Theoretical studies on low-lying electronic states of cyanocarbene HCCN and its ionic states

Geometries of 10, 7, and 6 low-lying states of the HCCN neutral radical, its anion and cation, were optimized by using the complete active space self-consistent field (CASSCF) method in conjunction with the aug-cc-pVTZ basis set, respectively. Taking the further correlation effects into account, the second-order perturbations (CASPT2) were carried out for the energetic correction. Vertical excitation energies (T(v)) at the ground state geometry of the HCCN neutral radical were calculated for 11 states. The results of our calculations suggest that the spin-allowed transitions of HCCN at 4.179, 4.395, 4.579, 4.727 and 5.506 eV can be attributed to X(3)A' --> 2(3)A', X(3)A' --> (3)A', X(3)A --> 3(3)A', X(3)A' --> 2(3)A', and X(3)A' --> 3(3)A', respectively. The singlet-triplet splitting gap of HCCN is calculated to be 0.738 eV. The vertical and adiabatic ionization energies were obtained to compare with the PES data. The results we obtained were consistent with the available experiment results.     

Theoretical study on the electronic states of NaLi

Configuration interaction calculations have been carried out on electronic states of the NaLi molecule and the cation NaLi(+). Potential energy curves are presented for the lowest nine (1)Sigma(+), seven (1)Pi, four (1)Delta, eight (3)Sigma(+), seven (3)Pi, and four (3)Delta states of NaLi as well as for the lowest ten (2)Sigma(+), six (2)Pi, and two (2)Delta states of NaLi(+). The results of the present many-electron configuration interaction calculations on the cation are in support of previous core-polarization effective potential calculations. The present calculations on the NaLi molecule are complementary to previous theoretical work on this system, including recently observed electronic states that had not been calculated previously as well as an investigation of nonadiabatic effects leading to spectral perturbations. Furthermore, ab initio potential energy curves of the neutral and the ground state of the cation are employed to determine quantum defect that may be employed to generate potential energy curves for nd and (n+1)p (for n>3) Rydberg states of NaLi. The present results on the 3 (1)Pi and 4 (1)Pi states are in good agreement with recent experimental work, whereas on the basis of theoretical data, the recently observed state 5 (1)Pi is better described as 6 (1)Pi.     

Theoretical investigations of the electronic states of porphyrins. IV. Low-lying electronic states of bisammineporphinatoiron(II)

Ab initio CI calculations are reported on the lowest quintet, triplet, and singlet states of Fe^II(P) (NH₃)₂. The lowest singlet state has strong mixing between the configuration (d_xy² (d_π)⁴ and (d_xy)²(d_π)³e_gπ*. The lowest quintet is mixed between ⁶A_1g)d_π and (⁶A_1g)e_gπ*, where ⁶A_1g refers to the high-spin ferric configuration. We calculate many low-energy states as ³(π→π*) ring and metal triplet and quintet configurations [“triptriplets” and “tripquintets”]. The calculations also show low-energy charge-transfer configurations of ring anion excited quartets and ferric quartets and sextets [“quartquartets” and “quartsextets”]. The farthest red x,y-polarized bands of the experimental spectra of low-spin hemoproteins are identified as d_xy → e_gπ* or d_π → d mixed with d_π → d and the z-polarized bands are assigned as d_π → e_gπ*. The farthest red x,y-polarized bands of the high-spin hemoproteins are identified as excited quartsextet states. Picosecond transients observed in Fe^II(TPP) (pip)₂ are attributed to an initial ¹(d_π → e_gπ*) state, which inter-system crosses to high-spin states that lose one ligand.     

Theoretical and experimental studies of radiative lifetimes of excited electronic states in CO

The electronic dipole transition moment functions of the A ²Π-X ²Σ⁺, B ²Σ⁺-X ²Σ⁺ and B ²Σ⁺-A ²Π transitions and the dipole moment function of the X ²Σ⁺ state of CO⁺ have been calculated using large contracted CI wavefunctions. The computed transition moment functions together with experimental potential energy curves were used to obtain radiative lifetimes of the excited electronic states B ²Σ⁺ and A ²Π. Radiative lifetimes of vibrational levels of the X ²Σ⁺ state were derived from the calculated dipole moment function. The high-frequency deflection technique was used to obtain radiative lifetimes of the ν′ = 0, 1,2 and 3 vibrational levels of the B ²Σ⁺ state and also radiative lifetimes of individual rotational levels of ν′ =0. The calculated radiative lifetimes are shorter than the measured ones by about 10%. The experimental ν′ dependence is reproduced by theoretical calculation. The calculated radiative lifetimes for the A ²Π state are in excellent agreement with lifetimes measured with an ion trap technique.     

