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March 2006

The Flexible, Polarizable, Thole-type Interaction Potential for Water (TTM2-F) Revision (2.1)

In May 2005, we posted a highlight on research into the properties of water, It's all in the water. Since then, PNNL researchers have continued to refine the computer code they developed, and have published revision 2.1.

In revision (2.1) of the flexible, polarizable, Thole-type interaction potential for water (TTM2-F), the following changes were implemented with respect to the original version [C. J. Burnham and S. S. Xantheas, J. Chem. Phys. 116, 5115 (2002)]:

(a) The inverse (12-10-6) polynomial, which describes the long-range van der Waals interactions between the Oxygen atoms as well as the repulsive interactions at short O-O separations, has been modified to include an additional exponential term according to

Water potential

where r stands for the intermolecular O-O separation. The parameters A, B, C, D and E for both potentials are given in Table 1 and the new function of eq. (1) is plotted in Figure 1.

Water potential graphic

Table 1. Parameters of the pair-wise additive part. A, B and C are common for the TTM2-F and TTM2.1-F potentials.

Figure 1. The pairwise additive part for the O-O interaction for the TTM2.1-F (solid line) and the TTM2-F (dashed line) potentials. The two potential forms differ only in the short range while, at larger separations the inner graph clearly shows that the two potentials coincide.

(b) The charges qa on the charge bearing sites (H1, H2, M) are determined from the charges qa on the nuclear sites (which are taken from the Partridge-Schwenke Dipole Moment Surface) according to

The revised version (TTM2.1-F) of the potential correctly describes the individual water molecular dipole moment and alleviates problems arising at short intermolecular separations which can be sampled in the course of molecular dynamics and Monte Carlo simulations of condensed environments.

We report the radial distribution functions, average energy, internal geometry and dipole moment in the liquid as well as the density, dielectric constant and self-diffusion coefficient at T=300 K from (NVT) and (NPT) classical molecular dynamics simulations using the revised version of the potential, see GS Fanourgakis and SS Xantheas, Journal of Physical Chemistry A 110(11):4100-4106 (2006).

Notice: This computer software was prepared by Battelle Memorial Institute, hereinafter the Contractor, under Contract No. DE-AC05-76RL0 1830 with the Department of Energy (DOE). All rights in the computer software are reserved by DOE on behalf of the United States Government and the Contractor as provided in the Contract. NEITHER THE GOVERNMENT NOR THE CONTRACTOR MAKES ANY WARRANTY, EXPRESS OR IMPLIED, OR ASSUMES ANY LIABILITY FOR THE USE OF THIS SOFTWARE. This notice including this sentence must appear on any copies of this computer software. Download (tar.gz file 37kb) a Fortran-90 subroutine with the new version of the TTM2.1-F potential (energies and gradients).

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