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Activation of molecular N2 and its catalytic ability to form NH3 using C17Si has been already reported. This current study reports the formation of exclusive polynitrogen clusters (N4 and N5) on the C17Si ring. The clusters are generated using N2 and N3 respectively. Physical and chemical property analyses of the clusters show that the N5 cluster exhibits greater stability than N4. The former is seen to experience reduced molecular strain compared to the latter owing to its co-planar geometry. The thermodynamic calculations of the systems further show that the formation of the N5 cluster is spontaneous compared to N4 on the C17Si ring.
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Activation of molecular nitrogen by silicon-substituted cyclo[18]carbon and its ability to produce the C17Si-(NH2)2 derivative, as the precursor of NH3, has been recently reported. This specific acquisition has piqued an interest to investigate the possibility of NH3 formation with further addition of H2 molecules in the gaseous reaction media. The current investigations reported in this article show that two moles of molecular H2 generate two molecules of NH3 and a C17Si-H2 byproduct from its precursor. The catalyst gets restored by an inâ situ reaction between some unreacted C17Si-N2 and the byproduct in the media. This reaction also produces the next C17Si-(NH)2 adduct, which restarts the catalytic cycle for NH3 production again.
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In this work, the significance of BlueP-Janus MoSSe heterostructures in LIBs is explored in detail by using density functional theory calculations. The Janus MoSSe possesses two different atomic layers, and hence two different heterostructures, BlueP-SMoSe and BlueP-SeMoS, are taken into account. The heterostructure formation energies are computed to check their stability. Besides, ab initio molecular dynamics simulations and phonon studies are done to check their thermal and dynamical stabilities, respectively. The adsorption and diffusion of Li at different surfaces of both the heterostructures are calculated. Our study reveals that the heterostructures show strong Li intercalation capability with ultrafast Li diffusion barrier energies. The electronic properties of the lithiated heterointerfaces are also explored. Both the heterostructures can hold a maximum of two layers of Li ions on each side of both BlueP and MoSSe to give a large storage capacity, signifying their extraordinary potential to be appropriate as an anode material for Li-ion batteries. Additionally, due to their strong mechanical strength, the 2D BlueP-Janus MoSSe heterostructures can withstand massive volume expansion during the lithiation-delithiation reaction, which is remarkably beneficial for manufacturing flexible anodes. Based on the above findings, the newly designed heterostructures are expected to open a new avenue for the next generation of electronic devices.
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Designing an efficient and cost-effective catalyst for ammonia borane (AB) dehydrogenation remains a persistent challenge in advancing a hydrogen-based economy. Transition metal complexes, known for their C-H bond activation capabilities, have emerged as promising candidates for AB dehydrogenation. In this study, we investigated two recently synthesized C-H activation catalysts, 1 (CoIV-dinitrate complex) and 2 (NiIV-nitrate complex), and demonstrated their efficacy for AB dehydrogenation. Using density functional theory calculations and a detailed analysis, we elucidated the AB dehydrogenation mechanism of these complexes. Our results revealed that both complexes 1 and 2 can efficiently dehydrogenate AB at room temperature, although the abstraction of molecular H2 from these complexes requires slightly elevated temperatures. We utilized H2 binding free energy calculations to identify potentially active sites and observed that complex 2 can release two equivalents of H2 at a temperature slightly higher than room temperature. Furthermore, we investigated AB dehydrogenation kinetics and thermodynamics in iron (Fe)-substituted systems, complexes 3 and 4. Our results showed that the strategic alteration of the central metal atom, replacing Ni in complex 2 with Fe in complex 4, resulted in enhanced kinetics and thermodynamics for AB dehydrogenation in the initial cycle. These results underscore the potential of high-valent first-row transition metal complexes for facilitating AB dehydrogenation at room temperature. Additionally, our study highlights the beneficial impact of incorporating iron into such mononuclear systems, enhancing their catalytic activity.
