Extended ab initio quantum mechanical/molecular mechanical molecular dynamics simulations of hydrated Cu2+

Abstract

Copper(II) was used as a model system to investigate the relevance of including the full second hydration shell in ab initio treatment while describing hydrated ions in hybrid quantum mechanical/molecular mechanical molecular dynamics (QM/MM MD) simulations. Three different simulation techniques were applied (Hartree–Fock, B3LYP, and resolution of the identity density functional theory) to find a good compromise between accuracy and simulation speed. To discuss details of the hydration structure radial distribution functions, coordination number distributions and various angular distributions have been used. Dynamical properties such as vibrational motions of water molecules and ion–oxygen stretching motions were investigated using approximative normal coordinate analyses. QM/MM MD simulations offer a detailed time picture of the dynamic Jahn–Teller effect of ${\mathrm{Cu}}^{\text{2+}}$ showing short-term as well as long-term distortions to occur within <200 fs and 2–3 ps. The results prove that for transition metal ions such as ${\mathrm{Cu}}^{\text{2+}}$ the inclusion of the second shell into the ab initio treated region can be of decisive importance for obtaining accurate results and that such simulations can offer new insights into chemical dynamics on the picosecond scale.