Electronic structures of permethyloligosilane radical cations at the ground and low-lying excited states

The electronic structures at the ground and low-lying excited states of permethyloligosilane radical cations, Si_n(CH₃)_2n+2⁺ (n = 4-7), have been investigated using DFT and ab initio calculations. The calculations showed that positive charge (hole) is delocalized along the Si-Si main chain at the ground and first excited states. On the other hand, the hole is transferred to the methyl side-chain at the second and higher excited states. From these results, it was concluded that hole can move along the Si-Si main chain at thermal conditions. Also, it was predicted that intermolecular hole hopping takes place by photo-irradiation to the permethyloligosilane radical cation. The mechanism of hole transfer was discussed on the basis of the results.     

Improvement of scale factors for harmonic vibrational frequency calculations using new polarization functions

Density functional calculations were carried to improve the calculated CO vibrational frequencies for transition metal carbonyls. Two types of density functionals were studied, hybrid and generalized‐gradient methods. Using the simplex optimization method, new polarization functions for C and O atoms were obtained. With these new optimized functions, new scaling factors were obtained. The results reveal that, with the new polarization functions, the agreement between the calculated and the experimental values improves considerably. In general, the new scaling factors are very close to unit, with standard uncertainties close to ±0.006 cm^?1. The use of the new polarization functions allows more precise calculations of the transition metal carbonyl CO vibrational frequencies. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Si~2Cl~6分子的内旋转能垒和振动基频的理论研究

用从头算方法HF/6-31G^*^*和密度函方法B3LYP/6-31G^*^*,对Si~2Cl~6分子的平衡几何构型进行优化,优化的结果与实验结果吻合得较好.并用上述两种不同的方法计算Si~2Cl~6分子的内旋转能垒,结果分别为8.786和6.694kJ/mol,其中DFT方法的计算结果与实验结果4.18kJ/mol吻合得较好.对Si~2Cl~6分子的振动基频进行计算.用HF/6-31G^*^*SQM力场所计算的频率理论值与实验值的平均误差为7.3cm^-^1,用B3LYP/6-31G^*^*未标度的力场所计算的频率理论值与实验值的平均误差为6.0cm^-^1.该密度泛函方法(B3LYP/~6-31G^*^*)的理论计算值比用HF/6-31G^*^*标度后的SQM力场计算的频率与实验值(除Si--Si键扭转振动基频之外的11条振动基频)吻合得更好.并给出了Si--Si键扭转振动基频的预测值。     

The influence of ultrashort excitations on the vibrational dynamics in a diatomic molecule

The problem of vibrational wave packet dynamics in the system of two electronic states of a diatomic molecule, where the states are coupled by infinitely short light pulses, is solved. The electronic states were modeled by shifted harmonic oscillators with different frequencies. Exact expressions for the probability densities of the wave packets in the ground and excited states were derived. The spatial, spectral, and temporal characteristics of the wave packets, namely, the range of motion, spatial width, mean energy, spectral width (the mean number of vibrational states in a wave packet), and the autocorrelation function, were calculated as functions of the molecular parameters (the frequency ratio and the distance between the potential minima) and of the delay time between the light pulses. The possibility of controlling the mean energy and spectral width of the wave packets in the ground electronic state by varying the delay time is considered. It was shown that "squeezed" wave packets can be prepared in the ground electronic state if the upper electronic state is shallow.     

Ab initio potential energy surface and excited vibrational states for the electronic ground state of Li_2H

A 285-pomt multi-reference configuration-interaction involving single and double excitations ( MRS DCI) potential energy surface for the electronic ground state of L12H is determined by using 6-311G (2df,2pd)basis set.A Simons-Parr-Finlan polynomial expansion is used to fit the discrete surface with a x2 of 4.64×106 The equn librium geometry occurs at Rc=0.172 nm and,LiHL1=94.10°.The dissociation energy for reaction I2H(2A)→L12(1∑g)+H(2S) is 243.910 kJ/mol,and that for reaction L12H(2A')→HL1(1∑) + L1(2S) is 106.445 kl/mol The inversion barrier height is 50.388 kj/mol.The vibrational energy levels are calculated using the discrete variable representation (DVR) method.     

