Integrating ferromagnetism and ferroelectricity in an iron chalcogenide monolayer: a first-principles study.

Two-dimensional (2D) ferro-type materials have received great attention owing to the remarkable polarization effect in optoelectronics and spintronics. Using the first-principles method, the coupling between ferromagnetism and ferroelectricity is investigated in a multiferroic Janus 1T-FeSSe monolayer, which has a strong Stoner ferromagnetic ground state. The magnetic anisotropy energy (MAE) is apparently impacted by the out-of-plane asymmetry donated ferroelectricity, which is reflected by the asymmetry of the Z-MAE image. The easy magnetization axis of Janus FeSSe is the +y axis with a large MAE of 0.59 meV, rooting in unpaired d electrons of Fe atoms. The transformation of band splitting and Fermi surface can be effectively engineered by different magnetic polarization directions. The ferromagnetic (FM) coupling of the FeSSe monolayer is very robust under external strain within the range of -6% to 6%, while the strength of magnetic moment of Fe atoms and polarization are easily strain-engineered, the intrinsic mechanism of which can be elaborated by the GKA rules that depend on angles and distances. This multiferroic FeSSe monolayer provides a new platform for exploring the coupling of 2D ferromagnetism and ferroelectricity and designing low-dimensional multiferroic electronics.

Insights into the functional divergence of the haloacid dehalogenase superfamily from phosphomonoesterase to inorganic pyrophosphatase.

The evolution of enzyme catalytic structures and mechanisms has drawn increasing attention. In this study, we investigate the functional divergence from phosphomonoesterase to inorganic pyrophosphatase in the haloacid dehalogenase (HAD) superfamily. In this study, a series of models was constructed, and calculations were performed by using density functional theory with the B3LYP functional. The calculations suggest that in most HAD members, the active-site structure is unstable due to the binding of the substrate inorganic pyrophosphate (PPi), and reactions involving PPi cannot be catalyzed. In BT2127, which is a unique member of the HAD superfamily, the Mg2+-coordinating residues Asn172 and Glu47 play a role in stabilizing the active-site structure to adapt to the substrate PPi by providing much stronger coordination interactions with the Mg2+ ion. The calculation results suggest that Asn172 and Glu47 are crucial in the evolution of the inorganic pyrophosphatase activity in the HAD superfamily. Our study provides definitive chemical insight into the functional divergence of the HAD superfamily, and helps in understanding the evolution of enzyme catalytic structures and mechanisms.

Clarification of the Molecular Doping Mechanism in Organic Single-Crystalline Semiconductors and their Application in Color-Tunable Light-Emitting Devices.

Organic single-crystalline semiconductors with long-range periodic order have attracted much attention for potential applications in electronic and optoelectronic devices due to their high carrier mobility, highly thermal stability, and low impurity content. Molecular doping has been proposed as a valuable strategy for improving the performance of organic semiconductors and semiconductor-based devices. However, a fundamental understanding of the inherent doping mechanism is still a key challenge impeding its practical application. In this study, solid evidence for the "perfect" substitutional doping mechanism of the stacking mode between the guest and host molecules in organic single-crystalline semiconductors using polarized photoluminescence spectrum measurements and first-principles calculations is provided. The molecular host-guest doping is further exploited for efficient color-tunable and even white organic single-crystal-based light-emitting devices by controlling the doping concentration. The clarification of the molecular doping mechanism in organic single-crystalline semiconductor host-guest system paves the way for their practical application in high-performance electronic and optoelectronic devices.

Evolution of phosphotriesterase activities of the metallo-ß-lactamase family: A theoretical study.

