A Nonstochastic Optimization Algorithm for Neural-Network Quantum States.

Neural-network quantum states (NQS) employ artificial neural networks to encode many-body wave functions in a second quantization through variational Monte Carlo (VMC). They have recently been applied to accurately describe electronic wave functions of molecules and have shown the challenges in efficiency compared with traditional quantum chemistry methods. Here, we introduce a general nonstochastic optimization algorithm for NQS in chemical systems, which deterministically generates a selected set of important configurations simultaneously with energy evaluation of NQS. This method bypasses the need for Markov-chain Monte Carlo within the VMC framework, thereby accelerating the entire optimization process. Furthermore, this newly developed nonstochastic optimization algorithm for NQS offers comparable or superior accuracy compared to its stochastic counterpart and ensures more stable convergence. The application of this model to test molecules exhibiting strong electron correlations provides further insight into the performance of NQS in chemical systems and opens avenues for future enhancements.

Circuit-Depth Reduction of Unitary-Coupled-Cluster Ansatz by Energy Sorting.

Quantum computation represents a revolutionary approach to solving problems in quantum chemistry. However, due to the limited quantum resources in the current noisy intermediate-scale quantum (NISQ) devices, quantum algorithms for large chemical systems remain a major task. In this work, we demonstrate that the circuit depth of the unitary coupled cluster (UCC) and UCC-based ansatzes in the algorithm of the variational quantum eigensolver can be significantly reduced by an energy-sorting strategy. Specifically, subsets of excitation operators are first prescreened from the operator pool according to its contribution to the total energy. The quantum circuit ansatz is then iteratively constructed until convergence of the final energy to a typical accuracy. For demonstration, this method has been successfully applied to molecular and periodic systems. Particularly, a reduction of 50%-98% in the number of operators is observed while retaining the accuracy of the original UCCSD operator pools. This method can be straightforwardly extended to general parametric variational ansatzes.

Polyvalent s-block elements: A missing link challenges the periodic law of chemistry for the heavy elements.

The Periodic Law of Chemistry is one of the great discoveries in cultural history. Elements behaving chemically similar are empirically merged in groups G of a Periodic Table, each element with G valence electrons per neutral atom, and with upper limit G for the oxidation and valence numbers. Here, we report that among the usually mono- or di-valent s-block elements (G = 1 or 2), the heaviest members (87Fr, 88Ra, 119E, and 120E) with atomic numbers Z = 87, 88, 119, 120 form unusual 5- or 6-valent compounds at ambient conditions. Together with well-reported basic changes of valence at the end of the 6d-series, in the whole 7p-series, and for 5g6f-elements, it indicates that at the bottom of common Periodic Tables, the classic Periodic Law is not as straightforward as commonly expected. Specifically, we predict the feasible experimental synthesis of polyvalent [RaL-n] (n = 4, 6) compounds.

Toward practical quantum embedding simulation of realistic chemical systems on near-term quantum computers.

Quantum computing has recently exhibited great potential in predicting chemical properties for various applications in drug discovery, material design, and catalyst optimization. Progress has been made in simulating small molecules, such as LiH and hydrogen chains of up to 12 qubits, by using quantum algorithms such as variational quantum eigensolver (VQE). Yet, originating from the limitations of the size and the fidelity of near-term quantum hardware, the accurate simulation of large realistic molecules remains a challenge. Here, integrating an adaptive energy sorting strategy and a classical computational method-the density matrix embedding theory, which respectively reduces the circuit depth and the problem size, we present a means to circumvent the limitations and demonstrate the potential of near-term quantum computers toward solving real chemical problems. We numerically test the method for the hydrogenation reaction of C6H8 and the equilibrium geometry of the C18 molecule, using basis sets up to cc-pVDZ (at most 144 qubits). The simulation results show accuracies comparable to those of advanced quantum chemistry methods such as coupled-cluster or even full configuration interaction, while the number of qubits required is reduced by an order of magnitude (from 144 qubits to 16 qubits for the C18 molecule) compared to conventional VQE. Our work implies the possibility of solving industrial chemical problems on near-term quantum devices.

Theoretical prediction of a graphene-like 2D uranyl material with p-orbital antiferromagnetism.

Versatile graphene-like two-dimensional materials with s-, p- and d-block elements have aroused significant interest because of their extensive applications while there is a lack of such materials with f-block elements. Herein we report a unique one composed of the f-block element moiety of uranyl (UO2 2+) through a global-minimum structure search. Its geometry is found to be similar to that of graphene with a honeycomb-like hexagonal unit composed of six uranyl ligands, where each uranyl is bridged by two superoxido groups and a pair of hydroxyl ligands. All the uranium and bridging oxygen atoms form an extended planar 2D structure, which shows thermodynamic, kinetic and thermal stabilities due to σ/π bonding as well as electrostatic interactions between ligands. Each superoxido ligand has one unpaired (2pπ*)1 electron and is antiferromagnetically coupled through uranyl bridges with 2pπ*-5f δ -2pπ* superexchange interactions, forming a rare type of one-dimensional Heisenberg chain with p-orbital antiferromagnetism, which might become valuable for application in antiferromagnetic spintronics.

Electronic Structure and Spectroscopic Properties of Group-7 Tri-Oxo-Halides MO3X (M = Mn-Bh, X = F-Ts).

