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Although metal nanomaterials with unconventional phases have attracted extensive attention, the lack of information on the characteristics of metal polytypes hinders the development of related research. In this work, the energetics of nonequivalent polytypes for bulk face‐centered cubic (Li, Al, Ca, Cu, Sr, Rh, Pd, Ag, Ir, Pt, Au, and Pb) and hexagonal close‐packed metals (Be, Na, Mg, Sc, Ti, Zn, Cd, Y, Zr, Tc, Ru, Hf, Re, Os, and Tl) is systematically reported. For each metal, the structural properties and energies for its polytypes with up to the periodic stacking length of L = 10 is obtained by DFT calculation. The variation tendency of the energy differences between 3C and 2H polytypes is summarized in the Periodic Table of Elements. Generally, the ratio c/(La) increases when metal crystals except Ir, Rh, Zn, and Cd leave away from their ground‐state structure. It is found that the energy difference between polytypes originates from various interactions between the two types of atomic layers: the k layer and the h layer. The work is helpful to understand not only the structural transitions in bulk metals, such as Li, Na, Sr, Ti, Al, Pb, Y, Re, and Tl, but also the evolutions of Au nanomaterials. [ABSTRACT FROM AUTHOR]

In this paper, the spin ladder consisting of two antiferromagnetic Heisenberg legs is investigated by means of the density matrix renormalization group method with its matrix product state form. The energy density and bipartite entanglement measured by concurrence are calculated, the effects of interleg couplings and open boundary condition on entanglement distributions are discussed in detail when the interleg couplings are ferro- and antiferromagnetic, respectively. We found that the entanglements are mainly distributed in legs and diagonals when the interleg couplings are ferromagnetic and in rungs when the couplings are antiferromagnetic. Furthermore, the intraleg entanglements are more affected by the dimerization caused by open boundary than interleg ones. Specifically, that dimerization will be weakened by the interleg couplings, and the entanglements are distributed more uniformly. [ABSTRACT FROM AUTHOR]

As to the prototypical realization of the famous Mermin–Wagner theorem, two dimensional Heisenberg ferromagnets (2D HFMs) are expected to have no static order at finite temperatures [N. D. Mermin and H. Wagner, Phys. Rev. Lett., 1966, 17, 1133]. However, a perfect 2D HFM with negligible inter-layer exchange is still lacking, impeding studies of its novel properties. Here we report the synthesis, structure, and properties of a new metal–organic single crystal piperazinediium tetrabromocuprate ((C4H12N2)CuBr4, PTBC). The Cu2+ spins form perfect 2D layers which are well separated by organic ligands. Single crystal electron paramagnetic resonance (EPR) and magnetic susceptibility measurements reveal that PTBC is a highly isotropic Heisenberg ferromagnet with a strong intra-layer ferromagnetic exchange J/kB = 31.34(6) K (H‖ab) and 36.54(17) K (H⊥ab). However, it does not order down to 2 K, indicating the negligible inter-layer exchange J′ and ultra-small R ratio (R = J′/J) below 6 × 10−28. This is the smallest R ratio ever reported for a 2D HFM. These results imply that PTBC is by far the best realization of a 2D HFM system. Moreover, the typical single crystal size is as large as 20 mm × 20 mm × 3 mm, making it suitable for studying the magnetic dynamics of a 2D HFM by probes such as inelastic neutron scattering. [ABSTRACT FROM AUTHOR]

In the present work, a comprehensive theoretical investigation on the excited state properties of the isomorphic emissive RNA nucleobase analogues, namely tzA, tzG, tzC, and tzU, was performed. Vertical transition energies are determined with the time-dependent density functional theory method at both the B3LYP and CAM-B3LYP levels using the 6-311++G(d,p) basis set. The nature of the low-lying singlet excited states is discussed and the results are compared with the findings from experiment and those for thieno analogues and natural bases. In gas phase, it was found that the S1 state is ππ* in nature for all the tz-bases except for tzA, for which the S1 state is predicted to be nπ* in nature with the ππ* state being the S2. While in water solution, the S1 state for all tz-bases are predicted to be ππ* dominated by the configuration HOMO→LUMO. Compared with natural bases, the lowest ππ* states are about 0.85-1.22 eV red-shifted. When compared with thieno analogues, it is interesting to note that the S1 state (ππ*) transition energies of the two counterparts from the two alphabets are nearly equal due to the very little differences of their HOMO-LUMO gaps. In addition, it was found that the hydration + PCM model can perfectly reproduce the photophysical properties of the tz-bases since the calculated excitation maxima and fluorescence are in good agreement with the experimental data. The microenvironment effects of linking to ribose, base pairing, and further hydration of base pairs were also studied. [ABSTRACT FROM AUTHOR]

