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| Main Authors: | , , |
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| Format: | Preprint |
| Published: |
2024
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2412.03448 |
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Table of Contents:
- Earlier we showed that in the molecular dynamics simulation of a rigid model of water it is necessary to use an integration time-step $δt \leq 0.5$ fs to ensure equipartition between translational and rotational modes. Here we extend that study in the $NVT$ ensemble to $NpT$ conditions and to an aqueous protein. We study neat liquid water with the rigid, SPC/E model and the protein BBA (PDB ID: 1FME) solvated in the rigid, TIP3P model. We examine integration time-steps ranging from $0.5$ fs to $4.0$ fs for various thermostat plus barostat combinations. We find that a small $δt$ is necessary to ensure consistent prediction of the simulation volume. Hydrogen mass repartitioning alleviates the problem somewhat, but is ineffective for the typical time-step used with this approach. The compressibility, a measure of volume fluctuations, and the dielectric constant, a measure of dipole moment fluctuations, are also seen to be sensitive to $δt$. Using the mean volume estimated from the $NpT$ simulation, we examine the electrostatic and van der Waals contribution to the hydration free energy of the protein in the $NVT$ ensemble. These contributions are also sensitive to $δt$. In going from $δt = 2$ fs to $δt = 0.5$ fs, the change in the net electrostatic plus van der Waals contribution to the hydration of BBA is already in excess of the folding free energy reported for this protein.