van der Waals density functional study of energetic, structural, and vibrational properties of small water clusters and ice Ih

We present results for a density functional theory study of small water clusters and hexagonal ice I-h, using the van der Waals density functional (vdW-DF). In particular, we examine energetic, structural, and vibrational properties of these systems. Our results exhibit excellent agreement with both experiment and quantum-chemistry calculations and showa systematic and consistent improvement over standard exchange-correlation functionals-making vdW-DF a promising candidate for resolving longstanding difficulties with density functional theory in describing water. In addition, by comparing our vdW-DF results with quantum-chemistry calculations and other standard exchange-correlation functionals, we shed light on the question of why standard functionals often fail to describe these systems accurately.