Unnatural nucleobases are under intense research due to their widespread applications in nucleic acids research. In this work, four new thieno‐expanded purine analogs comprising ttzA, tthA, ttzG, and tthG were computationally designed based on the isomorphic tz‐ and th‐bases. These base analogs can also be seen as modified derivatives of the previously reported tricyclic purine analogs (ttA and ttG). The structural, electronic, and photophysical properties are studied by means of DFT and TDDFT calculations. We find out that these new bases can form stable Watson‐Crick base pairs with natural counterparts, thus potentially mimicking natural nucleobases in DNA/RNA duplexes. Calculations reveal that these bases have smaller AIPs and HOMO‐LUMO gaps than natural ones, suggesting that they are candidates for applications in nanowire technology. Particularly, the photophysical properties were explored, and the results are compared with those for tz‐, th‐, and tt‐bases. The nature of the low‐lying excited states is discussed, and analyses reveal that the thiophene‐homologation would not change excitation maxima of thA and tzA, while it will result in large red‐shifts of those of thG and tzG. Meanwhile, thiophene insertion has relatively larger influences on the emissions thA and tzG, for which the fluorescence was 37 nm blue‐shifted and 19 nm red‐shifted, respectively. Taking these new bases as derivatives of ttA and ttG, it was found that the modifications would result in large red‐shifts of both the excitation maxima and the fluorescence. The effects of water solution and base paring on the phtotophysical properties were also considered. Four new thieno‐expanded purine analogs are computationally designed based on the isomorphic th‐ and tz‐bases. The structural, electronic, and photophysical properties are studied by means of DFT and TDDFT calculations. Micro‐environment effects of hydration, base pairing, and further hydration of base pairs on photophysical properties are examined and the results are compared with their parental bases. The predictions may be helpful for experimental design of novel nucleobase analogs. [ABSTRACT FROM AUTHOR]

In this paper, the quantum entanglement (concurrence) of one-dimensional antiferromagnetic XXZ spin system with alternating nearest-neighbor interactions is studied by means of the density matrix renormalization group method with matrix product state form. The ground-state energy, long-distance entanglement and entanglement distribution are calculated, and the effects of alternating interactions, anisotropy and open boundary condition on them are discussed. It is found that the alternating interactions favor the generation and development of long-distance entanglement, while anisotropy inhibits that. For the entanglement distribution of the system, it is also found that the alternating interactions and open boundary condition induce the dimerization on odd and even bonds, respectively, while anisotropy always suppresses this behavior. Furthermore, both nearest-neighbor and long-distance entanglements are converged to certain values with increasing system size. • Long-distance entanglement is strengthened by alternating interactions. • OBC and alternating couplings make the dimerization on odd and even bonds, respectively. • Anisotropy always inhibits dimerization caused by OBC or alternating interactions. [ABSTRACT FROM AUTHOR]

The diffusion of passing over the saddle point of a three-dimensional quadric potential energy surface was studied by analytically solving a set of coupled generalized Langevin equations. An accurate expression of the passing probability was obtained. The effect of the coupling between different degrees of freedom which is represented by the off-diagonal elements of the inertia, friction and potential-curvature tensors was analyzed in detail. It is found that some of the coupling have great influence on the diffusion process, while others not. The combination of them results in an optimal injecting direction of the diffusing particles, revealing an optimal three-dimensional diffusion path. • Off-diagonal elements of the tensors in the generalized Langevin equation were all recovered. • Optimal path of diffusion on the three-dimensional potential energy surface was determined. • Two angles were defined to determine the optimal path of diffusion of Brownian particles. [ABSTRACT FROM AUTHOR]

We explore the phase diagram, structures, electron properties, and potential superconductivity of the K-P system at pressures of up to 200 GPa through unbiased structure searching techniques and first-principles calculations. Five stable chemical stoichiometries (K 4 P, K 3 P, K 2 P, KP, and KP 2 ) have been theoretically predicted. In particular, P 2 units or P-chains are uncovered in K 2 P, KP, and KP 2 compounds with the existence of covalent bonds by analyzing the electron localization functions. And the Bader analysis demonstrates that charges transfer from K atoms to P atoms. Electron-phonon calculations show that the T c of metallic I4/mmm-KP 2 is 22.01 K at 5 GPa. The investigating of the K-P system is in favor of understanding the crystal structures and corresponding properties of potassium phosphides, which also give a strong motivation to search and design new superconductor materials in other phosphides.