Simplified electronic-structure model for hydrogen-bonded systems: Water

An approximate ab initio electronic dynamics technique has been developed to describe the weak interactions between molecules within hydrogen bonded systems. This technique is developed to concentrate on the intermolecular binding, since in thses sytems the intramolecular interactions are relatively unchanged. These weak intermolecular interactions are described using a linear combination of atomic orbitals formalism, and consideration of the expansion of the overlap S between molecules up to order S². The method is especially designed to perform large-scale molecular-dynamics simulations of interacting closed-shell molecules explicitly including the microscopic quantum effects. As an application of the theory, several molecular-dynamical quenched simulations of the H₂O dimer and trimer systems have been performed. To demonstrate the method's efficiency, a long 5-ps (25 000 steps) simulation of a H₂O trimer system was carried out. Comparisons with other first-principles calculations and experimental data show that the theory presented here suitably describes the dimer and trimer systems. The method is transferable to other molecular systems, with its main advantage being its computational simplicity.