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A series of Mn(I) complexes Mn(L1 )(CO)3 Br, Mn(L2 )(CO)3 Br, Mn(L1 )(CO)3 (OAc) and Mn(L3 )(CO)3 Br [L1 =2-(5-tert-butyl-1H-pyrazol-3-yl)-1,8-naphthyridine, L2 =2-(5-tert-butyl-1H-pyrazol-3-yl)pyridine, L3 =2-(5-tert-butyl-1-methyl-1H-pyrazol-3-yl)-1,8-naphthyridine] were synthesized and fully characterized. The acid-base equilibrium between the pyrazole and the pyrazolato forms of Mn(L1 )(CO)3 Br was studied by 1 H NMR and UV-vis spectra. These complexes are screened as catalysts for acceptorless dehydrogenative coupling (ADC) of primary alcohols and aromatic diamines for the synthesis of benzimidazole and quinoline derivatives with the release of H2 and H2 O as byproducts. The protic complex Mn(L1 )(CO)3 Br shows the highest catalytic activity for the synthesis of 2-substituted benzimidazole derivatives with broad substrate scope, whereas a related complex [Mn(L3 )(CO)3 Br], which is devoid of the proton responsive ß-NH unit, shows significantly reduced catalytic efficiency validating the crucial role of the ß-NH functionality for the alcohol dehydrogenation reactions. Control experiments, kinetic and deuterated studies, and density functional theory (DFT) calculations reveal a synchronous hydride-proton transfer by the metal-ligand construct in the alcohol dehydrogenation step.
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Recent synthesis of sp-hybridized cyclo[18]carbon allotrope has attracted immense curiosity. Since then, a generous amount of theoretical studies concerning aromaticity, adsorption, and spectra of the molecule have been performed. However, very few stuides have been carried out concerning its reactivities and catalytic behaviour. In this article, a DFT-based inquisition has been reported regarding the reactivity of Si substituted cyclo[18]carbon molecule towards molecular N2 . Results show that the Si substituted derivative is effective in producing adducts with molecular nitrogen. Charge calculations and IRC trapping methods indicate that only the Si center of C17 Si and its (HOMO-1) level participate in N2 addition. The N-adduct so formed, is then found to spontaneously react with molecular H2 . The addition of two H2 molecules to the activated nitrogen molecule to give respective amine derivatives have also been studied. The successful generation of the precursor of NH3 by C17 Si lays a clear emphasis on its potentiality.
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Amoníaco , Nitrógeno , Amoníaco/química , Nitrógeno/química , Carbono , Silicio/químicaRESUMEN
Herein, we report a detailed periodic DFT investigation of Mn(II)-based [(Mn4 Cl)3 (BTT)8 ]3- (BTT3- =1,3,5-benzenetristetrazolate) metal-organic framework (MOF) to explore various hydrogen binding pockets, nature of MOF H2 interactions, magnetic coupling and, H2 uptake capacity. Earlier experiments found an uptake capacity of 6.9 wt % of H2, with the heat of adsorption estimated to be â¼10â kJ/mol, which is one among the highest for any MOFs reported. Our calculations unveil different binding sites with computed binding energy varying from -6 to -15â kJ/mol. The binding of H2 at the Mn2+ site is found to be the strongest (site I), with H2 found to bind Mn2+ ion in a η2 fashion with a distance of 2.27â Å and binding energy of -15.4â kJ/mol. The bonding analysis performed using NBO and AIM reveal a strong donation of σ (H2 ) to the dz 2 orbital of the Mn2+ ion responsible for such large binding energy. The other binding pockets, such as -Cl (site II) and BTT ligands (site III and IV) were found to be weaker, with the binding energy decreasing in the order I>II>III>IV. The average binding energy computed for these four sites put together is 9.6â kJ/mol, which is in excellent agreement with the experimental value of â¼10â kJ/mol. We have expanded our calculations to compute binding energy for multiple sites simultaneously, and in this model, the binding energy per site was found to decrease as we increased the number of H2 molecules suggesting electronic and steric factors controlling the overall uptake capacity. The calculated adsorption isotherm using the GCMC method reproduces the experimental observations. Further, the magnetic coupling computed for the unbound MOF reveals moderate ferromagnetic and strong antiferromagnetic coupling within the tetrameric {Mn4 } unit leading to a three-up-one-down spin configuration as the ground state. These were then coupled ferromagnetically to other tetrameric units in the MOF network. The magnetic coupling was found to alter only marginally upon gas binding, suggesting that both exchange interaction and the spin-states are unlikely to play a role in the H2 uptake. This is contrary to the O2 uptake studied lately, where strong dependence on exchange-coupling/spin state was witnessed, suggesting exchange-coupling/magnetic field dependent binding as a viable route for gas separation.
