Global Minimum Structure Research Articles

Rh19-: A high-spin super-octahedron cluster.

Probing atomic clusters with magic numbers is of supreme importance but challenging in cluster science. Pronounced stability of a metal cluster often arises from coincident geometric and electronic shell closures. However, transition metal clusters do not simply abide by this constraint. Here, we report the finding of a magic-number cluster Rh19- with prominent inertness in the sufficient gas-collision reactions. Photoelectron spectroscopy experiments and global-minimum structure search have determined the geometry of Rh19- to be a regular Oh‑[Rh@Rh12@Rh6]- with unusual high-spin electronic configuration. The distinct stability of such a strongly magnetic cluster Rh19- consisting of a nonmagnetic element is fully unveiled on the basis of its unique bonding nature and superatomic states. The 1-nanometer-sized Oh-Rh19- cluster corresponds to a fragment of the face-centered cubic lattice of bulk rhodium but with altered magnetism and electronic property. This cluster features exceptional electron-spin state isomers confirmed in photoelectron spectra and suggests potential applications in atomically precise manufacturing involving spintronics and quantum computing.

Insights into the growth law, electronic properties and spectra of Fenλ (n = 3–18; λ = 0, ±1) clusters

AbstractThe growth law, electronic properties and spectra of (n = 2–18; λ = 0, ±1) clusters have been examined by density functional theory (DFT) and an unbiased structure prediction method. Extensive geometry optimizations have been executed and show that the global minimum structures of clusters have a distinct growth law when n is 8–18. For n = 8–13 and 14–18, the iron atoms grow around a decahedral and icosahedral iron cluster core, respectively. Based on the present ground states, the calculated electronic parameters are in line with the experimental values. The thermal stability of charged iron cluster is higher than that of neutral iron cluster. The octahedral and icosahedral clusters are more stable than their neighbors. The former has low chemical activity and may be a superatom. The magnetic moment of Fe atom weakens in the cluster. The UV spectra, photoelectron spectra (PES) and infrared and Raman spectra of the clusters have been predicted and the global minimum structures of the clusters are determined by comparing the theoretical PES with the experimental results.

Growth pattern and electronic and magnetic properties of Cr-doped silver clusters.

Growth pattern and electronic and magnetic properties of Agn Cr (n = 1-16) clusters have been investigated via density functional theory (DFT) combined with CALYPSO structure search method. The optimized geometry shows that the growth of the global minimum structures of Agn Cr clusters have obvious rule. when n > 12, silver atoms grow around an icosahedron which is almost unchanged in each structure. Analyses of electronic properties indicate that the doped Cr atom can only enhance the stability of larger silver clusters. Optical absorption and photoelectron spectra of Agn Cr isomers have been predicted and can be used for their structural identification. The icosahedral Ag12 Cr cluster with large energy level gap can be seen as a superatom. The adsorption capacity of Cr atom in Agn Cr cluster to CO is much higher than that of free Cr atom. The intensity of IR and Ramam spectra can be dramatically enhanced when CO is absorbed on Agn Cr cluster that Cr atom is encapsulated by Ag atoms. Moreover, the red shift of IR and Raman spectra of CO adsorbed on these clusters is also very small compared to free CO. Magnetism calculations show that the magnetic moment of Agn Cr clusters decreases linearly from n = 6 to 12 and increases linearly from n = 12 to 16. The total magnetic moment of Agn Cr cluster is mainly localized on the Cr atom. The change of magnetic moment of Cr atom is related to the charge transfer between Cr and Ag atoms.

Rare Spin Avoided σ-σ Diradical Planar Tetracoordinate Boron Cluster: A Proto-Star for Planar Pentacoordination.

We report a global planar star-like cluster B3Li3 featuring three planar tetracoordinate boron centres with a rare spin avoided σ-σ diradical character. The cluster was found to be stable towards dissociation into different fragments. The spin density was found to be localized solely on the three boron atoms in the molecular plane. This spin avoided σ-σ diradical character leads to the extension of the coordination number to yield a neutral B3Li3H3 and a cationic B3Li3H3+ cluster with three planar pentacoordinate boron centres in their global minimum structures. The planar geometry of the aninonic B3Li3H3- cluster is slightly higher in energy. The planar global clusters were found to maintain planarity in their ligand protected benzene bound complexes, B3Li3(Bz)3, B3Li3H3(Bz)3 and B3Li3H3(Bz)3+ with high ligand dissociation energies offering candidature for experimental detection.

