1. MD Studies of LDL and HDL phases of Supercooled Water
Xiaohai Li (ChBE)
Vamsi Akkineni (PHYS)
Jianwei Wang (GEOL)

2. Project Goals
Use Molecular Dynamics to simulate the LDL and HDL phases of supercooled water
Obtain the radial distribution functions of two liquid phases of water
Compare Results with literature results

3. Motivation
The liquid-liquid phase transition hypothesis is difficult to prove experimentally because of homogeneous necleation
Computer simulation becomes extremely useful in this case because nucleation does not occur on the timescale of computer simulation

4. The proposed phase diagram of supercooled water
(O. Mishima, and H. E. Stanley, Nature 396, 329(1998))

5. Intermolecular Potentials of water
Interactions between water molecules are far more complicated than those between particles of simple liquids
The ability of water molecules to form hydrogen bonds
The existence of substantial non-additive three- and high-body terms
The simulation are highly sensitive to the intermolecular potential functions used

6. Intermolecular potentials of water
Three kinds of intermolecular potentials
SPC TIP4P ST2

7. SPC Potential Charge on H: +0.41e and charge on O: -0.82e
Angle of HOH: °
Length of OH: 1.0Å
 = 3.166Å
= 78.2 K
kOH = 4637 kJ/(mol Å2) kHOH = 383 kJ/(mol rad2)

8. MD Simulation Ensemble: NVT Number of water molecules: 125
Use periodic boundry conditions
Time step: 0.001ps
Equilibration: 500ps
Collect data: 1000ps
Ewald summation used for long range Coulombic forces.
Cutoff used for Lennard-Jones interactions (7Å)

9. Snapshots of Two Systems
T=150k, d=0.95g/cm T=150k, d=1.20g/cm3

11. (Huang et al.)

12. Site-site radial distribution functions from EPSR simulations
(A. K. Soper, and M. A. Ricci, Phys. Rev. Lett. 84,2881(2000))

13. Conclusion SPC model is suitable for simulating the supercooled water
Our simulation supports the conjecture of LDL and HDL phases at low temperature
More state points can be simulated to find the second critical point