Valence Electron Configuration Research Articles

Samarium cation (Sm+) reactions with H2, D2, and HD: SmH+ bond energy and mechanistic insights from guided ion beam and theoretical studies.

Guided ion beam tandem mass spectrometry is used to study the reaction of the lanthanide samarium cation (Sm+) with H2 and its isotopologues (HD and D2) as a function of collision energy. Modeling the resulting energy dependent product ion cross sections from these endothermic reactions yields 2.03 ± 0.06 eV (two standard deviations) for the 0 K bond dissociation energy of SmH+. Quantum chemical calculations are performed to determine stabilities of the ground and low-energy states of SmH+ for comparison with the experimentally measured thermochemistry. The calculations generally overestimate the SmH+ bond energy, but a better agreement between experiment and theory is achieved after correcting for spin-orbit energy contributions, with coupled-cluster with single, double and perturbative triple excitations/complete basis set [CCSD(T)/CBS] results reproducing the experiment well. In the HD reaction, the SmH+ product is observed to be favored over the SmD+ by about a factor of three, indicating that the reaction proceeds via a direct mechanism with short-lived intermediates. This is consistent with quantum chemical calculations of relaxed potential energy surface scans of SmH2 +, which show that there is no strongly bound dihydride intermediate. The reactivity and hydride bond energy of Sm+, which has a valence electron configuration typical of most lanthanides, are compared with previous results for the lanthanide cations La+, Gd+, and Lu+, which exhibit configurations more closely related to the group 3 metal cations, Sc+ and Y+. Periodic trends across the lanthanide series and insights into the role of the electronic configurations on hydride bond strength and reactivity with H2 are discussed.

D0-d half-Heusler alloys: A potential class of advanced spintronic materials

The possibility of ferromagnetic half-metallicity in lithium-based half-Heusler alloys, such as MnPLi, has been theoretically explored before [Damewood et al., Phys. Rev. B 91, 064409 (2015)], although at optimized lattice constants such lithiated manganese pnictides are predicted to be ordinary ferromagnets and therefore not suitable for spintronic applications. In the following, however, it is shown by first principles density functional calculations that half-Heusler alloys formed by 3d transition metals and d0 alkali or alkaline-earth metals, which are defined by the valence electronic configuration ns1,2,(n−1)d0, can produce all kinds of half-metallic behavior at optimized lattice constants including the elusive Dirac half-metallicity that is theoretically predicted for the first time in a three-dimensional prototype MnPK. Together with the predicted magnetic and mechanical stability, this could pave the way for massless and dissipationless spintronics of the future. Among other technologically important features of the prototype Dirac half-metal MnPK, are the maximal moment d-shell ferromagnetism, high Fermi velocity of Dirac fermions that is comparable with that in graphene, and a wide half-metallic gap. Furthermore, by considering the prototype conventional half-metal VSbSr, the introduction of d0 metals is shown to substantially reduce the hull distance and produce true metastability in the otherwise instable chemical structure of zinc-blende transition metal pnictides–in this case zinc-blende VSb–without altering the ‘p-d exchange’ that is mainly responsible for their half-metallicity, thus bringing their realization and potential applications in spintronics a step closer to reality.

Enhanced localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel in high-concentration hydrochloric acid solutions at room temperature

The localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel (NC-304SS) produced by severe rolling technique, and its conventional polycrystalline 304 stainless steel (CC-304SS) counterpart, were investigated in high-concentration hydrochloric acid solutions at room temperature. NC-304SS can scarcely suffer from localized corrosion in 4 mol/L and 5 mol/L HCl solutions during 5-day immersion tests, and in 1–3mol/L HCl solutions during thirty-five-day immersion tests. The corrosion rate of NC-304SS was also less than that of CC-304SS during these immersion tests. The improved localized and uniform corrosion resistances of NC-304SS were explained in terms of the adsorption and chemical activity of Cl− on NC-304SS and CC-304SS characterized by X-ray photoelectron spectroscopy, and the valence electron configurations of NC-304SS and CC-304SS were characterized by ultra-violet photoelectron spectroscopy rather than conventional electrochemical results.

