ALCF Science 1 - Argonne National Laboratory

10
EARLY SCIENCE PROGRAM
Chemistry
High-Accuracy Predictions of the Bulk Properties of Water
Among the ab initio methods, second-order perturbation theory (MP2)
predicts highly accurate structures and relative energies for water
clusters. Researchers will carry out molecular dynamics simulations
of water at the MP2 level. However, full MP2 calculations of even
modest-sized water clusters are far too time-consuming for dynamical
simulations, even on the next-generation Blue Gene. Therefore, a key
element of the current approach will be the use of MP2 in conjunction
with the Fragment Molecular Orbital (FMO) method. Compared with
today’s calculations, researchers will determine the bulk properties
at higher levels of accuracy using larger basis sets, larger embedded
clusters, and longer dynamics simulations, as permitted by the greater
computational capacity available with the Blue Gene. They will target
the following bulk properties of water: structure, density, refractive
index, diffusion constant, free energy, heat capacity, dielectric constant,
vaporization enthalpy, isothermal compressibility, and thermal
expansion coefficients. The final eight properties are more difficult to
obtain than the first two. While Blue Gene/P gives good estimates,
the greater capacity of the next-generation Blue Gene will be critical
to establishing convergence of these properties with respect to
theory, basis set, cluster size, and simulation length. There have been
conflicting reports in the literature about the relevance of “chain”
or”ring” networks in water. The high-accuracy simulations on the nextgeneration
Blue Gene will help settle this argument about the structure
of liquid water.
Early Science Program
Allocation:
2 Million Hours
Contact Mark Gordon
Iowa State University | mark@si.msg.chem.iastate.edu