Melting points and thermal expansivities of proton-disordered hexagonal ice with several model potentials

Several thermodynamic properties of ice Ih, II, and III are studied by a quasi-harmonic approximation and compared to results of quantum path integral and classical simulations. This approximation allows to obtain thermodynamic information at a fraction of the computational cost of standard simulation methods, and at the same time permits studying quantum effects related to zero point vibrations of the atoms. Specifically we have studied the crystal volume, bulk modulus, kinetic energy, enthalpy and heat capacity of the three ice phases as a function of temperature and pressure. The flexible q-TIP4P/F model of water was employed for this study, although the results concerning the capability of the quasi-harmonic approximation are expected to be valid independently of the employed water model. The quasi-harmonic approximation reproduces with reasonable accuracy the results of quantum and classical simulations showing an improved agreement at low temperatures (T < 100 K). This agreement does not deteriorate as a function of pressure as long as it is not too close to the limit of mechanical stability of the ice phases.

Section: Discussionmentioning

confidence: 99%

“…However this effect is absent in the TIP5P potential and only slightly visible with the ST2 model. 65 …”

Section: A Thermal Expansionmentioning

confidence: 99%

Quasi-harmonic approximation of thermodynamic properties of ice Ih, II, and III

Ramı́rez

Neuerburg²,

Fernández-Serra³

et al. 2012

“…3,9 Using this technique, the free energy of several atomic and molecular solids has been computed. 4,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36 Quite recently a new method to compute the free energies of solids which was denoted as "the Einstein molecule" approach has been proposed. 37,38 This method consists of a slight modification of the Einstein crystal method.…”

Section: Introductionmentioning

confidence: 99%

Computing the free energy of molecular solids by the Einstein molecule approach: Ices XIII and XIV, hard-dumbbells and a patchy model of proteins

Noya

Conde²,

Vega³

2008

The recently proposed Einstein molecule approach is extended to compute the free energy of molecular solids. This method is a variant of the Einstein crystal method of Frenkel and Ladd[J.Chem. Phys. 81, 3188 (1984)]. In order to show its applicability, we have computed the free energy of a hard-dumbbells solid, of two recently discovered solid phases of water, namely, ice XIII and ice XIV, where the interactions between water molecules are described by the rigid non-polarizable TIP4P/2005 model potential, and of several solid phases that are thermodynamically stable for an anisotropic patchy model with octahedral symmetry which mimics proteins. Our calculations show that both the Einstein crystal method and the Einstein molecule approach yield the same results within statistical uncertainty. In addition, we have studied in detail some subtle issues concerning the calculation of the free energy of molecular solids. First, for solids with non-cubic symmetry, we have studied the effect of the shape of the simulation box on the free energy. Our results show that the equilibrium shape of the simulation box must be used to compute the free energy in order to avoid the appearance of artificial stress in the system that will result in an increase of the free energy. In complex solids, such as the solid phases of water, another difficulty is related to the choice of the reference structure. As in some cases there is not an obvious orientation of the molecules, it is not clear how to generate the reference structure. Our results will show that, as long as the structure is not too far from the equilibrium structure, the calculated free energy is invariant to the reference structure used in the free energy calculations. Finally, the strong size dependence of the free energy of solids is also studied.

“…In a previous paper 1 we report the calculated melting temperature of the proton-disordered hexagonal ice I h using a four-site water model, the TIP4P ͑Ref. 2͒ and a five-site model, the TIP5P.…”

mentioning

confidence: 99%

“…For the TIP4P system, two initial temperatures T = 225 and 235 K were chosen, guided by previous simulations with freeenergy method. 1 For the TIP5P system, two initial temperatures T = 265 and 275 K were chosen, again guided by previous simulations. Figures 1͑a͒ and 1͑b͒ instantaneous kinetic temperature T versus the MD time t for the TIP4P and TIP5P systems, respectively.…”

mentioning

confidence: 99%

Melting temperature of ice Ih calculated from coexisting solid-liquid phases

Wang

Yoo

Bai

et al. 2005

Self Cite

We carried out molecular-dynamics simulations by using the two-phase coexistence method with the constant pressure, particle number, and enthalpy ensemble to compute the melting temperature of proton-disordered hexagonal ice Ih at 1-bar pressure. Four models of water were considered, including the widely used TIP4P [W. L. Jorgensen, J. Chandrasekha, J. D. Madura, R. W. Impey, and M. L. Klein, J. Chem. Phys.79, 926 (1983)] and TIP5P [M. W. Mahoney and W. L. Jorgensen J. Chem. Phys.112, 8910 (2000)] models, as well as recently improved TIP4P and TIP5P models for use with Ewald techniques—the TIP4P-Ew [W. Horn, W. C. Swope, J. W. Pitera, J. C. Madura, T. J. Dick, G. L. Hura, and T. Head-Gordon, J. Chem. Phys.120, 9665 (2004)] and TIP5P-Ew [S. W. Rick, J. Chem. Phys.120, 6085 (2004)] models. The calculated melting temperature at 1bar is Tm=229±1K for the TIP4P and Tm=272.0±0.6K for the TIP5P ice Ih, both are consistent with previous simulations based on free-energy methods. For the TIP4P-Ew and TIP5P-Ew models, the calculated melting temperature is Tm=257.0±1.1K and Tm=253.9±1.1K, respectively.