Theoretical Study Of Geometry Research Articles

Geometries, Electronic Structures, and Energetic Parameters of the first-row transition metal doped aluminum clusters Al16M

A theoretical study of geometry, stability, electronic structure, and magnetic property of neutral Al16M clusters with M being a first-row 3d transition metal atom, including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, are investigated in this theoretical study using quantum chemical approaches. The neutral Al16M clusters favor three kind of structures based on pure Al17 framework, including two exohedral doped isomers and one endohedral doped structure. There is a competition between the endoheral and the exohedral structures of Al16M with M being Ni, Cu, and Zn. The thermodynamic stability of encapsulated structure Al16Ni is confirm by the calculated average binding energy and embedded energy values. DFT calculation, however, indicate that the transition metal doping reduces the ionization potential of the pure aluminum clusters. Based on NBO calculations, a comprehensive picture of magnetic behavior is shown for Al16M clusters. Remarkably, the magnetism of the encapsualated Ni dopant is quenched in Al16 cage. Moreover, NBO calculations found that the 50-electron shells are completely preserved in both clusters Al16Sc and Al­16Ti and the remaining unpaired electron(s) localize(s) mainly on 3d atomic orbitals of the transition metal dopant.

Theoretical study of geometry and electronic properties of medium-sized doped clusters Li2Bn0/− (n = 1–12)

Theoretical study of geometry and electronic properties of medium-sized doped clusters Li2Bn0/− (n = 1–12)

Theoretical study of geometry, stability and properties of Al and AlSi nanoclusters

Geometry, stability, and properties of Al n (n = 1–13) and Al n Si m (n + m = 5–7) nanoclusters were investigated by density functional theory. We found that while geometry of some clusters change significantly by substituting of Al atom(s) with Si atom(s) the geometry of some others remain without significant variation. The relative stability of clusters was discussed on the basis of binding energy per atom, fragmentation energy, and second-order difference of cluster energies. Our results reveal that Al7 is the most stable cluster among pure clusters. For Al n Si m clusters, it is observed that Al2Si3 (60 % Si), and Al4Si2 (33.33 % Si) are the most stable clusters. The reactivity of Al n and Al n Si m nanoclusters was also investigated on the basis of chemical hardness. The most important feature of chemical hardness is its oscillating behavior as a function of atomic percentage of Si indicating that the reactivity of Al n Si m clusters strongly depends on the composition of cluster.

Theoretical study of geometry and nucleophilicity of the exocyclic methylene in five-membered ring cyclic ketene acetals, neutral and protonated, containing pnictogen and chalcogen heteroatoms

A series of neutral and protonated five-membered ring cyclic ketene acetals have been examined computationally for any trends in nucleophilicity in the exocyclic methylene and for their ground state geometries. A total of 58 different species were examined, 29 neutral molecules and the corresponding 29 protonated species. The heteroatoms that were used in the heterocyclic ring were a combination of nitrogen, phosphorus, and arsenic from the pnictogen family and oxygen, sulfur, and selenium from the chalcogen family. All geometries were initially optimized at using density functional theory and all stationary points were confirmed to be either minima or transition states through vibrational analysis. All the geometries were consequentially optimized using Moller–Plesset second order perturbation theory with a polarized triple zeta basis set. The main focus of the study was the nucleophilicity of the exocyclic methylene carbon atom and its dependence on heteroatom substitution. As probes for nucleophilicity, the proton affinities of the neutral species, the bond lengths of the exocyclic double bond, and atomic charges were used. The study also resulted in some interesting molecular geometries.

Theoretical Study of Geometries and Electronic Transition of Color-Switching Molecules: Tetra-Aza Macrocycle and Its Zinc Complexes

Abstract Tetra-aza macrocycles containing 2,2′-bipyridine moieties fascinatingly undergo color-switching. Here, a tetra-aza macrocycle was analyzed as well as its zinc complexes from the viewpoint of ab initio molecular orbital (MO) and density functional theory (DFT) calculations. As a result of systematic geometry searches, obtained geometries of stable conformers were consistent with the structural formula developed from the experimental results. Transition energies and oscillator strengths of the stable conformers were calculated based on time-dependent DFT (TDDFT) and compared with the experimental data. The effect of the solvent was considered by using a polarization continuum model (PCM). The calculated transition energies qualitatively agreed with the experimental UV spectra. Structural changes upon complexation and the features of the molecular orbitals related to the transition from the ground state to the excited states are discussed.

Theoretical Study of Geometries and Electronic Structures of Solid Oxygen under High Pressures

We have theoretically studied the geometries and electronic structures of solid oxygen under high pressures. The calculations were performed by using a first-principles method based on the density-functional theory combined with a scissors method to correct the energy gap appropriately. We found that the molecular dissociation does not occur at the metallization pressure. Furthermore, we found that spin polarization is largely decreased by the application of pressure and almost disappears at the metallization pressure.

