Theoretical investigation of the structures and properties of fluoromethyl peroxyl radicals

The equilibrium geometries, harmonic vibrational frequencies, charge distributions, spin density distributions, dipole moments, electron affinities (EAs), and C? O bond dissociation energies (BDEs) of HO, CH₃O, CH₂FO, CHF₂O, and CF₃O peroxyl radicals have been calculated using ab initio molecular orbital theory and density functional theory (DFT) at the B3LYP level. The C? H bond dissociation energies of the parent fluoromethanes have been calculated using the same levels of theory. Both the MP2(full) and B3LYP methods, using the 6‐31G(d,p) basis set, are found to be capable of accurately predicting the geometries of peroxyl radicals. Electron correlation accounts for ～25% of the C? H BDE of fluoromethanes and for ～50% of the C? O BDE of the corresponding peroxyl radicals. The B3LYP/6‐31G(d,p) method is found to be comparable to high ab initio levels in predicting C? O BDEs of studied peroxyl radicals and C? H BDEs of the parent alkanes. The progressive fluorine substitution of hydrogen atoms in methyl peroxyl radicals results in shortening of the C? O bond, lengthening of the O? O bond, an increase (decrease) of the spin density on the terminal (inner) oxygen, a decrease in the dipole moments, and an increase in electron affinities. Both C? O BDEs and EAs of peroxyl radicals (RO) correlate well with Taft σ* substituent constants for the R group in peroxyl radicals. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Ab initio and DFT investigation of fluorinated methyl hydroperoxides: Structures, rotational barriers, and thermochemical properties

Ab initio and density functional theory (DFT) calculations have been performed on CH₂FOOH, CHF₂OOH, CF₃OOH, CF₂ClOOH, and CFCl₂OOH. Geometries of stable conformers are optimized at the MP2(FULL)/6-31G(d,p) and B3LYP/6-31G(d,p) levels of theory. The enthalpies of formation () and the ROOH, ROOH, and ROOH bond dissociation enthalpies (BDEs) are estimated for each of the studied hydroperoxides using the calculated reaction enthalpies () of the adopted isodesmic reactions. The results show that the progressive fluorine substitution of hydrogen atoms in methyl group results in an increase in each of BDE(OH), BDE(OO), and BDE(CO). This has been explained in terms of the stabilizing influence of fluorine-substituted methyl groups. However, the replacement of F by Cl when going from CF₃OOH to CFCl₂OOH leads to a decrease in both BDE(OO) and BDE(CO). Potential energy barriers for internal rotation about CO and OO are calculated at the B3LYP/6-31G(d,p) level for each of the studied hydroperoxides.     

Ab initio and DFT study of the electronic structures and spectroscopic properties of pyrene ligands and their cyclometalated complexes

Two ligands 1‐diphenylphosphinopyrene (1‐PyP) ( L ₁ ), 1,6‐bis(diphenylphosphino)‐pyrene (1,6‐PyP) ( L ₂ ) and their cyclometalated complexes [Pt(dppm)(1‐PyP‐H)]⁺ ( 1 ), [Pt₂(dppm)₂(1,6‐PyP‐H₂)]²⁺ (dppm = bis(diphenylphosphino)methane ( 2 ), and [Pd(dppe)(1‐PyP‐H)⁺ (dppe = bis(diphenylphosphino)ethane) ( 3 ) are investigated theoretically to explore their electronic structures and spectroscopic properties. The ground‐ and excited‐state structures are optimized by the density functional theory (DFT) and single‐excitation configuration interaction method, respectively. At the time‐dependent DFT (TDDFT) and B3LYP level, the absorption and emission spectra in solution are obtained. As revealed from the calculations, the lowest‐energy absorptions of 1 and 3 are attributed to the mixing ligand‐to‐metal charge transfer (CT)/intraligand (IL)/ligand‐to‐ligand CT transitions, while that of 2 is attributed to the IL transition. The lowest‐energy phosphorescent emissions of the cyclometalated complexes are attributed to coming from the ³ILCT transitions. With the increase of the spin‐orbit coupling effect, the phosphorescence intensities and the emissions wavelength are correspondingly increased. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Ab initio study of the transition-metal carbene cations

