Adiabatic electron affinities of ScC2 and ScC3 evaluated by a multiconfigurational approach

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.

Assignment of the photoelectron spectra of FeS3(-) by density functional theory, CASPT2, and RCCSD(T) calculations

The geometric structures of FeS(3) and FeS(3)(-) with spin multiplicities ranging from singlet to octet were optimized at the B3LYP level, allowing two low-lying conformations for these clusters to be identified. The planar D(3h) conformation contains three S(2-) atomic ligands (S(3)Fe(0/-)), whereas the C(2v) structure contains, in addition to an atomic S(2-) ligand, also a S(2)(2-) ligand that is side-on-bound to the iron cation: an η(2)-S(2)FeS conformation. Subsequently, energy differences between the various states of these conformations were estimated by carrying out geometry optimizations at the multireference CASPT2 level. Several competing structures for the ground state of the anionic cluster were recognized at this level. Relative stabilities were also estimated by performing single-point RCSSD(T) calculations on the B3LYP geometries. The ground state of the neutral complex was unambiguously found to be (5)B(2). The ground state of the anion is considerably less certain. The 1(4)B(2), 2(4)B(2), (4)B(1), and (6)A(1) states were all found as low-lying η(2)-S(2)FeS(-) states. Also, (4)B(2) of S(3)Fe(-) has a comparable CASPT2 energy. In contrast, B3LYP and RCCSD(T) mutually agree that the S(3)Fe(-) state is at a much higher energy. Energetically, the bands of the photoelectron spectra of FeS(3)(-) are reproduced at the CASPT2 level as ionizations from either the (4)B(2) or (6)A(1) state of η(2)-S(2)FeS. However, the Franck-Condon factors obtained from a harmonic vibrational analysis at the B3LYP level show that only the (4)B(2)-to-(5)B(2) ionization, which preserves the η(2)-S(2)Fe-S conformation, provides the best vibrational progression match with the X band of the experimental photoelectron spectra.

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.

A theoretical study of the TiC5 cluster

The geometric and electronic properties of the titanium carbide TiC(5) cluster in its neutral and anionic charge states have been investigated using density functional theory (DFT) at the B3LYP level. The nonplanar six-membered ring-type or "butterflylike" structures are found to be the equilibrium geometric structures of TiC(5) and TiC(5) (-). Time-dependent DFT is used in the calculation of the excited states. The theoretical assignment at the B3LYP level for the features in the photoelectron spectrum is given. All results obtained are in good agreement with the available experimental data.

Structure and Bonding in First-Row Transition Metal Dicarbide Cations MC2+

A theoretical study of the first-row transition metal dicarbide cations MC2+ (M=Sc-Zn) has been carried out. Predictions for different molecular properties that could help in their eventual experimental detection have been made. Most MC2+ compounds prefer a C2v symmetric arrangement over the linear geometry. In particular, the C2v isomer is specially favored for early transition metals. Only for CuC2+ is the linear isomer predicted to be the global minimum, although by only 1 kcal/mol. In all cases the isomerization barrier between cyclic and linear species seems to be very small (below 2 kcal/mol). The topological analysis of the electronic density shows that most C2v isomers are T-shaped structures. In general, MC2+ compounds for early transition metals have larger dissociation energies than those formed by late transition metals. In most cases the dissociation energies for MC2+ compounds are much smaller than those obtained for their neutral analogues. An analysis of the bonding in MC2+ compounds in terms of the interactions between the valence orbitals of the fragments helps to interpret their main features.

Structure and Bonding in First-Row Transition-Metal Dicarbides: Are They Related to the Stability of Met-cars?

First-row transition-metal dicarbides MC(2) (M=Sc-Zn) have been investigated by using quantum-mechanical techniques. The competition between cyclic and linear isomers in these systems has been studied and the bonding scheme for these compounds is discussed through topological analysis of electron density. All of the systems have been found to prefer a C(2v)-symmetric arrangement, although for ZnC(2) the energy difference between this and the linear isomer is rather small. In most cases the C(2v)-symmetric structure corresponds to a T-shaped structure, with the exceptions of TiC(2), CoC(2), and NiC(2) which have been shown to be true rings. A detailed analysis of the variation of the energy of the system with geometry has been carried out. An analysis of the bonding, taking into account the main interactions between the valence orbitals of both fragments, the M atom and the C(2) molecule, has allowed the main features of these compounds to be interpreted. A clear correlation between the dissociation energies of the first-row transition-metal dicarbides and the bonding energies of the corresponding met-cars was observed.

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.