Theoretical investigations of the electronic states of porphyrins. III. Low-lying electronic states of porphinatoiron(II)

Ab initio configuration interaction calculations are reported on the lowest quintet, triplet, and singlet states of Fe^II(P). Due to the large number of states found, a catalog of the low-lying states is presented. Novel triplet and quintet charge-transfer states are reported as low as 1.3 eV. These states are d⁵ (S = 5/2) on the iron low-spin-coupled to the radical anion excited porphyrin ring (S = 1/2 or 3/2). Oscillator strengths originating from each of three low-energy triplet states are reported.     

Theoretical studies on the low-lying electronic states of the HSO neutral radical and its cation

Using the complete active space self-consistent field (CASSCF) method with large atomic natural orbital (ANO-L) basis set, four electronic states of the HSO neutral radical are optimized. The vertical transitions of the HSO neutral radical are investigated by using the same method under the basis set of ANO-L functions augmented with a series of adapted 1s1p1d Rydberg functions, through which eight valence states and eight Rydberg states are probed. Ionic states of the HSO neutral radical are extensively studied in both cases of the adiabatic and vertical ionization, from which the relatively complete understanding of ionization energies is given. To include further correlation effects, the second-order perturbation method (CASPT2) is implemented, and the comparison between CASSCF and CASPT2 methods is performed.     

Theoretical study on low-lying electronic states of NiH2

The low-lying electronic states of the NiH2 molecule were investigated by using the MCQDPT2 method. In order to accurately describe the strong correlation derived from the nickel 3d9 super-configuration, a set of diffuse secondary 3d' orbitals were included in the active space, yielding a large active space of 12 electrons in 13 orbitals. It is shown that the absolute minimum energy configuration of NiH2 is bent, in agreement with the experimental observation. The global ground state is 1A1 (or A1 in the spin-orbit coupling case), whereas the lowest linear state is 3Deltag (or 3g). Some other cheaper single-configurational and multi-configurational methods were also used to study both states, and their shortcomings are discussed. Our theoretical results suggest that the arrangement of the experimental frequencies of NiH2 and NiD2 may be incorrect.     

Theoretical studies on excited states of Ne2

Previously reported potential curves for 0 _g ^? (³ P ₀) and 0 _u ^? (³ P ₀) of Ne₂ obtained from large-scale configuration-interaction calculations supplemented by semiempirical spin-orbit calculations are compared with potential curves deduced from experimental studies by Beyer and Haberland. Although the agreement between curves is very good, the assignment of states is opposite.Ab initio spin-orbit coupling matrix elements were calculated based on large CI wavefunctions for states dissociating to Ne + Ne^*(3s). It was found that they hardly change between 5 and 20a₀.Ab initio spin-orbit corrected potential curves differ little from previous curves relying on the semiempirical treatment of spin-orbit coupling, and all former conclusions remain essentially unchanged.     

Theoretical characterization of the low-lying electronic states of NbC

We have studied the potential-energy curves and the spectroscopic constants of the ground and low-lying excited states of NbC by employing the complete active space self-consistent field method with relativistic effective core potentials followed by multireference configuration-interaction calculations. We have identified 23 low-lying electronic states of NbC with different spin multiplicities and spatial symmetries within 40,000 cm(-1). At the multireference single and double configuration interaction level of theory the 2sigma+ and 2delta states are nearly degenerated, with the 2delta state located 187 cm(-1) lower than the 2sigma+ state. The estimated spin-orbit splitting for the 2delta state results in a 2delta(3/2) ground state and A 2sigma+ which is placed 650 cm(-1) above the ground state, in reasonable agreement with the experimental result, 831 cm(-1). Our computed spectroscopic constants are in good agreement with experimental values although our results differ from those of a previous density-functional investigation of the excited states of NbC, mainly due to the strong multiconfigurational character of NbC. In the present work we have not only suggested assignments for the observed states but also computed more electronic states that are yet to be observed experimentally.     

Theoretical studies of ground and excited electronic states in a series of heteroleptic iridium complexes using density functional theory