Spectroscopy and formation of lanthanum-hydrocarbon radicals formed by association and carbon-carbon bond cleavage of isoprene.

La atom reaction with isoprene is carried out in a laser-vaporization molecular beam source. The reaction yields an adduct as the major product and C-C cleaved and dehydrogenated species as the minor ones. La(C5H8), La(C2H2), and La(C3H4) are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of all three species exhibit a strong origin band and several weak vibronic bands corresponding to La-ligand stretch and ligand-based bend excitations. La(C5H8) is a five-membered metallacycle, whereas La(C2H2) and La(C3H4) are three-membered rings. All three metallacycles prefer a doublet ground state with a La 6s1-based valence electron configuration and a singlet ion. The five-membered metallacycle is formed through La addition and isoprene isomerization, whereas the two three-membered rings are produced by La addition and insertion, hydrogen migration, and carbon-carbon bond cleavage.

Synthesis and photoluminescence of doped Si3N4 nanowires with various valence electron configurations

In this work, Y-, Ce- and Tb-doped Si3N4 nanowires have been successfully synthesized by directly nitriding-doped nanocrystalline silicon powders obtained by cryomilling. The obtained single-crystalline α-Si3N4 nanowires are nearly 20–50 nm in diameter and up to several micrometers in length. The photoluminescence properties of doped Si3N4 nanowires have also been investigated. The Y-doped Si3N4 nanowires exhibit the main peak at 425 nm, Ce-doped Si3N4 nanowires show a narrow emission peak at 450 nm, and Tb-doped Si3N4 nanowires present a strong and sharp emission peak at 545 nm. Combining with our previous works on Al-, La- and Eu-doped Si3N4 nanowires, the effects of dopants with different valence electron configurations on the photoluminescence properties have been explored. The present study provides a guide to fabricate Si3N4-based nanomaterials for different photonic applications.

Dirac-like half-metallicity of [formula omitted] half-Heusler alloys

Notwithstanding the intuitive chemical bond view that atoms devoid of d electrons are unable to form d−d covalent bond, rigorous density functional band structure calculations indicate that half-Heusler alloys of 3d transition metals and d0 alkali or alkaline-earth metals defined by the valence electronic configuration ns1,2(n−1)d0, can produce all kinds of half-metallic behavior including the elusive Dirac-like half-metallicity that is reported in the prototype d0−d half-Heusler alloy CoKSb such that a sizable gap appears in the minority-spin band structure at the Fermi level, whereas in the majority-spin channel the conduction and the valence bands touch directly at the Γ point and the Fermi level. The linear dispersion of the conduction band and one of the valence bands in the majority-spin channel, indicates that the carriers have vanishingly small band-mass, very high mobilities, and are 100% spin-polarized. This finding is of immense interest for spintronic applications because the Dirac massless fermions–as in graphene–have remarkable properties that are now combined with 100% spin polarization in half-Heusler CoKSb.

Ab initio investigation of structure, spectrum, aromaticity and electronic properties of C10 carbon cluster

The predicted lower energy structures of neutral carbon cluster C10 are presented by using the particle swarm optimization method in combination with quantum chemistry calculation. Our results describe a wonderful diversity of C10 configuration with the DFT and MP2 methods. For linear and cyclic clusters, the energy of most stable monocyclic structure with D5h symmetry is lower by 1.38kcal/mol than the transition isomers with D10h symmetry at CCSD(T)/cc-pVTZ level, which is consistent with the previous theoretical results by others. All linear structures of C10 cluster have been certified as the metastable states at different calculation methods in this work. Simulated infrared spectra reveals that the extensive electron localization exists in the D10h configuration leading to the decreasing of the number of vibration modes compared with D5h configuration. The nucleus independent chemical shift (NICS) calculations indicate that planar C10 system is a stable aromatic compound and the position used to calculate the aromatic indices can be affected by the most shielding or deshielded location that we employed. The contribution of the delocalized electrons to the π-aromaticity is identical in C1a and C1b. By the adaptive natural density partitioning (AdNDP) and canonical molecular orbital (CMO) analysis, we know that the highly symmetric structures have more energy degenerate CMOs and 2 center-2 electron bond connection, and monocyclic C10 cluster is a globally doubly (σ- and π-) aromatic compound. Topological analysis and natural bond orbital (NBO) analysis show that there isn’t any electrostatic type of interactions in C10 structures, and much of negative natural valence electron configuration comes from high angular momentum orbitals. According to the electron configurations, the natural hybrid orbital is mainly composed of sp hybrid in the systems. It is worth mentioning that the competition of complicated many-body effects plays a significant role in stabilizing the distorted configuration of C10 cluster. We expect our work can provide more information for further experimental studies.