Interactions of arylhydroxylamines and alkylaldoximes with a rhodium porphyrin

Heme enzymes are involved in the binding and metabolism of hydroxylamine (RNHOH) and aldoxime (RCH=NOH) compounds (R = H, alkyl, aryl). We report the synthesis and X-ray crystal structure of a metalloporphyrin in complex with an arylhydroxylamine, namely that of (TPP)Rh(PhNHOH)(C6H4Cl) (TPP = tetraphenylpophryinato dianion). The crystal structure reveals, in addition to N-binding of PhNHOH to Rh, the presence of an intramolecular H-bond between the hydroxylamine –OH proton and a porphyrin N-atom. Results from density functional theory (DFT) calculations support the presence of this intramolecular H-bond in this global minimum structure, and a natural bond order (NBO) analysis reveals that this H-bond comprises a donor π N=C (porphyrin) to acceptor σ* O–H (hydroxylamine) interaction of 2.32 kcal/mol. While DFT calculations predict the presence of similar intramolecular H-bond interactions in the related aldoxime complexes (TPP)Rh(RCH=NOH)(C6H4Cl) in their global minima structures, the X-ray crystal structure obtained for the (TPP)Rh(CH3(CH2)2CH=NOH)(C6H4Cl) complex is consistent with the local (non-global) minima conformation that does not have this intramolecular H-bond interaction.

Molecular structure, electronic, topology and non-covalent interaction of 4-(Bis(2-chloroethyl)amino)-L-phenylalanine- Anti-blood cancer activity

In this study, it is attempted to scrutinize the global minimum energy structure of anti-blood cancer drug 4-(Bis(2-chloroethyl)amino)-L-phenylalanine (4B2CA-LPA) and functionalized density functional theory (DFT) calculations regarding their geometries, topological features of covalent, non-covalent interactions with employing Atoms in molecule (AIM) and Reduced density gradient (RDG) studies. As per the topological results, a new type of non-covalent attraction forces of hydrogen-hydrogen interaction was found in this molecule. Electrostatic potential variation as well as global reactive descriptor energy variations in the solvation phases was carried out by molecular electrostatic potential (MEP) and frontier molecular orbitals (FMOs) analysis. Moreover, the electronic excitations in liquids of 4B2CA-LPA were evaluated in UV-Vis absorptions. The local bonding electron transitions and optical properties of the compound were examined with natural bond orbital (NBO) studies. The 4B2CA-LPA molecule can serve as lead molecules for the growth of anti-blood cancer drugs. Molecular docking investigation has also been carried out to determine the ability of target molecules to bind with Hematopoietic inhibitors in blood cells.

Magic Numbers and Stabilities of Photoionized Water Clusters: Computational and Experimental Characterization of the Nanosolvated Hydronium Ion.

The stability and distributions of small water clusters generated in a supersonic beam expansion are interrogated by tunable vacuum ultraviolet (VUV) radiation generated at a synchrotron. Time-of-flight mass spectrometry reveals enhanced population of various protonated water clusters (H+(H2O)n) based upon ionization energy and photoionization distance from source, suggesting there are "magic" numbers below the traditional n = 21 that predominates in the literature. These intensity distributions suggest that VUV threshold photoionization (11.0-11.5 eV) of neutral water clusters close to the nozzle exit leads to a different nonequilibrium state compared to a skimmed molecular beam. This results in the appearance of a new magic number at 14. Metadynamics conformer searches coupled with modern density functional calculations are used to identify the global minimum energy structures of protonated water clusters between n = 2 and 21, as well as the manifold of low-lying metastable minima. New lowest energy structures are reported for the cases of n = 5, 6, 11, 12, 16, and 18, and special stability is identified by several measures. These theoretical results are in agreement with the experiments performed in this work in that n = 14 is shown to exhibit additional stability, based on the computed second-order stabilization energy relative to most cluster sizes, though not to the extent of the well-known n = 21 cluster. Other cluster sizes that show some additional energetic stability are n = 7, 9, 12, 17, and 19. To gain insight into the balance between ion-water and water-water interactions as a function of the cluster size, an analysis of the effective two-body interactions (which sum exactly to the total interaction energy) was performed. This analysis reveals a crossover as a function of cluster size between a water-hydronium-dominated regime for small clusters and a water-water-dominated regime for larger clusters around n = 17.

