Molecular dynamics simulation based on the multi-component molecular orbital method: Application to H ₅O ₂ ⁺, D ₅O ₂ ⁺, and T ₅O ₂ ⁺

We propose a molecular dynamics (MD) method based on the multi-component molecular orbital (MC-MO) method, which takes into account the quantum effect of proton directly, for the detailed analyses of proton transfer in hydrogen bonding system. The MC-MO based MD (MC-MO-MD) method is applied to the basic structures, H ₅O ₂ ⁺ (called "Zundel ion"), and its isotopomers (D ₅O ₂ ⁺ and T ₅O ₂ ⁺). We clearly demonstrate the geometrical difference of hydrogen bonded O ^⋯O distance induced by H/D/T isotope effect because the O ^⋯O in H-compound was longer than that in D- or T-compound. We also find the strong relation between stretching vibration of O ^⋯O and the distribution of hydrogen bonded protonic wavefunction because the protonic wavefunction tends to delocalize when the O ^⋯O distance becomes short during the dynamics. Our proposed MC-MO-MD simulation is expected as a powerful tool to analyze the proton dynamics in hydrogen bonding systems.