Mechanical characteristics of FeAl2O4 and AlFe2O4 spinel phases in coatings – A study combining experimental evaluation and first-principles calculations

FeAl2O4 and AlFe2O4 have similar spinel structures but different atomic arrangements, leading to different properties. In this study, mechanical properties and structures of the two spinel phases in composite coatings prepared by reactive plasma spraying of Fe2O3-Al composite powder were investigated by means of multi-mode atomic force microscopy, X-ray diffraction, and scanning electron microscopy. It was demonstrated that AlFe2O4 was stronger than FeAl2O4 with a higher electron work function (EWF). First-principles calculations were conducted to understand the difference in mechanical properties between the two phases. It was shown that FeAl2O4 and AlFe2O4 have “normal” and “inverse” spinel structures with different configurations of valence electrons: Fe2+tet(Al3+)2O4 and Fe3+tet(Fe2+Al3+)octO4. Compared to Fe2+tet(Al3+)2O4, Fe3+tet(Fe2+Al3+)octO4 has its O and Fe atoms in the octahedral sites forming covalent bonds, which increase the stability and strength of the crystal, corresponding to higher EWF and larger bulk, shear and Young's moduli.

Density Functional Study of Neutral and Charged Silver Clusters Agn with n = 2-22. Evolution of Properties and Structure.

Geometries and electronic properties of neutral Agn, cationic Agn+, and anionic Agn- silver clusters with n = 2-22 were investigated by density functional theory (DFT) with M06 functional. For neutral clusters, transition from planar to "empty cage" structure occurs at n = 7, "empty cage" to "cage with one Ag atom" at n = 18, and to "cage with two Ag atoms" at n = 22. For lowest-energy Agn clusters, Ag8 and Ag18 show lowest polarizability due to closed-shell valence electron configurations 1S2/1P6 and 1S2/1P6/1D10. High stability of Ag8 is manifested in small dissociation energies of Ag9 to Ag8 plus Ag1 and Ag10 cluster to Ag8 plus Ag2. Cluster Ag20 with configuration 1S2/1P6/1D10/2S2 is stable due to low dissociation energy of Ag21 to Ag1 and Ag22 to Ag2. Cationic clusters with even n namely Ag10+ (9 valence electrons), Ag16+ (15 valence electrons), and Ag22+ (21 valence electrons) dissociate to Ag1 and closed-shell Ag9+ (1S2/1P6), Ag15+ (1S2/1D10/2S2) and Ag21+ (1S2/1P6/1D10/2S2). For odd n, Ag11+ and Ag17+ dissociate to Ag2 and closed-shell Ag9+ and Ag15+. For anionic clusters Agn-, cohesion energy Ecoh and binding energy (BE) show maxima at n = 7 and n = 17 due to stable Ag7- and Ag17- clusters. Small Agn- clusters (n = 4-11) with even n (except n = 8) have lower dissociation energy for loss of Ag1 while those with odd n have lower dissociation energy for loss of Ag2. For n = 12-22, all clusters have lower dissociation energy for loss of Ag1.

Er3+ Photoluminescence in Er2@C82 and Er2C2@C82 Metallofullerenes Elucidated by Density Functional Theory.

