Energies Of Water Clusters Research Articles

Water clusters to nanodrops: a tight-binding density functional study

We predict structures and energies of water clusters containing up to 100 waters with tight-binding density functional theory (DFTB). A per-hydrogen-bond energy correction is found to correct for systematic errors in the DFTB cluster energies. We compare the DFTB structures and energies to density functional theory (DFT) calculations and to the most accurate wave function theoretical (WFT) values available (ranging from coupled-cluster theory to second-order perturbation theory). After including the simple hydrogen bond correction, we achieve a root-mean-square difference of less than one kcal mol(-1) with the best estimates. As DFTB optimizations are orders of magnitude faster than DFT or canonical MP2, it is apparent that DFTB is a very practical method for calculating large water cluster structures and, with the hydrogen bond correction, also energies.

Accurate Energies and Structures for Large Water Clusters Using the X3LYP Hybrid Density Functional

AbstractFor Abstract see ChemInform Abstract in Full Text.

Accurate Energies and Structures for Large Water Clusters Using the X3LYP Hybrid Density Functional

We predict structures and energies of water clusters containing up to 19 waters with X3LYP, an extended hybrid density functional designed to describe noncovalently bound systems as accurately as covalent systems. Our work establishes X3LYP as the most practical ab initio method today for calculating accurate water cluster structures and energies. We compare X3LYP/aug-cc-pVTZ energies to the most accurate theoretical values available (n = 2−6, 8), MP2 with basis set superposition error (BSSE) corrections extrapolated to the complete basis set limit. Our energies match these reference energies remarkably well, with a root-mean-square difference of 0.1 kcal/mol/water. X3LYP also has ten times less BSSE than MP2 with similar basis sets, allowing one to neglect BSSE at moderate basis sizes. The net result is that X3LYP is ∼100 times faster than canonical MP2 for moderately sized water clusters.