Electronic Structures of Niobium Carbides: NbCn (n = 3−8)

Investigation of Structures, Stabilities, and Electronic and Magnetic Properties of Niobium Carbon Clusters Nb7Cn (n = 1-7)

The geometrical structures, relative stabilities, and electronic and magnetic properties of niobium carbon clusters, Nb7Cn (n = 1-7), are investigated in this study. Density functional theory (DFT) calculations, coupled with the Saunders Kick global search, are conducted to explore the structural properties of Nb7Cn (n = 1-7). The results regarding the average binding energy, second-order difference energy, dissociation energy, HOMO-LUMO gap, and chemical hardness highlight the robust stability of Nb7C3. Analysis of the density of states suggests that the molecular orbitals of Nb7Cn primarily consist of orbitals from the transition metal Nb, with minimal involvement of C atoms. Spin density and natural population analysis reveal that the total magnetic moment of Nb7Cn predominantly resides on the Nb atoms. The contribution of Nb atoms to the total magnetic moment stems mainly from the 4d orbital, followed by the 5p, 5s, and 6s orbitals.

Ground and Low-Lying Excited States of NbC3-/0 Clusters: Assignment of the Anion Photoelectron Spectra from Multiconfigurational Calculations

The BP86 DFT, CCSD(T), and CASPT2 methods were employed to study the low-lying states of NbC₃^-/0 clusters. The anionic and neutral ground states were determined to be the ¹A₁ and 1²A₁ of the cyclic-NbC₃^-/0 isomers. All bands in the photoelectron spectra of the NbC₃^- cluster were interpreted based on electron detachment processes from the ¹A₁ of the cyclic-NbC₃^- isomer. The X, A, B, and C bands in the spectra are, respectively, ascribed to the transitions from ¹A₁ to the 1²A₁, ²B₁, 2²A₁, and ²B₂ states. The wave function of the initial ¹A₁ anionic state exhibits a pronounced multireference character that plays to some extent a role in the ¹A₁ → 1²A₁ and the ¹A₁ → 2²A₁ ionizations. Only the ¹A₁ → ²B₂ transition appears as a clear one-electron detachment process. The Franck-Condon factor simulations for the ¹A₁ → 1²A₁ and ¹A₁ → ²B₁ transitions are consistent with the observed vibrational progressions of the X and A bands in the spectra.

First spectroscopic observation of gold(i) butadiynylide: Photodetachment velocity map imaging of the AuC4H anion

The velocity map imaging technique was used in the investigation of gold(i) butadiynylide, AuC4H(-), with images recorded at two excitation wavelengths. The resultant photodetachment spectra show a well defined vibrational progression in the neutral with an energy spacing of 343 ± 3 cm(-1). The adiabatic electron affinity was determined to be 1.775 ± 0.005 eV and assigned to the X(1)Σ(+)←X(2)Σ(+) transition between the anionic and neutral ground states. Franck-Condon simulations performed on density functional theory optimized geometries assisted the assignment of linear geometries to the neutral and anion and the observed vibrational progression to that of the Au-C4H stretch.

Geometries and stabilities of the carbon clusters with the rhodium impurity: a computational investigation

A density functional study of the RhCn(n = 1-6) clusters with different spin states has been carried out systematically by using the B3LYP/Lan2DZ method. The equilibrium geometries associated with total energies and natural populations of RhCn (n = 1-6) clusters are calculated and presented. Stabilities and electronic properties are discussed in detail. The relative stabilities in term of the calculated fragmentation energies show that the lowest-energy RhCn clusters with rhodium atom being located at terminal of carbon chain are the linear geometries and the ground states of the RhCn clusters alternate between doublet (for n-odd members) and quartet (for n-even members) states. Furthermore, the calculated fragmentation energies of the RhCn show strong even-odd alternations: the RhCn clusters with an odd number of carbon atoms are more stable than those with an even number ones. In addition, we comment on the charge transfer and chemical bonding properties within the clusters.

Structure and properties of the low-lying electronic states of CeC(2) and CeC(2)(+)

Theoretical studies on the electronic and thermodynamic properties of several electronic states of CeC(2) and CeC(2)(+) have been carried out employing state-of-the-art single- and multireference techniques. The ground and the low-lying electronic states of these two species have been found to possess C(2v) triangular structures. A (3)B(2) state has been found to be the ground state of CeC(2) while for CeC(2)(+) (2)A(2) is the ground state. The computed electron ionization energy is in excellent agreement with experiment. The experimentally observed thermodynamic properties (dissociation and atomization energies) of reactions involving CeC(2) dissociation are corrected using the computed gas-phase properties of the molecule and the partition functions. The bent triplet and singlet state of CeC(2) exhibit large dipole moments (7.0-10.5 D) and it is consistent with the ionic character (through dative charge transfer) of the cluster in ground and excited states.