Metallofullerenes with two erbium atoms encapsulated in IPR C82 cage isomers Cs-6 (I), C2v-9 (II), and C3v-8 (III) were investigated using density functional theory. The calculations suggest that erbium atoms assume a trivalent state with Er (4f11) valence electronic configuration in Er2@C82 and Er2C2@C82, where two electrons (6s2) per Er atom are transferred to the cage carrying four negative charges (C824-), while the third electron is promoted from the 4f to the 5d shell, becoming involved in covalent bonding to near atoms. Experimentally, Er3+-like emission from 4I13/2 to 4I15/2 was observed, and our calculations indicate that the Er-Er covalent metal bond in Er2@C82, and the Er-C/C2 covalent bonds in Er2C2@C82, can account for the observed photoluminescence despite the cage with C824-. Such existence is the reason that the C2 unit was found to be neutral on the basis of MEM-Rietveld X-ray measurements, although formally it should be described as C22-. Our prediction for isomer photoluminescence intensity agrees with the experimentally determined order (III > I > II), where the most pronounced activity of isomer III in Er2C2@C82 stems from its higher charge of formal Er3+ and its largest HOMO-LUMO gap.

Spectroscopy and formation of lanthanum-hydrocarbon radicals formed by C—C bond cleavage and coupling of propene

La reaction with propene is carried out in a laser-vaporization molecular beam source. Three La-hydrocarbon radicals are characterized by mass-analyzed threshold ionization (MATI) spectroscopy. One of these radicals is methylenelanthanum [La(CH2)] (Cs), a Schrock-type metal carbene. The other two are a five-membered 1-lanthanacyclopent-3-en [La(CH2CHCHCH2)] (Cs) and a tetrahedron-like trimethylenemethanelanthanum [La(C(CH2)3)] (C3v). Adiabatic ionization energies and metal-ligand stretching and hydrocarbon-based bending frequencies of these species are measured from the MATI spectra, preferred structures and electronic states are identified by comparing the experimental measurements and spectral simulations, and reaction pathways for the formation of the metal-hydrocarbon radicals are investigated with density functional theory calculations. All three radicals prefer doublet ground electronic states with La 6s1-based valence electron configurations, and singly charged cations favor singlet states generated by the removal of the La 6s1 electron. The metal-carbene radical is formed via multi-step carbon-carbon cleavage involving metallacyclization, β-hydrogen migration, and metal insertion. The metal-carbene radical formed in the primary reaction reacts with a second propene molecule to form the five-membered-ring and tetrahedron-like isomers through distinct carbon-carbon coupling paths.

Insights into the structures and electronic properties of Cun+1\u03bc and CunS\u03bc (n\u2009=\u20091\u201312; \u03bc\u2009=\u20090, \xb11) clusters

AbstarctThe stability and reactivity of clusters are closely related to their valence electronic configuration. Doping is a most efficient method to modify the electronic configuration and properties of a cluster. Considering that Cu and S posses one and six valence electrons, respectively, the S doped Cu clusters with even number of valence electrons are expected to be more stable than those with odd number of electrons. By using the swarm intelligence based CALYPSO method on crystal structural prediction, we have explored the structures of neutral and charged Cun+1 and CunS (n = 1–12) clusters. The electronic properties of the lowest energy structures have been investigated systemically by first-principles calculations with density functional theory. The results showed that the clusters with a valence count of 2, 8 and 12 appear to be magic numbers with enhanced stability. In addition, several geometry-related-properties have been discussed and compared with those results available in the literature.

Threshold Ionization and Spin-Orbit Coupling of Ceracyclopropene Formed by Ethylene Dehydrogenation.

