Abstract
Water is ubiquitous on our planet and plays an essential role in many
chemical and biological processes. Accurate models for water are
crucial in understanding, controlling and predicting the physical and
chemical properties of complex aqueous systems. Over the last few
years we have been developing a molecular-level based approach for a
macroscopic model for water that is based on the explicit description
of the underlying intermolecular interactions between molecules in
water clusters. In the absence of detailed experimental data for small water
clusters, highly-accurate theoretical results are required to validate
and parameterize model potentials. As an example of the
benchmarks needed for the development of accurate models for the
interaction between water molecules, for the most stable structure of
(H$_2$O)$_{20}$ we ran a coupled-cluster calculation on the ORNL's
Jaguar petaflop computer that used over 100 TB of memory for a
sustained performance of 487 TFLOP/s (double precision) on 96,000
processors, lasting for 2 hours. By this summer we will have studied
multiple structures of both (H$_2$O)$_{20}$ and (H$_2$O)$_{30}$ and
completed basis set and other convergence studies and anticipate
the sustained performance rising close to 1 PFLOP/s.