Anomalies in water as obtained from computer simulations of the TIP4P/2005 model: density maxima, and density, isothermal compressibility and heat capacity minima

Abstract

The so-called thermodynamic anomalies of water form an integral part of the peculiar behaviour of this both important and ubiquitous molecule. In this paper our aim is to establish whether the recently proposed TIP4P/2005 model is capable of reproducing a number of these anomalies. Using molecular dynamics simulations we investigate both the maximum in density and the minimum in the isothermal compressibility along a number of isobars. It is shown that the model correctly describes the decrease in the temperature of the density maximum with increasing pressure. At atmospheric pressure the model exhibits an additional minimum in density at a temperature of about 200K, in good agreement with recent experimental work on super-cooled confined water. The model also presents a minimum in the isothermal compressibility close to 310K. We have also investigated the atmospheric pressure isobar for three other water models; the SPC/E and TIP4P models also present a minimum in the isothermal compressibility, although at a considerably lower temperature than the experimental one. For the temperature range considered no such minimum is found for the TIP5P model.

Keywords:

• water anomalies
• computer simulation
• TIP4P/2005
• maximum in density
• isothermal compressibility

Acknowledgements

This work has been funded by grants FIS2007-66079-C02-01 from the DGI (Spain), S-0505/ESP/0299 from the CAM, and 910570 from the UCM. EGN would like to thank MICINN for a Juan de la Cierva fellowship. JLA would like to thank MICINN for the award of a FPI PhD grant.