Ab initio and density functional theory study of the electronic structure of rhenium complexes with noninnocent dioxolene ligands: Localized vs delocalized valence states

The dioxolene type ligands (Diox) derived from ortho-quinones are the most widely studied redox noninnocent ligands existing in the dianionic (Cat), anion radical (SQ) or neutral (Q) forms although a highly delocalized electronic structure is also possible. For [ReO(Diox)₂PPh₃]⁻ ( 2 ) and [ReCl₃(Diox)PPh₃] ( 3 ) complexes, the Re^V-Cat₂ and Re^IV-SQ localized valence states were proposed on the basis of their XRD structures. To understand in detail the electronic structure of these complexes, we performed a series of the all-electron calculations at the DKH2-CASSCF/CASPT2 and DKH2-CASSCF/NEVPT2 levels taking into account scalar relativistic and spin-orbit effects. All calculations predicted that 2 has a singlet ground state with a predominant contribution of a single electronic configuration with doubly occupied molecular orbitals being pure o-quinone LUMOs of both Diox ligands that corresponds to the Re^V-Cat₂ valence state. Complex 3 has a triplet ground state with four electronic configurations contributing mainly into its wavefunction and differing by the occupation of bonding and antibonding combinations of the o-quinone LUMO and rhenium d-AO with nearly equal contributions. This leads to the empirical “metrical oxidation state” of dioxolene ligand being −1 that is usually referred to the Re^IV-SQ oxidation state. However, in fact, the negative charge on the Diox ligand is mainly provided by a pair of electrons on the bonding MO. The standard DFT calculations entirely fail to correctly predict the ground state multiplicity for 3 .     

Infrared vibrational spectra,electronic structures,and formation reactions of polypyrrolic mono‐ and bis‐actinyl complexes: A relativistic DFT study

The development of synthetic techniques has enabled synthesis and characterization of a series of mono and bis‐uranyl complexes of octadentate polypyrrolic macrocycles such as aryl‐lined H₄L^Ar and anthracenyl‐linked H₄L, which is complemented by theoretical investigation via extending to more toxic and radioactive transuranics. The relativistic density functional theory (DFT) study has been dedicated to twelve actinyl complexes supported by the H₄L ligand. The actinides include U, Np, and Pu elements, and either one or two is rendered in complexes with oxidation states of V or VI. Calculated symmetric/asymmetric An = O stretching vibrational frequencies show the decreasing trend along U, Np, and Pu, which is consistent with calculated bond orders. The hydrogen bonds between –yl endo‐oxo and remaining hydrogen atoms of pyrrolides in mononuclear complexes cause pronounced redshift of An = O vibrational frequencies compared to those in binuclear complexes, so does the reduction from hexa‐ to penta valent complexes. The electronic structures of actinyl complexes were calculated. For example, B‐ pyU^VI possesses low‐lying U(5f )‐character virtual orbitals, where f (δ) and f (?) orbitals occur in low‐energy region and π‐type ones are residing further high; the σ*(U = O) and σ(U = O) orbitals are significantly split over 7 eV. The previous experimental observation that the 1:1 reactions between uranyl salts and the macrocycle tend to give a mixture of bis‐ and mono‐uranyl complexes, with bis‐ the major product, has been corroborated by computational studies of the thermodynamics of the reactions.     

Ab initio potential energy surface and excited vibrational states for the electronic ground state of Li2H

A 285-point multi-reference configuration-interaction involving single and double excitations (MRS-DCI) potential energy surface for the electronic ground state of Li₂H is determined by using 6-311G (2df, 2pd) basis set. A Simons-Parr-Finlan polynomial expansion is used to fit the discrete surface with a X² of 4.64 × 10^-6. The equilibrium geometry occurs at R_e =0.172 nm and <LiHLi =94.10. The dissociation energy for reaction Li₂H(²A)⇑ Li₂(¹⌆_g)+H(²S) is 243.910 kJ/mol. and that for reaction Li₂H(²A)⇑HLi(¹be)+Li(²S) is 106.445 kJ/mol. The inversion barrier height is 50.388 kJ/mol. The vibrational energy levels are calculated using the discrete variable representation (DVR) method. Project supported by the National Natural Science Foundation of China (grant No. 29673029) and by the Special Doctoral Research Foundation of the State Education Commission of China.     

Prediction of spectroscopic constants for diatomic molecules in the ground and excited states using time-dependent density functional theory

