No abstract

Ternary metal hydrides play an essential role in the search for conventional high‐temperature superconductors because they can be synthesized under mild conditions and recovered at ambient pressure. It has been widely accepted that the electronic structure, metallization pressure, and superconducting behavior of binary hydrides can be adjusted effectively by doping, replacing, or introducing a new element. In this work, yttrium hydrides were chosen as parent hydrides, while scandium was considered the doping element to perform systematical crystal structure searches on the Sc‐Y‐H system under pressure. A new ternary hydride ScYH6 with a Pm‐3 structure (cP8) was found below 150 GPa according to Particle Swarm Optimization calculations, and then, a P4/mmm phase (tP8) becomes favorable from 150 GPa. Importantly, cP8‐ScYH6 is dynamically stable under pressure as low as 0.01 GPa with a superconducting temperature (Tc) of 32.110 K for Coulomb pseudopotential μ* = 0.13, indicating that ternary hydrides are promising candidates in the search for superconductors that can be synthesized under mild conditions in hydrogen‐rich materials. The analysis using the “triangle straight‐line method”, compared with enthalpy difference calculations, showed that the most reasonable synthesis pathway of ScYH6 is ScH3 + YH3 → ScYH6 in the whole pressure regime studied in this work. The Tc of ScYH6 has a linear relationship with pressure up to 52.907 K under 200 GPa. The lattice dynamical calculations demonstrate that the H atoms in both cP8 and tP8 structures make crucial contributions to the superconducting behavior of ScYH6. These findings can further reveal the influence of doping, replacing, and introducing element on the superconducting behavior of binary hydrides.

Molecular dynamics simulation was applied to investigate the sensitivities of perfect and defective RDX (cyclotrimethylene trinitramine) crystals, as well as their PBXs (polymer-bonded explosives) with the polymeric binder F(2311), in the NPT (constant number of particles, constant pressure, constant temperature) ensemble using the COMPASS force field. Five kinds of defects-two dislocations, one vacancy, and two types of doping-were considered separately. The bond length distribution and the maximum (L (max)) and average (L (ave)) bond lengths of the N-NO(2) trigger bonds in RDX were obtained and their relationships to the sensitivities of RDX and PBXs are discussed. L (max) was found to be an important structural parameter for judging the relative sensitivity, and defects were observed to have little effect on the sensitivities of PBXs, due to the strong desensitizing effect of the polymer F(2311).

Influence of static electric field in biological cells causes electroporation, which results in the increase of permeability of the cells and phospholipid bilayer. However, the precise mode of action of electric fields on phospholipid bilayer and their quantum mechanics are still unclear. Therefore, to understand the quantum-based biological effect, we aimed to study two-dimensional infrared (2D-IR) spectra-adopted quantum mechanics/molecular mechanics (QM/MM) simulations under the influence of static electric fields on Phosphorylcholine, an important component in phospholipid membrane. Initially, QM/MM studies were performed under the influence of electric field, ranging from −1.543 to 1.028 V/nm. A multilayer ONIOM model (in combination with DFT/B3LYP/6-31G [d, p] and DREIDING force fields) was used to obtain 2D-IR simulated spectra to calculate electrostatic interaction in the biological system. The results demonstrated that the phosphate group played an important role on α-rotation in LUMO and the chlorine atom had a major contribution in HOMO. In addition, decreased number of hydrogen bonds demonstrated that uncoupling reaction of the P-O stretching vibrations while the electric field was −1.542 V/nm. Moreover, we observed that the electric field is −1.028 V/nm, there is no rotational isomerization in phosphorylcholine. We concluded that the static electric fields significantly affect the anharmonic frequencies, vibration coupling and the structure of the phosphorylcholine. K E Y W O R D S2D-IR, anharmonicity, electric field, rotational isomerization, vibration coupling

There is no doubt that electric fields of a specific frequency and intensity could excite certain vibrational modes of a macromolecule, which alters its mode coupling and conformation. Motivated by recent experiments and theories, we study the mode coupling between the Fe–CO mode and CO-stretch mode and vibration energy transfer among the active site and proteins in carboxyhemoglobin (HbCO) under different electric fields using the quasi-static two-dimensional infrared spectra. This study uses iron–porphyrin–imidazole–CO and two distal histidines in HbCO as the subsystem. The potential energy and dipole moment surfaces of the subsystem are calculated using an all-electron ab initio (B3LYP-D3­(BJ)) method with the basis set Lanl2dz for the Fe atom and 6-31G­(d,p) for C, H, O, and N atoms. Although the subsystem is reduced dimensionally, the anharmonic frequency and anharmonicity of the CO-stretch mode show excellent agreement with experimental values. We use the revealing noncovalent interaction method to confirm the hydrogen bond between the Hε atom of the His63 and the CO molecule. Our study confirms that the mode coupling between the Fe–CO mode and CO-stretch mode does not exist when the subsystem is free of electric field perturbation, which is coupled when the electric field is −0.5142 V/nm. In addition, with the increases of distance between the active site and the His92, there is no vibrational energy transfer between them when the electric field is 1.028 V/nm. We believe that our work could provide new ideas for increasing the dissociation efficiency of the Fe–CO bond and theoretical references for experimental research.