A Ce atom reaction with ethylene was carried out in a laser-vaporization metal cluster beam source. Ce(C2H2) formed by hydrogen elimination from ethylene was investigated by mass-analyzed threshold ionization (MATI) spectroscopy, isotopic substitutions, and relativistic quantum chemical computations. The theoretical calculations include a scalar relativistic correction, dynamic electron correlation, and spin-orbit coupling. The MATI spectrum exhibits two nearly identical band systems separated by 128 cm(-1). The separation is not affected by deuteration. The two-band systems are attributed to spin-orbit splitting and the vibrational bands to the symmetric metal-ligand stretching and in-plane carbon-hydrogen bending excitations. The spin-orbit splitting arises from interactions of a pair of nearly degenerate triplets and a pair of nearly degenerate singlets. The organolanthanide complex is a metallacyclopropene in C2v symmetry. The low-energy valence electron configurations of the neutral and ion species are Ce 4f(1)6s(1) and Ce 4f(1), respectively. The remaining two electrons that are associated with the isolated Ce atom or ion are spin paired in a molecular orbital that is a bonding combination between a 5d Ce orbital and a π* antibonding orbital of acetylene.

The nature of structure and bonding between transition metal and mixed Si-Ge tetramers: A 20-electron superatom system.

A novel superatom species with 20-electron system, Six Gey M(+) (x + y = 4; M = Nb, Ta), was properly proposed. The trigonal bipyramid structures for the studied systems were identified as the putative global minimum by means of the density functional theory calculations. The high chemical stability can be explained by the strong p-d hybridization between transition metal and mixed Si-Ge tetramers, and closed-shell valence electron configuration [1S(2) 1P(6) 2S(2) 1D(10) ]. Meanwhile, the chemical bondings between metal atom and the tetramers can be recognized by three localized two-center two-electron (2c-2e) and delocalized 3c-2e σ-bonds. For all the doped structures studied here, it was found that the π- and σ-electrons satisfy the 2(N + 1)(2) counting rule, and thus these clusters possess spherically double (π and σ) aromaticity, which is also confirmed by the negative nucleus-independent chemical shifts values. Consequently, all the calculated results provide a further understanding for structural stabilities and electronic properties of transition metal-doped semiconductor clusters. © 2016 Wiley Periodicals, Inc.

Geometric, electronic and magnetic properties of Aun, Aun−1Pt and Aun−2Pt2 (n = 2–9) clusters: A first-principles study

We use inverse design of materials by multi-objective differential evolution (IM2ODE) method to globally search the most stable configurations of Aun,Aun-1Pt,Aun-2Pt2 (n=2–9) clusters. Combining with first-principles calculations, based on the density functional theory (DFT), we find that all of the ground state structures of clusters prefer to keep low spin multiplicity and form planar structures. Pt atom tends to occupy the most highly coordinated position. Especially Au6Pt and Au4Pt2 clusters exhibit highly relative stability and have a closed electronic shell based on the spherial jellium model, so we conclude that Au6Pt and Au4Pt2 should be magic number clusters. Mulliken occupation analysis of Pt and Au atoms indicate that a competition exits between electronegativity of atoms and valence electron configuration of atoms in small AunPtm clusters.

Quantum-chemical study of ytterbium fluorides and of complex F2YbF2CeF2

The structural parameters of the (2Σ+//C∞v )-YbF, (1A1//C2v )-YbF2, (2A 2 ′ //D3h )-YbF3, (1Ag//D2h )-YbF2Yb, (1Ag//C2h )-FYbF2YbF, (1A1//C2v )-FYbF2YbF, (1A1//C2v )-YbF2YbF2, (3B3u //D2h )-F2YbF2YbF2, (2A′//C s )-FYbF2YbF2, and (3B2//С2v )-F2YbF2CeF2 molecules have been determined. Disproportionation of ytterbium monofluoride (2YbF → YbF2 + Yb + 0.46 eV) is less exothermic than dimerization (2YbF → YbF2Yb + 2.10 eV). The bond energy of the ytterbium difluoride molecules in the trans dimer (2.93 eV) exceeds those in the cis dimer (2.86 eV) and the coaxial dimer (1.66 eV). Ytterbium trifluoride dimerizes exothermically (2.95 eV) without spin pairing. The dipole and quadrupole moments of the molecules as well as the charges and spin populations of the atoms and the valence electron configurations of the lanthanides have been calculated.