Generating candidates in global optimization algorithms using complementary energy landscapes.

Global optimization of atomistic structure relies on the generation of new candidate structures in order to drive the exploration of the potential energy surface (PES) in search of the global minimum energy structure. In this work, we discuss a type of structure generation, which locally optimizes structures in complementary energy (CE) landscapes. These landscapes are formulated temporarily during the searches as machine learned potentials (MLPs) using local atomistic environments sampled from collected data. The CE landscapes are deliberately incomplete MLPs that rather than mimicking every aspect of the true PES are sought to become much smoother, having only a few local minima. This means that local optimization in the CE landscapes may facilitate the identification of new funnels in the true PES. We discuss how to construct the CE landscapes and we test their influence on the global optimization of a reduced rutile SnO2(110)-(4 × 1) surface and an olivine (Mg2SiO4)4 cluster for which we report a new global minimum energy structure.

CONFPASS: Fast DFT Re-Optimizations of Structures from Conformation Searches.

CONFPASS (Conformer Prioritizations and Analysis for DFT re-optimizations) has been developed to extract dihedral angle descriptors from conformational searching outputs, perform clustering, and return a priority list for density functional theory (DFT) re-optimizations. Evaluations were conducted with DFT data of the conformers for 150 structurally diverse molecules, most of which are flexible. CONFPASS gives a confidence estimate that the global minimum structure has been found, and based on our dataset, we can have 90% confidence after optimizing half of the FF structures. Re-optimizing conformers in order of the FF energy often generates duplicate results; using CONFPASS, the duplication rate is reduced by a factor of 2 for the first 30% of the re-optimizations, which include the global minimum structure about 80% of the time.

Global Minimum Search and Bonding Analysis of Tl2 Hx and Tl3 Hy (x=0-6; y=0-5) Series.

A remarkable distinction between boron and carbon hydrides lies in their extremely different bonding patterns and chemical reactivity, resulting in diverse areas of application. Particularly, carbon, characterized by classical two-center - two-electron bonds, gives rise to organic chemistry. In contrast, boron forms numerous exotic and non-intuitive compounds collectively called non-classical structures. It is reasonable to anticipate that other elements of Group 13 exhibit their own unusual bonding patterns; however, our knowledge of the hydride chemistry for other elements in Group 13 is much more limited, especially for the heaviest stable element, thallium. In this work, we performed a conformational analysis of Tl2 Hx and Tl3 Hy (x=0-6, y=0-5) series via Coalescence Kick global minimum search algorithm, DFT, and ab initio quantum chemistry methods; we investigated the bonding pattern using the AdNDP algorithm, thermodynamic stability, and stability toward electron detachment. All found global minimum structures are classified as non-classical structures featuring at least one multi-center bond.

An investigating on the structures of Sc2Ge6− cluster and its CO adsorption by quantum chemical calculation

AbstractThe structures of the Sc2Ge6− cluster and its CO adsorption have been computational investigated. The density functional theory and couple cluster calculation are used to gether with the genetic algorithm in determine the minimum structures. This global minimum structure has the shape of a tetragonal bipyramid having two Sc atoms at two tops of pyramids binding with one edge of Ge‐Ge. The ground electronic state of the global minimum isomer is the 2B2 state in the C2v symmetry. The most stable isomer of Sc2Ge6− has been used to study the CO adsorption. The calculated results indicate that the Sc2Ge6− cluster has a good interaction with the CO molecule. The adsorption positions are around the Sc atom with two stable models include adsorbing the C atom and adsorbing both the C and O atoms of the CO molecule. Scandium doped germanium cluster can be used to produce materials that can treat CO gas by adsorption method.

