulation box size is 10x10x10 nm. The atomistic region is defined as a sphere of increasing radius around the system's COM (similar to pubs.acs.org/doi/10.1021/acs.jctc.5b00499 ). To build the systems, first I obtain the TIP3P atomistic region of different radius (r(AA)) and then, solvated with stdW MARTINI's waters, using gmx solvate or inane.py. After minimization, I want to do some 500 ps NVT equilibration. To avoid systems to mix I applied spherical flat-bottom restrains to both AA and CG waters.

For those systems solvated with gmx solvate with r(AA) >= 25 A, the stdW freeze, while those r(AA) < 25 A worked OK. The inverse behavior happens if I use insane.py. Those with r(AA) <= 25 A freeze, while r(AA) > 25 A is fine.

In the beginning, I thought this was due to the restraining force of K=1000 kJ mol^-1 nm^-2 used. I decreased to K=300 kJ mol^-1 nm^-2 with the same behavior. insane.py solvate with more stdW than gmx solvate.

Does anyone has seen this weird behavior before? I am aware of the water freezing but this dependency with the solvation method is quite strange. I want to understand what is happening before using anti-freezing waters.

Thanks in advance,
-Yasser

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