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The materials community is interested in discovering new two-dimensional (2D) crystals because of the potential for fascinating features. In this work, by employing a systematic first-principles DFT analysis and MD simulations, we investigated the potential applications of monolayer Mo borides containing flat and buckled boride rings named P6/mmm and R3Ìm MoB2 as anode materials of lithium-ion batteries. Our preliminary investigations show that the MoB2 monolayers possess significant structural, thermodynamic, mechanical, and dynamical stability. Due to their distinctive crystal structures, the Mo borides exhibit unique electronic properties, as expected. Additionally, we discovered that the highly negative Li adsorption energy achieved can aid in stabilizing the Li's adsorption on the surface of MoB2 rather than clustering, which ensured its suitability for LIB anode applications. The low computed Li-ion and Li-vacancy migration energy barrier provides robust charge/discharge performance even at a fully lithiated state, signifying their extraordinary possibility of being a suitable anode material for Li batteries. Both the monolayers can hold a maximum of two layers of Li ions on both sides to give a huge specific capacity of 912 mA h g-1, much higher than graphene and MoS2-based anodes. The computed in-plane stiffness constants demonstrate that the monolayer pristine and lithiated MoB2 satisfies Born's criteria, implying its mechanical flexibility. Additionally, its strong mechanical and thermal properties at the pristine and the lithiated state indicate that the 2D MoB2 can withstand massive volume expansion at a high temperature of 500 K during the lithiation/de-lithiation reaction and is remarkably beneficial for manufacturing flexible anodes. Based on the above findings, these two newly designed classes of monolayers of MoB2 are anticipated to open a new avenue for the upcoming generation of lithium-ion batteries.
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Sheehan's syndrome is a pituitary disease resulting from severe postpartum hemorrhage and can present with varying degrees of pituitary insufficiency. Although its incidence is decreasing in developed countries, it continues to be one of the most common causes of hypopituitarism in underdeveloped and developing countries. Here, we report a case of Sheehan's syndrome which was diagnosed following an episode of severe dengue infection, in a 38-year-old female.
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Dengue , Hipopituitarismo , Hemorragia Posparto , Embarazo , Femenino , Humanos , Adulto , Hipopituitarismo/complicaciones , Hipopituitarismo/diagnóstico , Dengue/complicaciones , Dengue/diagnósticoRESUMEN
PURPOSE: Recent reports have noted an emergence of unusual organisms in microflora of pilonidal sinus (PNS); this study was undertaken to identify the primary microbial flora associated with infected primary PNS over a period of 1 year. DESIGN: A prospective multiple case series. SUBJECTS AND SETTING: A case series of 20 patients with primary PNS in a tertiary care center in Varanasi, India, was studied. The study was conducted at the Department of Microbiology and General Surgery, Institute of Medical Sciences, Varanasi, over a period of 1 year (September 2016 to July 2017). METHODS: Purulent exudate (pus) samples were collected from 20 patients with primary PNS from the discharging sinuses by aseptic methods. Samples were assessed for aerobic and anaerobic flora by conventional culture and molecular methods. Antimicrobial susceptibility testing was done for bacterial isolates. Bacterial diversity was compared with the demographic and clinical profile of the sinuses by multiple correspondence analysis. RESULTS: Of the total cases, 11 (55%) had purulent discharge, among which all showed polymicrobial flora. The ratio of aerobic to anaerobic organisms was 1:2 (16/32). Escherichia coli (E. coli, 4, 36.36%) and Enterococcus faecalis (E. faecalis, 4, 36.36%) were commonly isolated. Bifidobacterium was the most frequent anaerobe. Detailed molecular analysis revealed the presence of Kocuria flava as an unusual pathogen. On statistical analysis, factors like male gender, increased body mass index, absence of hair in sinus, presence of features of hirsutism, and absence of Fusobacteria were closely associated with one another in these PNS cases. CONCLUSIONS: The case series revealed the predominance of anaerobes in primarily infected PNS cases. Bifidobacterium spp and unusual pathogens like K. flava were among the emerging pathogens in infected PNS. Use of better molecular diagnostic facilities in addition to the conventional methods might enhance the verified diversity of microorganisms in such cases.