Spectroscopic constants of the ground and next seven low-lying excited states of diatomic molecules CO, N2, P2, and ScF were computed using the density functional theory SAOP/ATZP model, in conjunction with time-dependent density functional theory (TD-DFT) and a recently developed Slater type basis set, ATZP. Spectroscopic constants, including the equilibrium distances r(e), harmonic vibrational frequency omega(e), vibrational anharmonicity omega(e)x(e), rotational constant B(e), centrifugal distortion constant D(e), the vibration-rotation interaction constant alpha(e), and the vibrational zero-point energy E(n)0 were generated in an effort to establish a reliable database for electron spectroscopy. By comparison with experimental values and a similar model with an established larger Slater-type basis set, et-QZ3P-xD, it was found that this model provides reliably accurate results at reduced computational costs, for both the ground and excited states of the molecules. The over all errors of all eight lowest lying electronic states of the molecules under study using the effective basis set are r(e)(+/-4%), omega(e)(+/-5% mostly without exceeding +/-20%), omega(e)x(e)(+/-5% mostly without exceeding 20%, much more accurate than a previous study on this constant of +/-30%), B(e)(+/-8%), D(e)(+/-10%), alpha(e)(+/-10%), and E(n)0(+/-10%). The accuracy obtained using the ATZP basis set is very competitive to the larger et-QZ3P-xD basis set in particular in the ground electronic states. The overall errors in r(e), omega(e)x(e), and alpha(e) in the ground states were given by +/-0.7, +/-10.1, and +/-8.4%, respectively, using the efficient ATZP basis set, which is competitive to the errors of +/-0.5, +/-9.2, and +/-9.1%, respectively for those constants using the larger et-QZ3P-xD basis set. The latter basis set, however, needs approximately four times of the CPU time on the National Supercomputing Facilities (Australia). Due to the efficiency of the model (TD-DFT, SAOP and ATZP), it will be readily applied to study larger molecular systems.     

DFT and TDDFT investigations on the ground and excited states for polynuclear platinum(Ⅱ) complexes containing the rigid phenylacetylide ligand

We have studied the ground and excited states of the three dendritic polynuclear Pt(Ⅱ) complexes 1-[Cl(PH3)2PtC≡C]-3,5-[HC≡C]C6H3 (1), 1,3-[Cl(PH3)2PtC≡C]2-5-[HC≡C]C6H3 (2), and 1,3,5-[Cl(PH3)2- PtC≡C]3C6H3 (3), by using the B3LYP and UB3LYP methods, respectively. TDDFT approach with the PCM model was performed to predict the emission spectra properties of 1-3 in CH2Cl2 solution. We first predicted the excited-state geometries for the three complexes. With the change of the number of Pt(Ⅱ) atom, 1-3 show the different geometry structures in both the ground and excited states; furthermore, the increase of the metal density from 1 to 3 results in the red shift of the lowest-energy emissions along the series. The luminescent properties of 1 are somewhat different from those of 2 and 3. The emission properties of 2 and 3 are richer than 1. Our conclusion can give a good support for designing the high efficient luminescent materials.     

Scaling factors for vibrational frequencies and zero-point vibrational energies of some recently developed exchange-correlation functionals

The scaling factors for the vibrational frequencies and zero-point vibrational energies evaluated at various combinations of recently developed exchange-correlation functionals and various basis sets are reported. The exchange-correlation functionals considered are B972, B98, HCTH, OLYP, O3LYP, G96LYP, PBE0 and VSXC functionals; the basis sets employed are 3-21G, 6-31G*, 6-31G**, 6-31+G, 6-311G*, 6-311G**, 6-311G(df,p), 6-311+G(df,p), cc-pVDZ and aug-cc-pVDZ. The experimental harmonic frequencies of 122 small molecules and the zero-point vibrational energies of 39 small molecules are used to determine the scaling factors through the least-square fitting procedure. It was found that the scaling factors do not depend significantly on the basis sets considered. The vibrational frequency scaling factors evaluated by using the B98 and PBE0 functionals are recommended on the basis of smallest root mean square error. The zero-point vibrational energy scaling factors evaluated from the B972 functional with Pople's double-zeta basis set and the HCTH functional with Pople's triple-zeta basis set are recommended on the basis of smallest root mean square error.     

DFT方法研究间苯二酚-甲醛气凝胶单体分子性质与振动频率

用B3LYP密度泛函方法在6-311G**基组水平上计算了单元、二元羟甲基间苯二酚的分子体积和振动频率,通过理论计算与实验结果的比较,探讨了间苯二酚-甲醛气凝胶形成的微观机理,具体分析了各振动模式的归属和同位素取代对振动频率的影响.     

Electronic properties of the low‐lying spin states of dimethylnitrosamine coordinated to Fe(III) heme models: An ab initio study