<span>Calculations on the structures of MnB<sub>9</sub> clusters and its interaction with H<sub>2</sub></span>

The structures of the MnB9 cluster have been investigated by the theoretical calculations. The combination of the genetic algorithm and the density functional theory calculations (GA-DFT) find out seventeen minimum structures, including the local minimum structures and the global minimum structure. The MnB9 cluster can be formed by adding an Mn atom into the B9 cluster. There is also a strong interaction between the MnB9 cluster and the H2 molecule resulting in the expansion or dissociation of the H-H bond. This demonstrates the potential applicability of boron clusters doping manganese in the field of catalyst and adsorption.

Boron-Based Inverse Sandwich V2B7- Cluster: Double π/σ Aromaticity, Metal-Metal Bonding, and Chemical Analogy to Planar Hypercoordinate Molecular Wheels.

Inverse sandwich clusters composed of a monocyclic boron ring and two capping transition metal atoms are interesting alloy cluster systems, yet their chemical bonding nature has not been sufficiently elucidated to date. We report herein on the theoretical prediction of a new example of boron-based inverse sandwich alloy clusters, V2B7-, through computational global-minimum structure searches and quantum chemical calculations. This alloy cluster has a heptatomic boron ring as well as a perpendicular V2 dimer unit that penetrates through the ring. Chemical bonding analysis suggests that the inverse sandwich cluster is governed by globally delocalized 6π and 6σ frameworks, that is, double 6π/6σ aromaticity following the (4n + 2) Hückel rule. The skeleton B-B σ bonding in the cluster is shown not to be strictly Lewis-type two-center two-electron (2c-2e) σ bonds. Rather, these are quasi-Lewis-type, roof-like 4c-2e V-B2-V σ bonds, which amount to seven in total and cover the whole surface of inverse sandwich in a truly three-dimensional manner. Theoretical evidence is revealed for a 2c-2e Lewis σ single bond within the V2 dimer. Direct metal-metal bonding is scarce in inverse sandwich alloy clusters. The present inverse sandwich alloy cluster also offers a new type of electronic transmutation in physical chemistry, which helps establish an intriguing chemical analogy between inverse sandwich clusters and planar hypercoordinate molecular wheels.

Introducing a novel C50N10 azafullerene with chained nitrogen atoms on a buckyball pole: structure, stability, vibration, and electronic properties.

Fullerenes are of high significance due to their unique chemical properties and various applications in technology, particularly materials science, drug delivery, electronics, and nanoelectronics. In the recent years, many attempts have been focused to introduce new heteroatom-doped fullerenes having advanced chemical properties and tunable electronic traits, which make them a potential candidate for application in many branches of sciences. In this study, a novel C50N10 azafullerene with a fascinating structure of chained nitrogen atoms on a buckyball pole, with different electronic and optical properties compared to its other analogs, is introduced and trace of N-N substructures on the surface of C60 fullerene cage is investigated. For this molecule, four structural isomers including 3 structures with chain N atoms on a fullerene buckyball pole (NP isomers) and one isomer with separated N atoms (SN isomer) have been studied. All isomers have been studied with and without symmetry constraints, and the symmetry influence on the structure and stability of each isomer has been investigated. Although the studied NP structures have lower stability than the SN isomer, some reasons (such as their more all-carbon hexagonal rings, breaking some of their N-N bonds for partial opening of the cage and creating bigger rings in order to get rid of the unfavorable strain, as well as decreasing the N-N lone pair repulsions) lead to the acceptable stability of these structures with the bonded N atoms. The results of atomization energy and vibrational frequency calculations indicate that isomers with the bonded N atoms have acceptable stabilities and do not decompose into their constituent components. Investigation on the structural parameters demonstrates important roles of the number of all-carbon hexagonal rings, the number of N-N junction, and the molecule symmetry in the stability of the structures with the bonded N atoms. Study on the electronic and optical properties indicates that the target structures exhibit high electronic polarizability, relatively small HOMO/LUMO gap, high first- and second-order hyperpolarizability, and also large third-order nonlinear optical properties. All calculations have been performed using Gaussian G09 software using density functional theory (DFT) approach. Three-parameter Beck hybrid exchange functional (B3) hybridized with nonlocal correlation functional of Lee, Yang, and Parr (LYP) has been employed as the level of DFT calculations. All optimizations have been performed at double-zeta polarized (DZP) split valence 6-31G(d,p) and also at split valence TZP 6-311G(d,p) basis sets. The global minimum structures have been confirmed by frequency calculations at the same level of optimizations. The natural bond orbital (NBO) analyses, frontier orbital surfaces imaging, atomic charges, and charge transfer analyses have been achieved by GenNBO program package.