Density functional theory calculations of hydrogen dissociative adsorption on platinum-involved alloy surfaces

Density functional theory calculations of the H2 molecule over the Pt(111), Pt4Pd5(111), Pt3Ir6(111), and Pt8Ru1(111) surfaces were carried out to derive key properties involving interactions and electronic state of each atom. From the calculations, H2 dissociative adsorption shows the lowest barrier in case of the Pt3Ir6(111) surface. Pt4Pd5(111) and Pt8Ru1(111) surfaces show a small energy barrier, while the Cu(111) surface is the highest energy barrier. The difference in the reactivity of H2 molecule with the surface is pointed out by the differences in the valence electron configuration of approaching hydrogen which is also verified from the density of state curve. The electronic structure plots illustrate the substituted atoms can interact with molecular H2 projected on the surface d-orbital.

In-silico bonding schemes to encode chemical bonds involving sharing of electrons in molecular structures

Encoding of covalent and coordinate covalent bonds in molecular structures using ground state valence electronic configuration is achieved. The bonding due to electron sharing in the molecular structures is described with five fundamental bonding categories viz. uPair–uPair, lPair–uPair, uPair–lPair, vPair–lPair, and lPair–lPair. The involvement of lone pair electrons and the vacant electron orbitals in chemical bonding are explained with bonding schemes namely “target vacant promotion”, “source vacant promotion”, “target pairing promotion”, “source pairing promotion”, “source cation promotion”, “source pairing double bond”, “target vacant occupation”, and “double pairing promotion” schemes. The bonding schemes are verified with a chemical structure editor. The bonding in the structures like ylides, PCl5, SF6, IF7, N-Oxides, BF4−, AlCl4− etc. are explained and encoded unambiguously. The encoding of bonding in the structures of various organic compounds, transition metals compounds, coordination complexes and metal carbonyls is accomplished.

Effect of W content in solid solution on properties and microstructure of (Ti,W)C-Ni3Al cermets

(Ti1-xWx)C solid solutions (x = 0.05, 0.15, 0.25, 0.35) were synthesized by carbothermal reduction and then were used as hard phases to prepare (Ti,W)C-Ni3Al cermets by vacuum sintering. (Ti,W)C-Ni3Al cermets showed weak core-rim structure carbide particles embedded in Ni3Al binder. As W content in (Ti,W)C increased, core-rim structure of carbide particles got weaker and the contrast of particles lowered down in SEM-BSE morphologies. Furthermore, the densification of cermets was promoted with W content in solid solution increasing, meanwhile TRS and toughness of cermets were improved obviously. In this paper, the wettability of molten metal on different group transition metal carbides was discussed in detail based on valence-electron configurations (VECs) of carbides.

The electronic and magnetic properties of anion doped (C, N, S) GaFeO3; an ab initio DFT study

In this study we present ab initio DFT calculations performed on stoichiometric and anion doped GaFeO3 substituting O by a C, N and S atom, respectively. Stoichiometric GaFeO3 has an antiferromagnetic (AFM) ground state. The Fe atoms of the sublattices Fe1 and Fe2 couple antiferromagnetically via the O atoms through the superexchange mechanism. Replacing the superexchange mediating O atom with p-elements of a different valence electron configuration changes the underlying magnetic exchange mechanism and influence the ground state properties. This may be used for tuning properties interesting for technical applications. Four different doping configurations were examined revealing a cell site dependent influence on the magnetic properties. Carbon, for example, changes the AFM coupling present in the Fe1–O–Fe2 configuration into a ferrimagnetic exchange for the Fe1–C–Fe2 bond. Depending on the respective cell site C substitution introduces a ferrimagnetic or AFM ground state. Nitrogen alters the ground state magnetic moment as well and sulfur introduces large structural distortions affecting the band gap and the overall AFM coupling inside the doped GaFeO3 simulation cell. We give a detailed discussion on the respective magnetic exchange mechanisms and electronic properties with regard to applications as photocatalysis and use the predictive power of ab initio DFT simulations that may trigger future experiments in the very promising field of tunable multifunctional devices.