The geometries and bonding characteristics of the first-row transition-metal carbene cations MCH_2~ were investigated by ab initio molecular orbital theory (HF/LANL2DZ). All of MCH_2~ are coplanar. In the closed shell structures the C bonds to M with double bonds; while in the open shell structures the partial double bonds are formed, because one of the σ and π orbitals is singly occupied. It is mainly the π-type overlap between the 2p_x orbital of C and 4p_x, 3d_(xz), orbitals of M~ that forms the π orbitals. The dissociation energies of C—M bond appear in periodic trend from Sc to Cu. Most of the calculated bond dissociation energies are close to the experimental ones.     

Density functional theory (DFT) and ab initio investigations of the electronic and molecular structures of the monomer and the dimer of trimethylaluminium

The electronic and molecular structures of the monomer and dimer of trimethylalu-minium have been studied using density functional theory and ab initio MP2 method. The optimized geometry of the monomer Al(CH3)3 is of C3h symmetry, whereas that of the dimer [A1(CH3)3]2 contains a carbon-bridged four-membered ring structure with C2h symmetry. The hydrogen-bridged six-membered ring structure is found to be unstable. The calculated dimerization energy for the four-membered ring structure is 78 kJ/mol, in close proximity to the experimental value of 85.27 kJ/mol.     

嵌锂石墨充电机制的abinitio和DFT理论研究

用ab initio/HFt DFT/B3LYP方法探究了在锂离子二次电池中锂离子在石墨负 电极材料里可逆脱过程。理论计算结果表明，嵌锂石墨LIG充放电机制是锂在石黑 碳层间可闹乱子嵌脱，同时伴随着锂与碳层间发生电荷连续转移和碳层堆积方式改 变的协同过程；计算结果也明确证实，嵌锂石墨嵌入脱出锂离子的过程就是锂离子 二次电池储存与释放能量的过程，提出的嵌锂石墨充放电机制较好地丰富了固体电 解质相界面SEI机理和单电子还原机理。     

8-羟基喹啉铝光电性质的Ab initio和DFT研究

利用abinitioHF和密度泛函理论B3LYP等方法,对金属有机配合物8-羟基喹啉铝(AlQ₃)进行几何结构优化,探索分子内部电子跃迁的机理.结果表明,电子从基态跃迁到低激发态时主要为π-π^*跃迁;电荷从含氧的苯酚环转移至含氮的吡啶环上,包括两环之间C→C转移和O→N转移,与金属离子关系不大.考虑到配体对发光性质的贡献,进一步设计了3种AlQ₃的衍生物.     

Ab initio and DFT modeling of stereoselective deamination of aziridines by nitrosyl chloride

The stereochemical course of the deamination of cis‐2,3‐dimethylaziridine by nitrosyl chloride was investigated at the QCISD/6‐31G(d) level. Calculations reveal that the reaction takes place in two steps. In the first step, the reactants form a pre‐reactive complex, followed by a spiro‐type bicyclic transition state, which on dissociative cycloelimination gives the N‐nitrosoaziridine intermediate. In the second step, this intermediate undergoes cycloreversion through a slightly asynchronous concerted transition state to form an alkene with the same stereochemistry, which is in total agreement with experiment. In the whole reaction, the denitrosation step is found to be rate‐determining. For comparison, geometry optimizations and energies were also obtained at the B3LYP/6‐31G(d) level. It was found that the B3LYP energy results differed significantly from the QCISD ones. To analyze the reason for this difference, B3LYP calculations were repeated by varying the contribution of exact exchange in the Becke functional. With respect to the QCISD results, it has been shown that the functional with 0% exact exchange yields the best activation barriers, whereas the functional with 30% exact exchange is the most suitable one to carry out the complexation and reaction energy calculations. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Ab initio study of sphere-like mesogen properties

