Introduction
We are currently developing a new potential energy function which models the interaction between water molecules over a range of environments going from the water dimer to liquid water to ice. The molecules are treated as rigid objets and the total interaction energy is separated into electrostatic, induction, dispersion and repulsion components. The dominant attractive interaction, i.e. the electrostatic interaction, is represented by means of a multipole expansion around the center of mass. The induction energy is introduced by solving self-polarization equations in which both dipole and quadrupole moments are induced. For this purpose, dipole-dipole, dipole-quadrupole and quadrupole-quadrupole polarizabilities are used. The dispersion energy is calculated by using generalized London terms (-Cn R -n , where n=6, 8 and 10).
We are currently developing a new potential energy function which models the interaction between water molecules over a range of environments going from the water dimer to liquid water to ice. The molecules are treated as rigid objets and the total interaction energy is separated into electrostatic, induction, dispersion and repulsion components. The dominant attractive interaction, i.e. the electrostatic interaction, is represented by means of a multipole expansion around the center of mass. The induction energy is introduced by solving self-polarization equations in which both dipole and quadrupole moments are induced. For this purpose, dipole-dipole, dipole-quadrupole and quadrupole-quadrupole polarizabilities are used. The dispersion energy is calculated by using generalized London terms (-Cn R -n , where n=6, 8 and 10).
Finally,
the repulsion interaction consists of a two-body
term and a many-body term dependent
on the electron density in the area near a given molecule.[1]
Results
To assess the accuracy of the potential we have studied the (H2O)n=2-6 clusters and the proton disordered phase of ice (ice Ih). Our results are in good agreement with the available experimental and theoretical results. For example, the experimentally estimated lattice energy of the crystal is 0.6110 eV/molec[2] while the value obtained with our potential is 0.6109 eV/molec. The structural parameters predicted by the same calculations are also in good agreement with the available experimental values, as shown in the following table:
The results for the (H2O)n clusters are also in good agreement with the available experimental and theoretical values:
References
Results
To assess the accuracy of the potential we have studied the (H2O)n=2-6 clusters and the proton disordered phase of ice (ice Ih). Our results are in good agreement with the available experimental and theoretical results. For example, the experimentally estimated lattice energy of the crystal is 0.6110 eV/molec[2] while the value obtained with our potential is 0.6109 eV/molec. The structural parameters predicted by the same calculations are also in good agreement with the available experimental values, as shown in the following table:
| Quantity |
Calculated |
Experimental [2] |
| < ROO> |
2.7419 Å |
2.751 Å |
| < u2O >½ | 0.1648 Å |
0.036 Å |
| < a > |
4.4703 Å |
4.4969 Å |
| < b > |
7.7475 Å |
7.7889 Å |
| < c > |
7.2867 Å |
7.3211 Å |
| < V > |
31.55 Å3 |
32.05 Å3 |
The results for the (H2O)n clusters are also in good agreement with the available experimental and theoretical values:
| ROO (Å) | EBind (kcal/mol) | |||
|
n
|
MP2 |
Model Potential |
MP2 |
Model Potential |
|
2
| 2.907 | 2.906 |
-5.2 | -5.1 |
|
4
| 2.743 | 2.737 |
-28.6 | -29.0 |
|
6
| 2.717 | 2.728 |
-45.7 | -45.9 |
References
- E. Batista, Doctoral Dissertation, University of Washington.
- V. F. Petrenko and R. W. Whitworth, Physics of Ice, (1999, Oxford University Press, New York).