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Seno Pilonidal , Humanos , Masculino , Escherichia coli , Estudios Prospectivos , IndiaRESUMEN
Invited for the cover of this issue are Sourav Pal, Gopalan Rajaraman and co-workers at the Indian Institute of Technology Bombay, the Bhabha Atomic Research Centre and the Indian Institute of Science Education and Research. The image depicts how a mixture of atmospheric gases such as CO2 , H2 , N2 and O2 can be selectively separated using a Cr metal-organic framework where spin state and spin coupling play a crucial role. Read the full text of the article at 10.1002/chem.202104526.
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The coordinatively unsaturated chromium(II)-based Cr3 [(Cr4 Cl)3 (BTT)8 ]2 (Cr-BTT; BTT3- =1,3,5-benzenetristetrazolate) metal-organic framework (MOF) has been shown to exhibit exceptional selectivity towards adsorption of O2 over N2 /H2 . Using periodic density functional theory (DFT) calculations, we attempted to decipher the origin of this puzzling selectivity. By computing and analyzing the magnetic exchange coupling, binding energies, the partial density of states (pDOS), and adsorption isotherms for the pristine and gas-bound MOFs [(Cr4 (X)4 Cl)3 (BTT)8 ]3- (X=O2 , N2 , and H2 ), we unequivocally established the role of spin states and spin coupling in controlling the gas selectivity. The computed geometries and gas adsorption isotherms are consistent with the earlier experiments. The binding of O2 to the MOF follows an electron-transfer mechanism resulting in a CrIII superoxo species (O2 .- ) with a very strong antiferromagnetic coupling between the two centers, whereas N2 /H2 are found to weakly interact with the metal center and hence only slightly perturb the associated coupling constants. Although the gas-bound and unbound MOFs have an S=0 ground state (GS), the nature of spin the configurations and the associated magnetic exchanges are dramatically different. The binding energy and the number of oxygen molecules that can favorably bind to the Cr center were found to vary with respect to the spin state, with a significant energy margin (47.6â kJ mol-1 ). This study offers a hitherto unknown strategy of using spin state/spin couplings to control gas adsorption selectivity in MOFs.
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Ru-Bis(pyridyl)borate complex (CAT) is an efficient catalyst for ammonia borane (AB) dehydrogenation. Although the mechanistic pathway of this catalyst has been theoretically investigated previously, the gap between the experimental findings and the computational results could not be bridged thus far. In our study, using density functional theory calculations, we elucidate the mechanism of AB dehydrogenation of CAT at a variable degree of ligand hydrogenation. Our results confirm that the acetonitrile ligands get reduced in the presence of AB and remain hydrogenated. Moreover, in line with experiments, we find that AB dehydrogenation on CAT proceeds via a concerted mechanism (with the free energy energetic span between 25.4 and 32.5 kcal/mol). We find that the ligand reduction alters the electronic structure and activity of CAT and the highest activity of the catalyst is expected at the fifth degree of hydrogenation of ligands with an energetic span of 25.4 kcal/mol. Additionally, the mechanism for the removal of molecular H2 from the catalysts also alters with the degree of ligand hydrogenation. Furthermore, our results show that optimal H2 binding free energy calculations can be used as a descriptor to identify the most active sites. Finally, this work demonstrates that ligand reduction improves the activity of the catalyst. These results highlight the importance of ligand hydrogenation in probing the activity and operating mechanism of the Ru-bis(pyridyl)borate complexes for AB dehydrogenation. Further, we identify a plausible dimer structure and rationalized experimental observation that the deactivation chemistry of this catalyst is different from the Shvo's catalyst.
