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Repozytorium publikacji
Politechniki Gdańskiej

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Entropy of water calculated from harmonic approximation: estimation of the accuracy of method

Some molecular dynamics simulations were performed for liquid TIP4P and SPC water at a constant density (1.00 g/cm(3)) and within the temperature range of 5-90 degrees C. By using harmonic approximation, both the entropy of water S-H and the specific heat c(v) were calculated, and the results were compared to literature data. It was found that harmonic approximation overestimates absolute entropy of TIP4P water by 5.6 J/mol K (similar to 9.5%) at 278 K, but only by 0.4 J/mol K (similar to 0.5%) at 363 K. The value of the specific heat, however, is strongly underestimated: for TIP4P and SPC model, we obtain 59.5 and 56.9 J/mol K using harmonic approximation, while the correct values are 79.0 and 72.3 J/mol K, respectively.

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