A theoretical study of geometry and transition moment directions of flexible fluorescent probes--acetoxy derivatives of phenylanthracene

Recently synthesized acetoxy derivatives of phenylanthracene are highly fluorescent compounds. They may be used as laser dyes and fluorescent probes of a biomolecular structure [J.R. Heldt, J. Heldt and K. Aleksandrzak, J. Photochem. Photobiol. A: Chem., 81 (1994) 79]. The rational application of these compounds in spectroscopic studies, e.g. fluorescence anisotropy measurements, requires detailed knowledge of the geometries and the transition moment directions. This contribution presents the first systematic INDO/S semiempirical study of the singlet absorption spectra of the series of the following molecules: anthracene, phenylanthracene, 9-acetoxy-10-(4′-phenyl)anthracene, 9-acetoxy-10-(4′-acetoxyphenyl)anthracene, 9-acetoxy-10-(2′-acetoxyphenyl)anthracene ( C2FAC ). We put special emphasis on the calculations of the directions of absorption transition moment to all relevant singlet exited states and their relations to the geometries of the dyes. The geometries of all compounds were optimized with the Austin Model 1 (AM1) method and compared with the available X-ray data. Additionally, the barrier to rotation of the acetoxy group attached to the phenyl ring was calculated using the AM1 Hamiltonian. Our results indicate that spectra of derivatives studied do not depend on the location of the acetoxy groups, but the hydrodynamic shape of the C2FAC molecule may be different than the other phenylanthracenes. The calculated geometries are in reasonable agreement with the experimental ones.

A theoretical study of geometry and transition moment directions of flexible fluorescent probes—acetoxy derivatives of phenylanthracene

Recently synthesized acetoxy derivatives of phenylanthracene are highly fluorescent compounds. They may be used as laser dyes and fluorescent probes of a biomolecular structure [J.R. Heldt, J. Heldt and K. Aleksandrzak, J. Photochem. Photobiol. A: Chem., 81 (1994) 79]. The rational application of these compounds in spectroscopic studies, e.g. fluorescence anisotropy measurements, requires detailed knowledge of the geometries and the transition moment directions. This contribution presents the first systematic INDO/S semiempirical study of the singlet absorption spectra of the series of the following molecules: anthracene, phenylanthracene, 9-acetoxy-10-(4′-phenyl)anthracene, 9-acetoxy-10-(4′-acetoxyphenyl)anthracene, 9-acetoxy-10-(2′-acetoxyphenyl)anthracene ( C2FAC). We put special emphasis on the calculations of the directions of absorption transition moment to all relevant singlet exited states and their relations to the geometries of the dyes. The geometries of all compounds were optimized with the Austin Model 1 (AM1) method and compared with the available X-ray data. Additionally, the barrier to rotation of the acetoxy group attached to the phenyl ring was calculated using the AM1 Hamiltonian. Our results indicate that spectra of derivatives studied do not depend on the location of the acetoxy groups, but the hydrodynamic shape of the C2FAC molecule may be different than the other phenylanthracenes. The calculated geometries are in reasonable agreement with the experimental ones.

ChemInform Abstract: Theoretical Study of Geometries and Dipole Moments of AsX3 and SbX3 (X: F, Cl, Br, and I) Molecules

ChemInform Abstract: Theoretical Study of Geometries and Dipole Moments of AsX3 and SbX3 (X: F, Cl, Br, and I) Molecules

Theoretical study of geometries and dipole moments of AsX3 and SbX3 (X=F, Cl, Br, and I) molecules

Theoretical study of geometries and dipole moments of AsX3 and SbX3 (X=F, Cl, Br, and I) molecules

Theoretical study of geometries and 1H-chemical shifts of cycloarenes

The geometries of the cycloarenes 1–6 with 9–12 annelated benzene rings are determined by means of a π-SCF force-field approach. 1H-chemical shifts are calculated by taking into account ring current and local anisotropic contributions. The importance of annulenoid resonance structures is discussed.

Benzannelated annulenes -12. : Theoretical study of geometries and 1H chemical shifts of benzannelated [14] annulenes

The geometries and the 1H chemical shifts of dihydropyrene 1 and its benzannelated derivatives 2 – 8 have been studied by means of semiempirical quantum chemical procedures. The calculated bond lengths of 1 and proton shifts of 1 – 5 are in good accord with the corresponding experimental values. We show that monobenzannelation in 2 – 4 causes considerable bond length alternation in the [14] perimeter and hence reduced diatropocity. The same is true for the phenanth-fused dibenzannelated compounds 4 and 7 . On the other hand we report evidence that anth-fused dibenzannelated dihydropyrenes 5 , 6 , and 8 should be characterized by symmetric geometrical structures without significant bond length alternation thus leading to enhanced diatropicity.