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Molecular level understanding of liposome-gene interaction is immensely important for the research progress and technological advancement of gene delivery, which is highly significant due to a wide range of applications of gene therapy. The liposomal gene delivery method is one of the most promising techniques due to its efficacy to easily fuse with the cell membrane and its lower toxicity. In vivo gene delivery using liposomes is reported to be extremely successful. However, the success of gene delivery depends on various factors including the chemical nature of the structural unit of the liposome. To explore the regulative factor(s) for liposomal gene delivery, we systematically analyze the linker orientation effect on the gene delivery efficiency of liposomes through a density functional theory (DFT) study. Interestingly, it is observed that the liposome-gene interaction is not the regulating factor for successful gene delivery. The success depends on the gel to liquid melting temperature of the liposome.
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Liposomas , Terapia Genética , Liposomas/química , TemperaturaRESUMEN
Toll-like receptor 7 (TLR7) is activated in response to the binding of single-stranded RNA. Its over-activation has been implicated in several autoimmune disorders, and thus, it is an established therapeutic target in such circumstances. TLR7 small-molecule antagonists are not yet available for therapeutic use. We conducted a ligand-based drug design of new TLR7 antagonists through a concerted effort encompassing 2D-QSAR, 3D-QSAR, and pharmacophore modelling of 54 reported TLR7 antagonists. The developed 2D-QSAR model depicted an excellent correlation coefficient (R2training: 0.86 and R2test: 0.78) between the experimental and estimated activities. The ligand-based drug design approach utilizing the 3D-QSAR model (R2training: 0.95 and R2test: 0.84) demonstrated a significant contribution of electrostatic potential and steric fields towards the TLR7 antagonism. This consolidated approach, along with a pharmacophore model with high correlation (Rtraining: 0.94 and Rtest: 0.92), was used to design quinazoline-core-based hTLR7 antagonists. Subsequently, the newly designed molecules were subjected to molecular docking onto the previously proposed binding model and a molecular dynamics study for a better understanding of their binding pattern. The toxicity profiles and drug-likeness characteristics of the designed compounds were evaluated with in silico ADMET predictions. This ligand-based study contributes towards a better understanding of lead optimization and the future development of potent TLR7 antagonists.
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Relación Estructura-Actividad Cuantitativa , Receptor Toll-Like 7 , Diseño de Fármacos , Ligandos , Simulación del Acoplamiento Molecular , Simulación de Dinámica MolecularRESUMEN
A large surface-to-volume ratio is an essential feature of 2D materials used in many potential electronic applications. This work proposed that the haeckelite-structured phosphorus can be another promising alternative to the known phosphorus allotropes by DFT calculations. This allotrope can be considered a suitable anode material that may provide outstanding performance in LIBs and SIBs. Our simulations confirm that the haeckelite-structured P, composed of alternate square and octagonal rings, is thermally and mechanically stable. The phosphorus haeckelite exhibits a semiconductor with a bandgap of 2 eV and converts to a metallic phase after Li/Na adsorption, which is profoundly the basis for ideal performance of a battery. It provides a high specific capacity and a small OCV with a minimal volume expansion during lithiation/sodiation. The haeckelite-structured P exhibits much higher Li/Na adsorption properties with a small Li/Na migration barrier, which are highly essential in the charge-discharge performance of LIBs/SIBs. Based on the details mentioned above, our study would supply supportive guidelines to advance better opportunities to design and develop flexible Li/Na-ion batteries for future energy conversion and storage applications.