The unusual O‐coordination mode of nitrosamines to Fe(III) heme models has been observed in the bis(dimethylnitrosamine)(meso‐tetraphenylporphyrinate)iron(III) cation. For the first time, this latter as well as the simpler bis(dimethylnitrosamine)(porphinate)iron(III) heme model cations have been studied through ab initio methods. The sextet, quartet, and doublet spin states of both cations have been studied through single‐point calculations based on the experimental (X‐ray) geometry. Their energies, charges, and spin densities have been analyzed. The obtained results (at the UHF/cc‐pVDZ and ROHF/cc‐pVDZ levels) indicate that the peripheral benzene rings are of secondary importance for the coordination of dimethylnitrosamine to the Fe(III) porphyrin core. The obtained energy ordering is sextet < quartet < doublet, at all computational levels. The UHF, ROHF, and UMP2 results indicate an excess of alpha spin density around the Fe atom, a low covalency for the Fe? O bond and a substantial charge transfer to the Fe atom. Our best estimates [obtained at ROMP2 level with the mixed cc‐pVDZ/cc‐pVTZ‐DK(Fe) basis set] for the energy differences (in eV) between the three spin states considered are 0.929 for the sextet‐quartet gap and 0.812 for the quartet‐doublet gap, which indicate that the spin crossover (at room temperature) is very unlikely. These results represent the substantial decrease in the uncorrelated values. The implications of spin contaminations at the UHF and UMP2 levels for subsequent geometry optimizations to be performed in the smaller cation have also been discussed. © 2013 Wiley Periodicals, Inc.     

Contracted well-tempered Gaussian basis sets in SCF calculations on the ground and excited electronic states of neutral and ionized diatomic molecules containing first-row atoms

Summary Calculations were done on ground and excited states of C₂, C ₂ ⁺ , C ₂ ^– , N₂, N ₂ ⁺ , O₂, O ₂ ⁺ , O ₂ ^– , CO, CO⁺, CO²⁺, and CO^– using contracted well-tempered basis sets. The (14s 10p) basis sets were augmented with threed, one or twof, and oneg functions. Total energies, orbital energies, and spectroscopic constants were compared with the best available computational data.     

Electronic and vibrational linear and nonlinear polarizabilities of Li@C60 and [Li@C60]+

Electronic and vibrational nuclear relaxation (NR) contributions to the dipole (hyper)polarizabilities of the endohedral fullerene Li@C(60) and its monovalent cation [Li@C(60)](+) are calculated at the (U)B3LYP level. Many results are new, while others differ significantly from those reported previously using more approximate methods. The properties are compared with those of the corresponding hypothetical noninteracting systems with a valence electron transferred from Li to the cage. Whereas the NR contribution to the static linear polarizabilities is small in comparison with the corresponding electronic property, the opposite is true for the static hyperpolarizabilities. A relatively small, but non-negligible, NR contribution to the dc-Pockels effect is obtained in the infinite frequency approximation.     

Ro‐vibrational studies of diatomic molecules in a shifted Deng–Fan oscillator potential

Bound‐state spectra of shifted Deng‐Fan oscillator potential are studied by means of a generalized pseudospectral method. Very accurate results are obtained for both low as well as high states by a nonuniform optimal discretization of the radial Schrödinger equation. Excellent agreement with literature data is observed in both s‐wave and rotational states. Detailed variation of energies with respect to potential parameters is discussed. Application is made to the ro‐vibrational levels of representative diatomic molecules (H₂, LiH, HCl, CO). Nine states having are calculated with good accuracy along with 15 other higher states for each of these molecules. Variation of energies with respect to state indices n, show behavior similar to that in the Morse potential. Many new states are reported here for the first time. In short, a simple, accurate, and efficient method is presented for this and other similar potentials in molecular physics. © 2013 Wiley Periodicals, Inc.     

Electronic and vibrational properties of fluorenone in the channels of zeolite L

Fluorenone (C13H8O) was inserted into the channels of zeolite L by using gas-phase adsorption. The size, structure, and stability of fluorenone are well suited for studying host-guest interactions. The Fourier transform IR, Raman, luminescence, and excitation spectra, in addition to thermal analysis data, of fluorenone in solution and fluorenone/zeolite L are reported. Normal coordinate analysis of fluorenone was performed, based on which IR and Raman bands were assigned, and an experimental force field was determined. The vibrational spectra can be used for nondestructive quantitative analysis by comparing a characteristic dye band with a zeolite band that has been chosen as the internal standard. Molecular orbital calculations were performed to gain a better understanding of the electronic structure of the system and to support the interpretation of the electronic absorption and luminescence spectra. Fluorenone shows unusual luminescence behavior in that it emits from two states. The relative intensity of these two bands depends strongly on the environment and changes unexpectedly in response to temperature. In fluorenone/zeolite L, the intensity of the 300 nm band (lifetime 9 micros) increases with decreasing temperature, while the opposite is true for the 400 nm band (lifetime 115 micros). A model of the host-guest interaction is derived from the experimental results and calculations: the dye molecule sits close to the channel walls with the carbonyl group pointing to an Al3+ site of the zeolite framework. A secondary interaction was observed between the fluorenone's aromatic ring and the zeolite's charge-compensating cations.