This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange–correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear–electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an “open teamware” model and an increasingly modular design.

Metallic osmium (Os) is one of the most exceptional elemental materials, having, at ambient pressure, the highest known density and one of the highest cohesive energies and melting temperatures. It is also very incompressible, but its high-pressure behaviour is not well understood because it has been studied so far only at pressures below 75 gigapascals. Here we report powder X-ray diffraction measurements on Os at multi-megabar pressures using both conventional and double-stage diamond anvil cells, with accurate pressure determination ensured by first obtaining self-consistent equations of state of gold, platinum, and tungsten in static experiments up to 500 gigapascals. These measurements allow us to show that Os retains its hexagonal close-packed structure upon compression to over 770 gigapascals. But although its molar volume monotonically decreases with pressure, the unit cell parameter ratio of Os exhibits anomalies at approximately 150 gigapascals and 440 gigapascals. Dynamical mean-field theory calculations suggest that the former anomaly is a signature of the topological change of the Fermi surface for valence electrons. However, the anomaly at 440 gigapascals might be related to an electronic transition associated with pressure-induced interactions between core electrons. The ability to affect the core electrons under static high-pressure experimental conditions, even for incompressible metals such as Os, opens up opportunities to search for new states of matter under extreme compression.

Electrochemical CO2 reduction reaction (CO2RR) to eliminate the excess CO2 and produce fuels/chemicals under mild conditions provides a sustainable way to maintain the carbon balance and alleviate the energy shortage....

The Fermi surface (FS) nesting properties of URu2Si2 are analyzed with particular focus on their implication for the mysterious hidden order phase. We show that there exist two Fermi surfaces that exhibit a strong nesting at the antiferromagnetic wavevector, Q0=(0, 0, 1). The corresponding energy dispersions fulfill the relation 1(k)=− 2(k ± Q0) at eight FS hotspot lines. The spin-orbital characters of the involved 5f states are distinct (jz=±5/2 vs. ±3/2) and hence the degenerate Dirac crossings are symmetry protected in the nonmagnetic normal state. Dynamical symmetry breaking through an Ising-like spin and orbital excitation mode with ∆jz=±1 induces a hybridization of the two states, causing substantial FS gapping. Concomitant spin and orbital currents in the uranium planes give rise to a rotational symmetry breaking.PACS numbers: 71.27.+a, 74.70.Tx At temperatures below T o =17.5 K a mysterious hidden order (HO) phase develops 1-3 in the heavy-fermion uranium compound URu 2 Si 2 , the origin of which could not be definitely established despite intensive investigations. 4The occurrence of the new, ordered phase below T o is clearly witnessed by a sharp, second order phase transition appearing in the thermodynamic and transport quantities.1,2,5,6 The appearing new electronic order is not long-range ordered (dipolar) magnetism, although a small pressure of about 0.5 GPa suffices to stabilize longrange antiferromagnetic (AF) order.7,8 Recent experimental progress succeeded to reveal particular features of the HO state, thus providing a mosaic of pieces for unraveling the HO.9-17 To explain the origin of the HO a large number of sometimes exotic theories have been proposed over a period of more than twenty years 18-27 which however could not yet provided a complete understanding (see Ref. 4 for a survey of theories).A central question concerning the nature of the HO phase is which symmetry is spontaneously broken at the HO transition. A recent torque experiment performed on very small (µm-size) single crystals measured the magnetic susceptibility in the basal a-a plane of the tetragonal unit cell.28 Okazaki et al. 28 observe rotational symmetry breaking, i.e., the off-diagonal susceptibility χ xy is nonzero in the HO phase, unlike in the normal nonmagnetic phase above T o where χ xy =0. To explain the nonzero off-diagonal susceptibility several novel models 29-31 for the HO phase have been put forward recently. The non-vanishing off-diagonal susceptibility has been ascribed to a certain type of quadrupolar order, 29 a modulated spin liquid, 30 and a spin nematic state. 31Apart from breaking of xy-symmetry in the basal plane, it recently became clear that the lattice periodicity along the c -axis in the Brillouin zone (BZ) is modified, too, in the HO phase.14,15 The body-centered tetragonal (bct) unit cell of URu 2 Si 2 in the normal state becomes doubled in the HO state, and thus becomes simple tetragonal (st), consistent with a recent prediction.23 A complete understanding of the HO state obviously require...

Quasi-solid-state Zn-air batteries are usually limited to relatively low-rate ability (<10 mA cm−2), which is caused in part by sluggish oxygen electrocatalysis and unstable electrochemical interfaces. Here we present a high-rate and robust quasi-solid-state Zn-air battery enabled by atomically dispersed cobalt sites anchored on wrinkled nitrogen doped graphene as the air cathode and a polyacrylamide organohydrogel electrolyte with its hydrogen-bond network modified by the addition of dimethyl sulfoxide. This design enables a cycling current density of 100 mA cm−2 over 50 h at 25 °C. A low-temperature cycling stability of over 300 h (at 0.5 mA cm−2) with over 90% capacity retention at −60 °C and a broad temperature adaptability (−60 to 60 °C) are also demonstrated.

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Metal-free bifunctional oxygen electrocatalysts are extremely critical to the advanced energy conversion devices, such as high energy metal-air batteries. Effective tuning of edge defects and electronic density on carbon materials via simple methods is especially attractive. In this work, a facile alkali activation method has been proposed to prepare carbon with large specific surface area and optimized porosity. In addition, subsequent nitrogen-doping leads to high pyridinic-N and graphitic-N contents and abundant edge defects, further enhancing electrochemical activities. Theoretical modeling via first-principles calculations has been conducted to correlate the electrocatalytic activities with their fundamental chemical structure of N doping and edge defect engineering. The metal-free product (NKCNPs-900) shows a high half-wave potential of 0.79 V (ORR). Furthermore, the assembled Zn-air batteries display excellent performance among carbon-based metal-free oxygen electrocatalysts, such as large peak power density up to 131.4 mW cm, energy density as high as 889.0 W h kg at 4.5 mA cm, and remarkable discharge-charge cycles up to 575 times. Preliminarily, the rechargeable nonaqueous Li-air batteries were also investigated. Therefore, our work provides a low-cost, metal-free, and high-performance bifunctional carbon-based electrocatalyst for metal-air batteries.

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