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In this paper, we present a formulation of highly correlated Fock-space multi-reference coupled-cluster (FSMRCC) methods, including approximate triples on top of the FSMRCC with singles and doubles, which correct the electron affinities by at least at third and up to the fourth order in perturbation. We discuss various partial fourth-order schemes, which are reliable and yet computationally more efficient than the full fourth-order triples scheme. The third-order scheme is called MRCCSD+T*(3). We present two approximate fourth-order schemes, MRCCSD+T*-a(4) and MRCCSD+T*(4). The results that are presented allow one to choose an appropriate fourth-order scheme, which is less expensive and right for the problem. All these schemes are based on the effective Hamiltonian scheme, and provide a direct calculation of the vertical electron affinities. We apply these schemes to a prototype Li2 molecule, using four different basis sets, as well as BeO and CH+. We have calculated the vertical electron affinities of Li2 at the geometry of the neutral Li2 molecule. We also present the vertical ionization potentials of the Li2 anion at the geometry of the anion ground state. We have also shown how to calculate adiabatic electron affinity, though in that case we lose the advantages of direct calculation. BeO has been examined in two basis sets. For CH+, four different basis sets have been used. We have presented the partial fourth-order schemes to the EA in all the basis sets. The results are analyzed to illustrate the importance of triples, as well as highlight computationally efficient partial fourth-order schemes. The choice of the basis set on the electron affinity calculation is also emphasized. Comparisons with available experimental and theoretical results are presented. The general fourth-order schemes, which are conceptually equivalent with the Fock-space multi-reference coupled-cluster singles, doubles, and triplets (MRCCSD+T) methods, based on bondonic formalism, are also presented here in a composed way, for quantum electronic affinity.
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Algoritmos , Electrones , Litio/química , Modelos Químicos , Teoría Cuántica , Fenómenos FísicosRESUMEN
Innovative van der Waals (vdW) heterostructures formed from various monolayers exhibit exceptional physical properties relevant to their corresponding individual layers. In addition, the strain engineering of 2D materials is significantly exciting because they have the potential to sustain much larger strain in comparison to their bulk counterparts. In this work, the influence of strain on a BlueP-MoS2 van der Waals heterostructure was studied in order to explore its performance in LIBs/SIBs by first-principles DFT calculations. To ascertain the influence of strain on the performance of the BlueP-MoS2 van der Waals heterostructure for electrodes in LIBs/SIBs, we gathered vertically aligned monolayers of MoS2 and BlueP with different amounts of strain and studied the Li/Na storage properties of the said material. The application of strain could effectively enhance the adsorption capability of both Li/Na at the surfaces/interface of the BlueP-MoS2 heterostructure in comparison to that of the pristine BlueP-MoS2 heterostructure along with improved storage capacity. On the other hand, the application of strain is robust to the high mobility of both Li/Na inside and outside surfaces of BlueP-MoS2 heterostructure which ensures the fast charge/discharge process and improved rate performance. The calculated electronic structure revealed that the applied strain converted the BlueP-MoS2 heterostructure from a semiconductor to a metal, indicating enhanced conductivity compared to that for the pristine BlueP-MoS2 heterostructure. All the above-mentioned findings suggest the high potential application of the BlueP-MoS2 vdW heterostructures for flexible nanoelectronic devices.
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The negative ion resonance states, which are electron-molecule metastable compound states, play the most important role in free-electron controlled molecular reactions and low-energy free-electron-induced DNA damage. Their electronic structure is often only poorly described but crucial to an understanding of their reaction dynamics. One of the most important challenges to current electronic structure theory is the computation of negative ion resonance states. As a major step forward, coupled-cluster theories, which are well-known for their ability to produce the best approximate bound state electronic eigen solutions, are upgraded to offer the most accurate and effective approximations for negative ion resonance states. The existing Fock-space coupled-cluster (FSCC) and the equation-of-motion coupled-cluster (EOM-CC) approaches that compute bound states are redesigned for the direct and simultaneous determination of both the kinetic energy of the free electron at which the electron-molecule compound states are resonantly formed and the corresponding autodetachment decay rate of the electron from the metastable compound state. This Feature Article reviews the computation of negative ion resonances using the FSCC approach and, in passing, provides the highlights of the equivalent EOM-CC approach.
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The electronic structure parameter (WM) of the nuclear magnetic quadrupole moment (MQM) interaction in numerous open-shell metal monofluorides (viz., MgF, CaF, SrF, BaF, RaF, and PbF) is computed in the fully relativistic coupled-cluster framework. The electron-correlation effects are found to be very important for the precise calculation of WM in the studied molecular systems. The molecular MQM interaction parameter scales nearly as Z2 in the alkaline earth metal monofluorides, where Z is the nuclear charge of metal. Our study identifies 223RaF as a good candidate for the experimental search of the nuclear MQM, which can help unravel the physics beyond the standard model in the hadron sector of matter.