Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland.
J Chem Phys. 2010 Aug 14;133(6):064503. doi: 10.1063/1.3447701.
Using molecular dynamics (MD) simulations, the spectroscopy and dynamics of malonaldehyde is investigated. To this end, the recently proposed molecular mechanics with proton transfer (MMPT) potential is generalized to nonlinear hydrogen bonds. The calculated properties for malonaldehyde in both gas and condensed phases, including equilibrium geometries, infrared spectra, tunneling splittings, and hydrogen transfer rates, compare well with previous experimental and computational works. In particular, by using a harmonic bath averaged (HBA) Hamiltonian, which is based on a reaction path Hamiltonian, it is possible to estimate the tunneling splitting in an efficient manner. It is found that a zero point corrected barrier of 6.7 kcal/mol and effective masses of 1.234 (i.e., 23.4% larger than the mass of a physical H-atom) and 1.117 (for the physical D-atom) are consistent with the measured splittings of 21.6 and 2.9 cm(-1), respectively. The HBA Hamiltonian also yields a pair of hydrogen transfer fundamentals at 1573 and 1267 cm(-1), similar to results obtained with a reaction surface Hamiltonian on a MP2/6-31G(**) potential energy surface. This amounts to a substantial redshift of more than 1000 cm(-1) which can be rationalized by comparison with weakly (HCO(+): rare gas) and strongly (H(2)O-H(+)-OH(2)) proton-bound systems. Hydrogen transfer rates in vacuum and water were determined from the validated MMPT potential and it is found that the solvent enhances the rate by a factor of 5 at 300 K. The rates of 2.4/ns and 10/ns are commensurate with previous density functional tight binding ab initio MD studies.
利用分子动力学（MD）模拟，研究了丙二醛的光谱和动力学。为此，将最近提出的质子转移分子力学（MMPT）势扩展到非线性氢键。在气相和凝聚相下，计算得到的丙二醛的性质，包括平衡几何形状、红外光谱、隧道分裂和氢转移速率，与以前的实验和计算工作都很好地吻合。特别是，通过使用基于反应路径哈密顿量的谐和浴平均（HBA）哈密顿量，可以有效地估计隧道分裂。结果发现，零点修正势垒为 6.7 kcal/mol，有效质量为 1.234（即比物理 H-原子的质量大 23.4%）和 1.117（对于物理 D-原子），与测量的分裂值 21.6 和 2.9 cm(-1)分别一致。HBA 哈密顿量还产生了一对氢转移基频，在 1573 和 1267 cm(-1)处，与在 MP2/6-31G（**）势能面上使用反应表面哈密顿量得到的结果相似。这相当于超过 1000 cm(-1)的显著红移，可以通过与弱（HCO(+):稀有气体）和强（H(2)O-H(+)-OH(2)）质子束缚体系进行比较来合理化。从验证的 MMPT 势中确定了真空和水中的氢转移速率，结果发现溶剂在 300 K 时将速率提高了 5 倍。2.4/ns 和 10/ns 的速率与以前密度泛函紧束缚从头算 MD 研究相符。