The 24 trioxide halide molecules MO3X of the manganese group (M = Mn-Bh; X = F-Ts), which are iso-valence-electronic with the famous MnO4- ion, have been quantum-chemically investigated by quasi-relativistic density-functional and ab initio correlated approaches. Geometric and electronic structures, valence and oxidation numbers, vibrational and electronic spectral properties, energetic stabilities of the monomers in the gas phase, and the decay mode of MnO3F have been investigated. The light Mn-3d species are most strongly electron-correlated, indicating that the concept of a closed-shell Lewis-type single-configurational structure [Mn+7(d0) O-2(p6)3 F-(p6)] reaches its limits. The concept of real-valued spin orbitals φ(r)·α and φ(r)·ß breaks down for the heavy Bh-6d, At-6p and Ts-7p elements because of the dominating spin-orbit coupling. The vigorous decomposition of MnO3F at ambient conditions starts by the autocatalyzed release of n O2 and the formation of MnmO3m-2nFm clusters, triggered by the electron-depleted "oxylic" character of the oxide ligands in MnO3X.

2-Butene Tetraanion Bridged Dinuclear Samarium(III) Complexes via Sm(II)-Mediated Reduction of Electron-Rich Olefins.

While reduction reactions are ubiquitous in chemistry, it is very challenging to further reduce electron-rich compounds, especially the anionic ones. In this work, the reduction of 1,3-butadienyl dianion, the anionic conjugated olefin, has been realized by divalent rare-earth metal compounds (SmI2), resulting in the formation of novel 2-butene tetraanion bridged disamarium(III) complexes. Density functional theory (DFT) analyses reveal two features: (i) the single electron transfer (SET) from 4f atomic orbitals (AOs) of each Sm center to the antibonding π*-orbitals of 1,3-butadienyl dianion is feasible and the new HOMO formed by the bonding interaction between Sm 5d orbitals (AOs) and the π*-orbitals of 1,3-butadienyl dianion can accept favorably 2e- from 4f AOs of Sm(II); (ii) the 2-butene tetraanionic ligand serves as a unique 10e- donating system, in which 4e- act as two σ-donation bonding interactions while the rest 6e- as three π-donation bonding interactions. The disamarium(III) complexes represent a unique class of the bridged bis-alkylidene rare-earth organometallic complexes. The ligand-based reductive reactivity of 2-butene tetraanion bridged disamarium(III) complexes demonstrates that 2-butene tetraanionic ligand serves as a 3e- reductant toward cyclooctatetraene (COT) to provide doubly COT-supported disamarabutadiene complexes. The reaction of the disamarium(III) complexes with Cp*Li produces the doubly Cp*-coordinated Sm(III) complexes via salt metathesis. In addition, the reaction with Mo(CO)6 affords the oxycyclopentadienyl dinuclear complex via CO insertion.

Tuning radical interactions in trisradical tricationic complexes by varying host-cavity sizes.

Although host-guest pairing interactions between bisradical dicationic cyclobis(paraquat-p-phenylene) (BB2(˙+) ) and the bipyridinium radical cation (BIPY˙+ ) have been studied extensively, host molecules other than BB2(˙+) are few and far between. Herein, four bisradical dicationic cyclophanes with tunable cavity sizes are investigated as new bisradical dicationic hosts for accommodating the methyl viologen radical cation (MV˙+ ) to form trisradical tricationic complexes. The structure-property relationships between cavity sizes and binding affinities have been established by comprehensive solution and solid-state characterizations as well as DFT calculations. The association constants of the four new trisradical tricationic complexes are found to range between 7400 and 170 000 M-1, with the strongest one being 4.3 times higher than that for [MV⊂BB]3(˙+) . The facile accessibility and tunable stability of these new trisradical tricationic complexes make them attractive redox-controlled recognition motifs for further use in supramolecular chemistry and mechanostereochemistry.

Understanding Periodic and Non-periodic Chemistry in Periodic Tables.

The chemical elements are the "conserved principles" or "kernels" of chemistry that are retained when substances are altered. Comprehensive overviews of the chemistry of the elements and their compounds are needed in chemical science. To this end, a graphical display of the chemical properties of the elements, in the form of a Periodic Table, is the helpful tool. Such tables have been designed with the aim of either classifying real chemical substances or emphasizing formal and aesthetic concepts. Simplified, artistic, or economic tables are relevant to educational and cultural fields, while practicing chemists profit more from "chemical tables of chemical elements." Such tables should incorporate four aspects: (i) typical valence electron configurations of bonded atoms in chemical compounds (instead of the common but chemically atypical ground states of free atoms in physical vacuum); (ii) at least three basic chemical properties (valence number, size, and energy of the valence shells), their joint variation across the elements showing principal and secondary periodicity; (iii) elements in which the (sp)8, (d)10, and (f)14 valence shells become closed and inert under ambient chemical conditions, thereby determining the "fix-points" of chemical periodicity; (iv) peculiar elements at the top and at the bottom of the Periodic Table. While it is essential that Periodic Tables display important trends in element chemistry we need to keep our eyes open for unexpected chemical behavior in ambient, near ambient, or unusual conditions. The combination of experimental data and theoretical insight supports a more nuanced understanding of complex periodic trends and non-periodic phenomena.