Direct ab initio dynamics studies of proton transfer in hydrogen‐bond systems

We present systematic direct ab initio dynamics studies of proton transfer in hydrogen‐bond systems using the tautomerization in gas phase formamidine and its monohydrated complex as model reactions. The thermal rate constants were calculated using a canonical variational transition state theory (CVT) with multidimensional semiclassical tunneling corrections within a small‐curvature ground‐state approximation. The reaction valleys were calculated at the second‐order Mo/ller–Plesset (MP2) perturbation theory, Hartree–Fock (HF) and nonlocal Becke’s half‐and‐half exchange and Lee–Yang–Parr correlation (BH&H–LYP) density functional theory (DFT) levels of theory using the 6‐31 G(d,p) basis set. For accurate rate constants, the potential energy along the minimum energy path was scaled to match the single‐point coupled cluster calculations including single and double excitations plus correction for triple excitation [CCSD(T)] at the MP2/6‐31 G(d,p) classical barrier for each reaction. In the HF rate calculations...

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