A force field for liquid water including polarization effects has been constructed using an artificial neural network (ANN). It is essential to include a many-body polarization effect explicitly into a potential energy function in order to treat liquid water which is dense and highly polar. The new potential energy function is a combination of empirical and nonempirical potentials. The TIP4P model was used for the empirical part of the potential. For the nonempirical part, an ANN with a back-propagation of error algorithm (BPNN) was introduced to reproduce the complicated many-body interaction energy surface from ab initio quantum mechanical calculations. BPNN, described in terms of a matrix, provides enough flexibility to describe the complex potential energy surface (PES). The structural and thermodynamic properties, calculated by isobaric-isothermal (constant-NPT) Monte Carlo simulations with the new polarizable force field for water, are compatible with experimental results. Thus, the simulation establishes the validity of using our estimated PES with a polarization effect for accurate predictions of liquid state properties. Applications of this approach are simple and systematic so that it can easily be applied to the development of other force fields besides the water-water system.
Bibliographical noteFunding Information:
We thank Drs C. Czaplewski, A. Liwo and W.J. Wedemeyer for helpful discussions about Monte Carlo simulations. This work was supported by grants from the US National Science Foundation (MCB00-03722). The computations were carried out on the IBM SP2 supercomputer of the Cornell Theory Center (CTC), the CTC's Advanced Cluster Computing Consortium, and at the San Diego Supercomputer Center.
All Science Journal Classification (ASJC) codes
- Analytical Chemistry
- Organic Chemistry
- Inorganic Chemistry