We recently proposed a real-time simulation method of nuclear and electron wave packet molecular dynamics (NEWPMD) based on wave functions of hydrogen molecules composed of nuclear and electron WPs. Non-empirical intra- and intermolecular interactions of non-spherical hydrogen molecules were explicitly derived and a long-range dispersion force between hydrogen molecules was successfully derived. Nuclear quantum effects (NQEs) such as nuclear delocalization and zero-point energy were non-perturbatively taken into account. The developed NEWPMD method can be applied to various condensed hydrogen systems from a gas-phase to a high-pressure solid phase at feasible computational cost, providing intuitive understandings of real-time dynamics of each hydrogen molecule including H-H bond vibration, molecular orientations and librational motions. We will report the demonstrations not only in liquid hydrogens but also in solid and supercooled hydrogens which exhibited strong NQEs and thus anomalous static and dynamic properties.
Quantum effect is manifest for hydrogen atoms on surfaces as well as for those in solution and solids. The excited states of a hydrogen atom directly adsorbed on metal surfaces are beyond the diffusion barrier, thus being delocalized to the next sites, and even spread over the entire surface in the low-coverage limit. In addition, water and hydroxyl group on the surfaces show significant quantum effect, due to tunneling and zero-point motion of the hydrogen atom. We briefly review some experimental and theoretical studies that revealed the quantum effect of the hydrogen atom on the surfaces.
Focusing on the OH−(H2O)2–4 clusters, we have theoretically studied the strongly red shifted ionic hydrogen bond (IHB) OH stretching vibration of water molecules directly bound to the hydroxide. Our calculations show that a systematic blue shift of the IHB OH peak is observed with the increase in the number of water molecules in the first solvation shell. Furthermore, we showed that the vibrational signature of the four coordinated hydroxide for OH−(H2O)4 will be observed in the 2800–3200 cm−1 range.
We analyzed the rotational constants of CH3O and CD3O by using the multi-component molecular orbital method, which takes into account the quantum effect of proton and deuteron directly. We clearly observed the difference in C–H and C-D bond lengths due to the anharmonicity of the potential. The rotational constants of CH3O and CD3O based on the optimized structures including H/D geometrical isotope effect showed good agreement with the experimental value. We found that the geometrical changes induced by the H/D isotope effect influence the spectroscopic properties, such as rotational constants.
High Performance Computerで効率の高いシミュレーションを実行できる，分子科学計算ソフトウェアNTChemと経路積分分子動力学(PIMD)法を統合した階層的並列プログラムプラットフォームを用いることにより，低障壁水素結合(LBHB)の存在が示唆されているperiplasmic phosphate binding protein (PPBP)のモデル分子である酢酸－リン酸アニオンクラスターの分子間水素結合における原子核の量子揺らぎの効果を明らかにした．モデル分子における一つの水素結合を形成する配置を解析したところ，原子核を古典的な質点で取り扱った古典シミュレーションでは，プロトンは水素結合の両端に局在化し，通常の水素結合と同様の振る舞いを示した．一方，原子核の量子揺らぎの効果を取り込んだ量子シミュレーションでは，プロトンが水素結合の中央に存在する確率が高くなった．酢酸－リン酸アニオンクラスターの分子間水素結合は，LBHBと同じような傾向を示した．