Strategies for improving the superconductivity of hydrides under high pressure.

The successful prediction and confirmation of unprecedentedly high-temperature superconductivity in compressed hydrogen-rich hydrides signify a remarkable advancement in the continuous quest for attaining room-temperature superconductivity. The recent studies have established a broad scope for developing binary and ternary hydrides and illustrated correlation between specific hydrogen motifs and high-Tcs under high pressures. The analysis of the microscopic mechanism of superconductivity in hydrides suggests that the high electronic density of states at the Fermi level (EF), the large phonon energy scale of the vibration modes and the resulting enhanced electron-phonon coupling are crucial contributors towards the high-Tcphonon-mediated superconductors. The aim of our efforts is to tackle forthcoming challenges associated with elevating theTcand reducing the stabilization pressures of hydrogen-based superconductors, and offer insights for the future discoveries of room-temperature superconductors. Our present Review offers an overview and analysis of the latest advancements in predicting and experimentally synthesizing various crystal structures, while also exploring strategies to enhance the superconductivity and reducing their stabilization pressures of hydrogen-rich hydrides.

High-temperature superconductivities and crucial factors influencing the stability of LaThH12 under moderate pressures.

The recent discovery of high-temperature superconductivity in compressed hydrides has reignited the long-standing quest for room-temperature superconductors. However, the synthesis of superconducting hydrides under moderate pressure and the identification of crucial factors that affect their stability remain challenges. Here, we predicted the ternary clathrate phases of LaThH12 with potential superconductivity under high pressures and specifically proposed a novel R3̄c-LaThH12 phase exhibiting a remarkable Tc of 54.95 K at only 30 GPa to address these confusions. Our first-principles studies show that the high-Tc value of Pm3̄m and Cmmm-LaThH12 phases was induced by the strong electron-phonon coupling driven by the synergy of the electron-phonon matrix element and phonon softening caused by Fermi surface nesting. Importantly, we demonstrate the dual effects of enhanced ionic bonding and expanded orbital hybridization between Th-6f and H-sp3 orbitals during depressurization are primary factors governing the dynamic stability of R3̄c-LaThH12 at low pressures. Our findings offer crucial insights into the underlying mechanisms governing low-pressure stability and provide guidance for experimental efforts aimed at realizing hydrogen-based superconductors with both low synthesis pressures and high-Tc.

Structural predictions of three medium-sized thiolate-protected gold nanoclusters Au44(SR)30, Au56(SR)32, and Au60(SR)34.

The knowledge of structural evolution among thiolate-protected gold nanoclusters is not only helpful for understanding their structure-property relationship but also provides scientific evidence to rule-guided structure predictions of gold nanoclusters. In this paper, three new atomic structures of medium-sized thiolate-protected gold nanoclusters, i.e. Au44(SR)30, Au56(SR)32, and Au60(SR)34, are predicted based on the grand unified model and ring model. Two structural evolution rules, i.e., Au44(SR)28 + [Au12(SR)4] → Au56(SR)32 + [Au12(SR)4] → Au68(SR)36 and Au44(SR)30 + [Au8(SR)2] → Au52(SR)32 + [Au8(SR)2] → Au60(SR)34 + [Au8(SR)2] → Au68(SR)36, are explored. The generic growth patterns underlying both sequences of nanoclusters can be viewed as sequential addition of four and three highly stable tetrahedral Au4 units on the cores, respectively. In addition, density functional theory calculations show that these three newly predicted gold nanoclusters have very close formation energies with their adjacent structures, large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps, and all-positive harmonic vibration frequencies, indicating their high stabilities.

Isomerism effects in relaxation dynamics of Au24(SR)16thiolate-protected gold nanoclusters.

Understanding the excited state behavior of isomeric structures of thiolate-protected gold nanoclusters is still a challenging task. In this paper, based on grand unified model and ring model for describing thiolate-protected gold nanoclusters, we have predicted four isomers of Au24(SR)16nanoclusters. Density functional theory calculations show that the total energy of one of the predicted isomers is 0.1 eV lower in energy than previously crystallized isomer. The nonradiative relaxation dynamics simulations of Au24(SH)16isomers are performed to reveal the effects of structural isomerism on relaxation process of the lowest energy states, in which that most of the low-excited states consist of core states. In addition, crystallized isomer possesses the shorter e-h recombination time, whereas the most stable isomer has the longer recombination time, which may be attributed to the synergistic effect of nonadiabatic coupling and decoherence time. Our results could provide practical guidance to predict new gold nanoclusters for future experimental synthesis, and stimulate the exploration of atomic structures of same sized gold nanoclusters for photovoltaic and optoelectronic devices.

[Au7(SR)7] Ring as a New Type of Protection Ligand in a New Atomic Structure of Au15(SR)13 Nanocluster.