Metallo-ß-lactamase (MßL) is a eubacterial zinc metallo-hydrolase superfamily. Despite their well-known lactamase activities, MßL family members also have the ability to catalyze phosphotriester hydrolysis with different phosphotriesterase activities. In the present study, based on crystal structure comparisons of the related MßL members, a series of models was constructed and calculated using the density functional theory (DFT) method to explore the relationship between active-site changes and phosphotriesterase activities. These calculations show that the energetic barriers for phosphotriesterase activity are considerably reduced due to active-site differences, which describes an evolutionary trend for the development of phosphotriesterase activity in the MßL superfamily. The key event is the appearance of a specialized and negatively charged residue bridging both zinc ions, which plays the two important roles of maintaining charge balance and stabilizing the binuclear active-site structure. This pathway is also consistent with the evolutionary relationships determined by phylogenetic tree analysis using complete residue sequences. Our studies provide the first methodology to explore the development of a new enzyme activity within a superfamily, and to shed new light on understanding the catalytic mechanism from an evolutionary perspective.

Electronic properties of tricoordinated phosphorus in hexagonal phosphininium compounds and molecular aromaticity.

Calculations with B3LYP within quantum chemical density functional theory have been carried out for 1-H-phosphininium cation and a series of 1-R-phosphininium molecules (R=cyclopentadiene, alpha and beta pyrroles, alpha and beta phosphole, C5BH5-- and CH2--). The negative nuclear-independent chemical shift values and the positive aromatic stabilization energies confirm that they are aromatic compounds. In particular, the 1-H-phosphininium cation even exhibits stronger aromatic character than the well-known aromatic phosphinine. The aromatic substituents have strong capability to attract electrons. It is the conjugation and aromaticity that keeps the stability and conformations of the molecules investigated. Owing to the perturbation of the aromatic substituted groups, the predicted large T values and the enlarged HOMO-LUMO gap of the phosphininium cation indicate that these compounds are expected in experiment.

Theoretical study on structures and aromaticities of P5(-) anion, [Ti (eta(5)-P5)]- and sandwich complex [Ti(eta(5)-P5)2]2-.

The equilibrium geometries, energies, harmonic vibrational frequencies, and nucleus independent chemical shifts (NICSs) of the ground state of P5(-) (D(5h)) anion, the [Ti (eta(5)-P5)]- fragment (C(5v)), and the sandwich complex [Ti(eta(5)-P5)2]2- (D(5h) and D(5d)) are calculated by the three-parameter fit of the exchange-correlation potential suggested by Becke in conjunction with the LYP exchange potential (B3LYP) with basis sets 6-311+G(2d) (for P) and 6-311+G(2df) (for Ti). In each of the three molecules, the P-P and Ti-P bond distances are perfectly equal: five P atoms in block P5(-) lie in the same plane; the P-P bond distance increases and the Ti-P bond distance decreases with the order P5(-), [Ti(eta(5)-P5)2]2-, and [Ti (eta(5)-P5)]-. The binding energy analysis, which is carried out according to the energy change of hypothetic reactions of the three species, predicts that the three species are all very stable, and [Ti (eta(5)-P5)]- (C(5v)), more stable than P5(-) and [Ti(eta(5)-P5)2]2- synthesized in the experiment, could be synthesized. NICS values, computed for the anion and moiety of the three species with GIAO-B3LYP, reveal that the three species all have a larger aromaticity, and NICS (0) of moiety, NICS (1) of moiety, and minimum NICS of the inner side of ring P5 plane in magnitude increase with the order P5(-), [Ti(eta(5)-P5)2]2-, and [Ti (eta(5)-P5)]-. By analysis of the binding energetic and the molecular orbital (MO) and qualitative MO correlation diagram, and the dissection of total NICS, dissected as NICS contributions of various bonds, it is the main reason for P5(-) (D(5h)) having the larger aromaticity that the P-P sigma bonds, and pi bonds have the larger diatropic ring currents in which NICS contribution are negative, especially the P-P sigma bond. However, in [Ti (eta(5)-P5)]- (C(5v)) and [Ti(eta(5)-P5)2]2- (D(5h), and D(5d)), the reason is the larger and more negative diatropic ring currents in which the NICS contributions of P-P pi bonds and P5-Ti bonds including pi, delta, and sigma bonds, especially P5-Ti bonds, are much more negative and canceled the NICS contributions of P and Ti core and lone pair electrons.