Small ScCn Cyclic Clusters: A Density Functional Study of Their Structure and Stability

A theoretical study of the ScCn, ScCn+, and ScCn- (n = 1-10) cyclic clusters has been carried out employing the B3LYP density functional method. Predictions for several molecular properties that could help in their possible experimental characterization, such as equilibrium geometries, electronic structures, dipole moments, and vibrational frequencies, are reported. All ScCn cyclic clusters are predicted to have doublet ground states. For cationic clusters the ground state is alternate between singlets (n-even species) and triplets (n-odd members). In the case of anionic clusters the singlet-triplet separation is relatively small, with the singlets being favored in most cases. In general, even-odd parity effects are also observed for different properties, such as incremental binding energies, ionization energies, and electron affinities. For all neutral, cationic, and anionic clusters it is found that cyclic species are more stable than their open-chain counterparts. Therefore, cyclic structures are the most interesting possible targets for an experimental search of scandium-doped carbon clusters.

Small Carbon Clusters Doped with Early Transition Metals: A Theoretical Study of ScCn, ScCn+, and ScCn- (n = 1−8) Open-Chain Clusters

A theoretical study of the ScCn, ScCn+, and ScCn- (n = 1-8) open-chain clusters has been carried out. Predictions for their electronic energies, rotational constants, dipole moments and vibrational frequencies have been made using the B3LYP method with different basis set including effective core potentials, ECPs. For the ScCn open-chain clusters the lowest-lying states correspond to quartet states for n-odd members, whereas for n-even species the ground state is found to be a doublet. In the cationic and anionic species, the electronic ground state is found to be a singlet for even n and a triplet for odd n. An even-odd parity effect (n-even clusters being more stable than n-odd ones) is observed in neutral and charged clusters. Ionization energies and electron affinities also exhibit a clear parity alternation trend, with n-even clusters having higher values than n-odd ones.

Theoretical study of the electronic states of Nb4, Nb5 clusters and their anions (Nb4−,Nb5−)

Geometries and energy separations of the various low-lying electronic states of Nb(n) and Nb(n) (-) (n=4,5) clusters with various structural arrangements have been investigated. The complete active space multiconfiguration self-consistent field method followed by multireference singles and doubles configuration interaction (MRSDCI) calculations that included up to 52x10(6) configuration spin functions have been used to compute several electronic states of these clusters. The ground states of both Nb(4) ((1)A('), pyramidal) and Nb(4) (-) ((2)B(3g), rhombus) are low-spin states at the MRSDCI level. The ground state of Nb(5) cluster is a doublet with a distorted trigonal bipyramid (DTB) structure. The anionic cluster of Nb(5) has two competitive ground states with singlet and triplet multiplicities (DTB). The low-lying electronic states of these clusters have been found to be distorted due to Jahn-Teller effect. On the basis of the energy separations of our computed electronic states of Nb(4) and Nb(5), we have assigned the observed photoelectron spectrum of Nb(n) (-) (n=4,5) clusters. We have also compared our MRSDCI results with density functional calculations. The electron affinity, ionization potential, dissociation and atomization energies of Nb(4) and Nb(5) have been calculated and the results have been found to be in excellent agreement with the experiment.

Competition between linear and cyclic structures in monochromium carbide clusters CrCn− and CrCn (n=2–8): A photoelectron spectroscopy and density functional study

Photoelectron spectroscopy (PES) is combined with density functional theory (DFT) to study the monochromium carbide clusters CrCn- and CrCn (n = 2-8). Well-resolved PES spectra were obtained, yielding structural, electronic, and vibrational information about both the anionic and neutral clusters. Experimental evidence was observed for the coexistence of two isomers for CrC2-, CrC3-, CrC4-, and CrC6-. Sharp and well-resolved PES spectra were observed for CrCn- (n = 4,6,8), whereas broad spectra were observed for CrC5- and CrC7-. Extensive DFT calculations using the generalized gradient approximation were carried out for the ground and low-lying excited states of all the CrCn- and CrCn species, as well as coupled-cluster calculations for CrC2- and CrC2. Theoretical electron affinities and vertical detachment energies were calculated and compared with the experimental data to help the assignment of the ground states and obtain structural information. We found that CrC2- and CrC3- each possess a close-lying cyclic and linear structure, which were both populated experimentally. For the larger CrCn- clusters with n = 4, 6, 8, linear structures are the overwhelming favorite, giving rise to the sharp PES spectral features. CrC7- was found to have a cyclic structure. The broad PES spectra of CrC5- suggested a cyclic structure, whereas the DFT results predicted a linear one.