We present a [Au7(SR)7] ring as a new type of protection ligand in a new atomic structure of Au15(SR)13 nanocluster for the first time based on the ring model developed to understand how interfacial interaction dictates the structures of protection motifs and gold cores in thiolate-protected gold nanoclusters. This new Au15(SR)13 model shows a tetrahedral Au4 core protected by one [Au7(SR)7] ring and two [Au2(SR)3] "staple" motifs. Density functional theory (DFT) calculations show that the newly predicted Au15(SR)13 (R = CH3/Ph) has a lower energy of 0.24/0.68 eV than previously proposed isomers. By comparing calculated optical absorption spectra (UV), circular dichroism (CD) spectra, and powder X-ray diffraction (XRD) patterns with related experimental spectra, the calculated CD spectra of the newly predicted Au15(SR)13 (R = CH3/Ph) cannot reproduce the experimental results, indicating that the newly predicted Au15(SR)13 is a new structure that needs to be confirmed by experiment. In addition, DFT calculations also show that the newly predicted Au15(SR)13 (R = CH3/Ph) exhibits a large HOMO-LUMO gap, suggesting its high chemical stability. The proposition of the [Au7(SR)7] ring as a protection ligand in the newly predicted Au15(SR)13 not only enriches the types of protection ligands in thiolate-protected gold nanoclusters but also further confirms the effectiveness and rationality of the ring model for understanding the interfacial interaction between the protection motifs and gold cores in thiolate-protected gold nanoclusters.

Unraveling the Atomic Structures of 10-Electron (10e) Thiolate-Protected Gold Nanoclusters: Three Au32(SR)22 Isomers, One Au28(SR)18, and One Au33(SR)23.

The atomic structures of 10-electron (10e) thiolate-protected gold nanoclusters have not received extensive attention both experimentally and theoretically. In this paper, five new atomic structures of 10e thiolate-protected gold nanoclusters, including three Au32(SR)22 isomers, one Au28(SR)18, and one Au33(SR)23, are theoretically predicted. Based on grand unified model (GUM), four Au17 cores with different morphologies can be obtained via three different packing modes of five tetrahedral Au4 units. Then, five complete structures of three Au32(SR)22 isomers, one Au28(SR)18, and one Au33(SR)23 isomers can be formed by adding the thiolate ligands to three Au17 cores based on the interfacial interaction between thiolate ligands and gold core in known gold nanoclusters. Density functional theory calculations show that the relative energies of three newly predicted Au32(SR)22 isomers are quite close to two previously reported isomers. In addition, five new 10e gold nanoclusters have large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps and all-positive harmonic vibration frequencies, indicating their high stabilities.

Ring Model for Understanding How Interfacial Interaction Dictates the Structures of Protection Motifs and Gold Cores in Thiolate-Protected Gold Nanoclusters.

Understanding the effect of interfacial interactions between the protection motifs and gold cores on the stabilities of thiolate-protected gold nanoclusters is still a challenging task. Based on analyses of 95 experimentally crystallized and theoretically predicted thiolate-protected gold nanoclusters, we present a ring model to offer a deeper insight into the interfacial interactions for this class of nanoclusters. In the ring model, all the gold nanoclusters can be generically viewed as a fusion or interlocking of several [Aum(SR)n] (m = 4-8, 10, and 12 and 0 ≤ n ≤ m) rings. Guided by the ring model and the grand unified model, a new Au42(SR)26 isomer is predicted, whose total energy is lower than those of two previously crystallized isomers. The ring model offers a mechanistic understanding of the interactions between the protection ligands and gold cores and practical guidance on predicting new gold nanoclusters for future experimental synthesis and confirmation.

Two-dimensional growth mode of thiolate-protected gold nanoclusters Au28+4n(SR)20+2n (n = 0-8): compared with their one-dimensional growth mode.

In this paper, six new atomic structures of thiolate-protected gold nanoclusters, i.e. Au32(SR)20, Au40(SR)26, Au48(SR)30, two Au56(SR)34, and Au60(SR)36, are predicted. Considering these six newly predicted structures and six previously predicted or crystallized Au28(SR)20, Au36(SR)24, Au44(SR)28, Au52(SR)32, and Au60(SR)36 altogether, the two-dimensional (2D) growth mode of Au28+4n(SR)20+2n (n = 0-8) nanoclusters is completely presented to compare with their one-dimensional (1D) growth mode. In Au28+4n(SR)20+2n (n = 0-8) nanoclusters with both 1D and 2D growth modes, the same number of gold-core atoms with different morphologies can be seen. Furthermore, the growth of the gold cores occurs via sequential fusion of one tetrahedral Au4 unit by sharing one gold atom. In addition, density functional theory calculations show that these six newly predicted gold nanoclusters following the 2D growth mode have relative energies very close to those of their isomeric structures following the 1D growth mode, large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps, and all-positive harmonic vibration frequencies, indicating their high stabilities. Therefore, the complete presentation of the 2D growth mode of Au28+4n(SR)20+2n (n = 0-8) is beneficial not only for a better understanding of the structural growth of gold nanoclusters, but also for a theoretical guidance on the prediction of new stable structures for experimental confirmation.