Structural, electronic, and spectral properties of AlnCuk (n = 1–16; k= 0, ±1) alloy clusters

The structural, electronic, and spectral properties of AlnCuk (n = 1–16; k = 0, ±1) clusters have been examined via ab initio calculations combined with the CALYPSO method. It is found that the Cu atom in the ground-state AlnCuk cluster is situated on the surface for n = 1–11 and prefers a central site for n = 12–16 (except for in Al15Cu, Al12Cu+, and Al16Cu+). The stability, chemical activity, ionization potential, and electron affinity of the AlnCuk clusters are closely linked to the cluster size, the number of valence electrons, the point group, and the spin state. Simultaneously, we simulated UV spectra, photoelectron spectra, and vibrational and Raman spectra of the AlnCuk clusters. The global minimum structure of the AlnCu− cluster is recognized by our comparing the simulated and measured photoelectron spectra.

Exploring the Structure and Bonding of Group 13 Homogeneous and Heterogeneous Hydrides with the X2H4 Stoichiometry: A Theoretical Investigation

We investigated the structure evolution of the Group 13 hydrides on the example of X2H4 (X = B, Al, Ga, In, Tl) and BAlH4, AlGaH4, GaInH4, and InTlH4 stoichiometries via density functional theory (DFT) and ab initio quantum chemistry methods performing Coalescence Kick (CK) global minimum search and AdNDP chemical bonding analysis. We found that all global minimum structures possess multicenter electron bonds. The difference between the structures of X2H4 stoichiometry for boron and aluminum is much more significant than that between other pairs of Al-Ga, Ga-In, and In-Tl. The evolution of Group 13 hydride structure involves the gradual prevalence of classical 2c-2e bonds over multicenter bonds for heavier elements. The found structural features of the heterogeneous hydrides are in total agreement with those of homogeneous hydrides and with the trends common for the periodic table that allows us to investigate the structural evolution of Group 13 hydrides more completely.

Theoretical study on the evolution of Pd catalysts and the effect on catalytic activity and selectivity during H2O2 direct synthesis

Pd catalysts show high activity and selectivity for hydrogen peroxide (H2O2) direct synthesis. The catalytic performance is found to be strongly dependent on the catalyst size, and metallic Pd catalysts can be partially oxidized during reaction. To determine the active center of H2O2 direct synthesis, the catalytic activity of Pd with different oxidation degree was investigated in this study by using density functional theory. Firstly, the global minimum structures of Pdn, (PdO)n, and (PdO0.5)n (n= 4, 12, and 19) were obtained using minimum hopping method. It is found that the oxidation can induce significant structural reconstruction, which enhances the Pd-O interaction. The reaction paths of H2O2 and H2O formation were obtained, and then the rate coefficients were calculated to study the reactivity and selectivity. Pd(111) surfaces with different O coverage were also considered. After oxidized, the larger Pd nanoclusters and Pd(111) surface show higher reaction activity and H2O2 selectivity, due to the weakened O2 adsorption strength, increased energy barriers of H2O2 and OOH dissociation, and 0.32 ML O/Pd(111) shows superior catalytic activity and H2O2 selectivity. The partially oxidized Pd sites have high activity and selectivity for H2O2 formation. This work provides an insight into the evolution of Pd catalysts and the effect on catalytic performance during H2O2 direct synthesis.