Sphere-like compound C8H17Si(OPhC12H25)3N (1) forms mesophases. In order to investigate the relationship between molecular structure and liquid crystal properties, structural studies are carried out on the model molecules of compound 1 and its substituted derivatives using ah initio calculations. The results show that the cyano or chloro substituted tribenzosilatrane compounds R1Si(OPhR2 )3N (R1 R2 = CN or Cl) have much bigger dipole moments or anisotropy of polarizability and more like sphere than the corresponding alkyl substituted compounds. Cyano or chloro substituted tribenzosilatranes would be better candidates for sphere-like meso-gens.     

Ab initio multireference investigation of disjoint diradicals: singlet versus triplet ground states

We present improved virtual orbital (IVO) complete active space (CAS) configuration interaction (IVO‐CASCI) and IVO‐CASCI‐based multireference Møller–Plesset perturbation theory (MRMPPT) calculations with an aim to elucidate the electronic structure of tetramethyleneethane (TME) in its lowest singlet and triplet state and to quantify their order and extent of splitting. The potential surfaces of singlet and triplet states for the twisting of TME are also studied. We found that the triplet state is higher in energy than the singlet one in the whole range of twisting angles with the energy gap minimum at a twisting angle of about 45°. Harmonic vibrational frequencies of TME have also been calculated for both the states. We also report the ground to first excited triplet state transition energies. Our results are analyzed with respect to the results available in the literature to illustrate the efficacy of our methods employed. We also demonstrate that the spin character of the ground state of disjoint, TME‐like diradicals can be manipulated by using appropriate selection of annulenic spacer to separate the allyl groups of TME.     

Ab initio investigation of water clusters (H2O)n (n = 2–34)

Various properties of typical structures of water clusters in the n = 2–34 size regime with the change of cluster size have been systematically explored. Full optimizations are carried out for the structures presented in this article at the Hartree–Fock (HF) level using the 6‐31G(d) basis set by taking into account the positions of all atoms within the cluster. The influence of the HF level on the results has been reflected by the comparison between the binding energies of (H₂O)_n (n = 2–6, 8, 11, 13, 20) calculated at the HF level and those obtained from high‐level ab initio calculations at the second‐order Møller–Plesset (MP2) perturbation theory and the coupled cluster method including singles and doubles with perturbative triples (CCSD(T)) levels. HF is inaccurate when compared with MP2 and CCSD(T), but it is more practical and allows us to study larger systems. The computed properties characterizing water clusters (H₂O)_n (n = 2–34) include optimal structures, structural parameters, binding energies, hydrogen bonds, charge distributions, dipole moments, and so on. When the cluster size increases, trends of the above various properties have been presented to provide important reference for understanding and describing the nature of the hydrogen bond. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Ab initio study of the complexes of first-row transition-metal ions with CH, CH_2, and CH_3

The geometries and bonding characteristics of the complexes of the first-row transition-metal ions with CH, CH_2 and CH_3 were investigated by ab initio molecular orbital theory. MCH~ and MCH_2~ are linear and coplanar, re spectively. Both of them are with obvious treble or double bond characteristics, but these multiple bonds are mostly "im perfect". The calculated bond dissociation energies of C--M~ , C=M~ and C≡M~ are mostly close to the experi mental values, and appear in similar periodic trends from Sc to Zn.     

Ab initio quality properties for macromolecules using the ADMA approach

We describe new developments of an earlier linear scaling algorithm for ab initio quality macromolecular property calculations based on the adjustable density matrix assembler (ADMA) approach. In this approach, a large molecule is divided into fuzzy fragments, for which quantum chemical calculations can easily be done using moderate-size "parent molecules" that contain all the local interactions within a selected distance. If greater accuracy is required, a larger distance is chosen. With the present extension of this approximation, properties of the large molecules, like the electron density, the electrostatic potential, dipole moments, partial charges, and the Hartree-Fock energy are calculated. The accuracy of the method is demonstrated with test cases of medium size by comparing the ADMA results with direct quantum chemical calculations.     

