Equipartition and the temperature of maximum density of TIP4/2005 water
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| Format: | Preprint |
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2025
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| _version_ | 1866909855815565312 |
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| author | Asthagiri, Dilipkumar N. Santos, Thiago Pinheiro dos Beck, Thomas L. |
| author_facet | Asthagiri, Dilipkumar N. Santos, Thiago Pinheiro dos Beck, Thomas L. |
| contents | We simulate TIP4P/2005 water in the temperature range of 257 K to 318 K with time-steps $δ=$ 0.25, 0.50, 2.00, and 4.00 fs. The density-temperature behavior obtained using 0.25 or 0.50 fs are in excellent agreement with each other but differ from those obtained using time-steps that have been shown earlier to lead to a breakdown of equipartition. The temperature of maximum density (TMD) is 277.15 K with $δt = 0.25\;\mathrm{or}\; 0.50$ fs, but is shifted to progressively lower values for longer time-steps, a trend that holds for different thermostat/barostat combinations. Enhancing the water-water dispersion interaction, as has been recommended for simulating disordered proteins in TIP4P/2005, degrades the description of the liquid-vapor phase envelope. A key takeaway from this study is that using sufficiently short time-steps ($\leq 0.5$ fs) to preserve equipartition is essential for obtaining meaningful liquid water properties and for producing reliable data to parametrize biomolecular simulation models, as correct-ensemble sampling is fundamental to ensure reproducibility across codes and simulation alogrithms. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2508_14800 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Equipartition and the temperature of maximum density of TIP4/2005 water Asthagiri, Dilipkumar N. Santos, Thiago Pinheiro dos Beck, Thomas L. Soft Condensed Matter Chemical Physics We simulate TIP4P/2005 water in the temperature range of 257 K to 318 K with time-steps $δ=$ 0.25, 0.50, 2.00, and 4.00 fs. The density-temperature behavior obtained using 0.25 or 0.50 fs are in excellent agreement with each other but differ from those obtained using time-steps that have been shown earlier to lead to a breakdown of equipartition. The temperature of maximum density (TMD) is 277.15 K with $δt = 0.25\;\mathrm{or}\; 0.50$ fs, but is shifted to progressively lower values for longer time-steps, a trend that holds for different thermostat/barostat combinations. Enhancing the water-water dispersion interaction, as has been recommended for simulating disordered proteins in TIP4P/2005, degrades the description of the liquid-vapor phase envelope. A key takeaway from this study is that using sufficiently short time-steps ($\leq 0.5$ fs) to preserve equipartition is essential for obtaining meaningful liquid water properties and for producing reliable data to parametrize biomolecular simulation models, as correct-ensemble sampling is fundamental to ensure reproducibility across codes and simulation alogrithms. |
| title | Equipartition and the temperature of maximum density of TIP4/2005 water |
| topic | Soft Condensed Matter Chemical Physics |
| url | https://arxiv.org/abs/2508.14800 |