Advanced machine learning based global optimizations for Pt nanoclusters

Pt-nanoclusters have attracted attention due to their extensive use as catalysts in various sectors and their catalytic capabilities, instigating a theoretical investigation to correlate structure and property. On the other hand, it is challenging to find stable and reliable structures to support experimental results at the nanoscale due to their fluxional nature at ambient temperature. The major objective of this work is to test the capability of stable and reliable structure findings at the nanocluster region by Gaussian Process Regression (GPR) model potentials on-the-fly within the evolutionary framework using the Bayesian optimization approach. The entire algorithm is called Global Optimizations by GPR (GO-GPR) learning. In this regard, the GO-GPR algorithm examined the potential energy surfaces of bare Ptn-nanoclusters of sizes (n = 3–6, 7, 8, 10, 13). GO-GPR identified new low-lying isomers and global minimum structures are in correlation with earlier studies. In the case of Pt13 and Pt8 nano-clusters, the global minimum structure is close to the second lowest energy structure, implying that these clusters can have fluxional nature. In fact, a few experimental studies have shown that Pt8 and Pt13 are effective in catalyzing reactions.

Hollow polyhedral structures and properties of Ag2n-1Sn- (n = 2-11) clusters: A theoretical study.

The structures of Ag2n-1Sn- (n = 2-11) clusters are obtained by the combination of genetic algorithm (GA) and density functional theory (DFT). All the global minimum structures prefer hollow polyhedral structures, in which S-Ag-S element, triangular Ag3S3 and tetragonal Ag4S4 units present to stabilize the structures. The S atoms in the structures appear in μ3-S or μ4-S form. Adiabatic and vertical electron affinities of the clusters have been obtained, which reveals that they increases as cluster size. Stability analysis shows that Ag9S5- and Ag19S10- have special stability. The HOMO, LUMO orbitals of the clusters are obtained and the orbital components of them are calculated. The HOMO orbitals are mainly from the p orbitals of S atoms, whereas the s, p and d orbitals of Ag atoms contribute much bigger than the p orbitals of S atoms for LUMO orbitals. The orbital delocalization indexes (ODI) of the HOMOs and LUMOs are calculated, and the small ODIs of the HOMOs and LUMOs for n = 4-10 reveal that these orbitals are highly delocalized. By studying the projected density of states and molecular orbitals of Ag9S5- and Ag19S10- clusters, it is found that their molecular orbitals have superatomic properties. Superatomic properties play an important role in stabilizing clusters. This work used combined genetic algorithm and density functional theory (GA-DFT), and PBE0/Lanl2tz(Ag)/6-311G(d,p)(S) method to optimize the structures. Gaussian 16 program, Gauss view 6.0.16 program and Multiwfn 3.8 code are the softwares used.

Structural evolution, electronic and magnetic properties investigation of V3Sin− (n = 14–18) clusters based on photoelectron spectroscopy and density functional theory calculations

Silicon clusters doped with a transition metal (TM) atom have been intensively studied due to their novel properties and superior stability for possible usage as building blocks of future nanoelectronics. Besides the selection of the doped element, introducing the number of dopant atoms as another dimension adds versatility to tuning the cluster properties. However, there are few studies of silicon clusters doped with multiple TM atoms. Here, we present a study of V3Sin− (n = 14–18) by combining high-resolution photoelectron spectroscopy (PES) measurements with a search of their global minimum energy structures based on a homemade genetic algorithm coupled with density functional theory (DFT) for energy calculations. The simulated photoelectron spectra of the putative global minimum structures are in fair agreement with the experimental ones, which gives evidence for their authenticity as the ground-state structures. In these clusters the three V atoms always bond with each other and form an acute triangle, which can be seen as a nanoscale analogue of phase segregation in the bulk. For the size range n = 14–17, each of the ground-state structures has a silicon basket-like structure with the vanadium triangle inside, while V3Si18− has a baseball-mitt-like structure almost completely encapsulating the V3 triangle. The average binding energy of TMSin− (TM = V1, V2, V3) indicates that the more V atoms are doped the more stable the clusters are. Among these clusters, only V3Si14− have a total magnetic moment of 2 μB, making it a potential structural unit for magnetic storage devices. Mulliken population analysis and the electron spin density show that V atoms at different positions have different contributions to the total magnetic moments, and d electrons in V atoms contribute the most.