Structure of isolated and solvated peroxyl radicals

We have investigated the structure of HO₂ and a series of alkyl peroxyl radicals ROO using a variety of quantum mechanical methods. We first compute the geometries, vibrational frequencies, electronic charge distributions, and spin densities for the series of radicals considered in the gas phase. Significant differences with respect to previous calculations have been pointed out in a few cases. In particular, we show the fundamental importance of electronic correlation when computing net atomic charges and spin densities, which have generally been estimated in the litterature by means of Hartree–Fock SCF electronic densities. Solvation effects on the geometry and electronic structure have been estimated by carrying out self-consistent reaction field computations in a polarizable continuum environment with relative dielectric permittivity equal to that of liquid water. Large electronic polarization is predicted in such conditions. This may be important in order to understand reactive properties of the radicals in different media. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1039–1048, 1999     

Ab initio study on the electronic structures of styrene in the Franck-Condon region

The electronic structures of styrene in the Franck‐Condon region have been theoretically examined by means of ab initio complete active space self‐consistent field (CASSCF) and the second order multireference Møller‐Plesset calculations. The optimized structure of styrene in S₀ is planar but the torsional motion of the phenyl group is very floppy. The S₁ state is assigned to the local π–π* excitation within the benzene ring. On the other hand, S₂, above S₁ by 0.561 eV, is assigned to a state that resembles the so‐called V‐state of ethylene. The transition intensity of S₀–S₁ is weak, while that of S₀–S₂ is strong. This is in good agreement with the experimental absorption spectrum where the S₀–S₁ and S₀–S₂ transitions are in the energy range of 290–220 nm. The optimized geometry of S₁, characterized by an enlarged benzene ring and its vibrational analyses, further justifies the assignment of the S₁ state. © 2002 Wiley Periodicals, Inc. J Comput Chem 9: 928–937, 2002     

Ab initio and DFT theory studies of interaction of thymine with formaldehyde

In this article, the interaction of formaldehyde (FA) with thymine is theoretically investigated by computational chemistry methods. The optimization geometries and vibrational frequencies of FA, thymine and three complexes between thymine and FA have been calculated by using the density functional theory and ab initio methods at the B3LYP/6-311G(d, p) and MP2/6-311G(d, p) levels. The NBO and AIM methods are used to analyse interaction as well. Conformers (A), (B) and (C) are cyclic structures with C–H***O and N–H***O hydrogen bonds on a common plane. The corrected complex interaction energies of cyclic structures (A), (B) and (C) at MP2/6-311G(d, p) levels are −38.41, −26.94 and −26.01 kJ/mol, respectively. The order of stability is (A) > (B) > (C).     

Ab initio investigation of ground‐state properties of group‐12 fluorides

The performance of wavefunction‐based correlation methods in theoretical solid‐state chemistry depends on reliable Hartree–Fock (HF) results for infinitly extended systems. Therefore, we optimized basis sets of valence‐triple‐ζ quality based on HF calculations for the periodic system of group‐12‐metal difluorides. Scalar‐relativistic effects were included in the case of the metal‐ions by applying small‐core pseudopotentials. To assess the quality of the proposed basis sets, the structural parameters, bulk moduli as well as cohesive and lattice energies of the systems were evaluated at the HF and the density functional theory levels. In addition to these two mean‐field approaches and to assess further employment of our basis sets to wavefunction‐based correlation methods we performed periodic local MP2 computations. Finally, the possibilities of pressure induced structural phase transitions occurring in the ZnF₂, CdF₂, and HgF₂ were investigated. © 2014 Wiley Periodicals, Inc.