**************** The 15th., Lab Seminar *****************

Date: Thu, November 25, 2004  PM 1:30-

Place: No.616 Seminar room
　　　　　　 Graduate School of Information Science

Speaker: Yoshiyuki Koyano
　　　　　
Title: Melting points and thermal expansivities of proton-disordered hexagonal ice 
with several model potentials
Y. Koyama, H. Tanaka, G. Gao and X. C. Zeng, 
J. Chem. Phys., 121(2004), 7926.

Abstract:
 A method of free energy calculation is proposed, which enables to cover a wide 
range of pressure and temperature. The free energies of proton-disordered 
hexagonal ice (ice Ih) and liquid water are calculated for the TIP4P [J. Chem. 
Phys. 79, 926 (1983)] model and the TIP5P [J. Chem. Phys. 112, 8910 (2000)] 
model. From the calculated free energy curves, we determine the melting point 
of the proton-disordered hexagonal ice at 0.1 MPa (atmospheric pressure), 
50 MPa, 100 MPa, and 200 MPa. The melting temperatures at atmospheric 
pressure for the TIP4P ice and the TIP5P ice are found to be about Tm = 229 K 
and Tm = 268 K, respectively. The melting temperatures decrease as the pressure 
is increased, a feature consistent with the pressure dependence of the melting 
point for realistic proton-disordered hexagonal ice. We also calculate the thermal 
expansivity of the model ices. Negative thermal expansivity is observed at the 
low temperature region for the TIP4P ice, but not for the TIP5P ice at the 
ambient pressure. 

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