A series of new heteroleptic iridium(III) complexes [Ir(C^?N)₂(N^?N)]PF₆ ( 1 ‐ 6 ) (each with two cyclometalating C^?N ligands and one neutral N^?N ancillary ligand, where C^?N = 2‐phenylpyridine (ppy), 5‐methyl‐2‐(4‐fluoro)phenylpyridine (F‐mppy), and N^?N = 2,2′‐dipyridyl (bpy), 1,10‐phenanthroline (phen), 4,4′‐diphenyl‐2,2′‐dipyridy (dphphen) were found to have rich photophysical properties. Theoretical calculations are employed for studying the photophysical and electrochemical properties. All complexes are investigated using density functional theory. Excited singlet and triplet states are examined using time‐dependent density functional theory. The low‐lying excited‐state geometries are optimized at the ab initio configuration interaction singles level. Then, the excited‐state properties are investigated in detail, including absorption and emission properties, photoactivation processes. The excited state of complexes is complicated and contains triplet metal‐to‐ligand charge transfer, triplet ligand‐to‐ligand charge transfer simultaneously. Importantly, the absorption spectra and emission maxima can be tuned significantly by changing the N^?N ligands and C^?N ligands. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Theoretical study on the low-lying electronic states of NiH and NiAt

The low-lying electronic states of NiH and NiAt are investigated by using multireference second-order perturbation theory with relativistic effects taken into account. The potential energy curves as well as the corresponding spectroscopic constants are reported. The results are grossly in good agreement with the available experimental data and should thus be very useful for guiding future experimental measurements. A cross comparison with other nickel monohalides NiX (X = F, Cl, Br, and I) reveals that the change in the spin-orbit splittings when going from lighter to heavier ligands results more from the state interaction than from the relativistic effects of the ligands.     

Theoretical evidence for bound electronic excited states of ozone

Extensive configuration interaction calculations (up to 1532 spin eigenfunctions) have been carried out on ozone with both minimal and extended bases. Vertical and adiabatic excitation energies to 14 excited states are reported, including seven states with vertical excitation energies less than 4 eV. Our calculations indicate that in addition to the ground state there are four other states of ozone (³B₂, ³A₂, ¹A₂ and ³B₁) bound with respect to dissociation to ground state O₂ and O (by 0.4, 0.3, 0.1 and 0.0 eV, respectively). With such small bonding energies, the current results cannot be said to show definitively (except perhaps for ³B₂) these four states to be bound with respect to O₂ + O. However, the theoretical evidence is sufficiently strong as to warrant careful experimental studies. Such bound excited electronic states could play important roles in the chemistry of the upper atmosphere and in the chemistry of oxygen discharge systems. One (or more) of these states may be responsible for the short-lived intermediate (‘ozone precursor’) recently observed in oxygen radiolysis.     

Theoretical studies on the potential energy surface and rovibrational states for the electronic ground state of carbonyl sulfide

A potential energy surface for the electronic ground state of carbonyl sulfide was optimized by using a self-consistent field-configuration interaction method and involving the recent observed vibrational band origins up to 8000 cm⁻¹ for the Σ state. The root mean square error for this refinement was found to be 0.27 cm⁻¹. The calculated quartic force constants from the refined potential are very close to the recent high level ab initio calculations. The vibrational energy levels for the Π and Δ states and for some isotopomers of carbonyl sulfide molecule were calculated to test the refined potential. The calculated energy levels are in good agreement with the experimental values.     

硫化反式聚异戊二烯电子性质的理论化学研究

应用量子化学计算方法,对反式聚异戊二烯本征态和硫化态结构的能量及电子性质等进行了计算.结果表明,当聚异戊二烯掺杂硫后,相邻两链之间的距离a⊥变窄,体系的总能量降低,从而使整个掺杂体系更加稳定.另外,在硫化聚异戊二烯分子中,S原子位于两个相邻聚异戊二烯链之间,并偏向于其中一个分子链的C C双键的一侧,即与相邻两链中相对应的两个C C双键形成π-p-π共轭体系,增加了电子在两个聚异戊二烯链间的流动性,从而使硫化的反式聚异戊二烯更加稳定.另外,根据固体能带理论,采用量子化学EHMO方法,对反式聚异戊二烯本征态和硫掺杂态的能带结构进行了计算,根据硫化前后能隙和带宽的变化,解释了反式聚异戊二烯掺杂后呈现电导率各向异性的原因.     

Theoretical investigation of structures and electronic states of a series of phenyl-capped oligothiophenes

The structures and electronic states of a series of phenyl-capped oligothiophenes (PnTs) and their ionic species were investigated by means of the density functional theory (DFT). The calculations were performed on the oligomers formed by n repeating units, where n ranges from 2 to 6, using the B3LYP/6-31G** level of theory. The results obtained show that the end-substitution plays a fine-tuning effect on the geometries, electronics, and excitation states. It was found that the oligomers in the doped state have more satisfactory structural and electronic characteristics for the conducting polymers. The conjugated system in the doped oligomers has more aromaticity, with expanded and planar chains. The calculated energy gap values between the frontal molecular orbitals for the PnTs indicate that with increasing the oligomer chain length, the conductive band gap decreases. The calculated ?rst excitation energies of the PnTs at the TD-B3LYP/6-31G** level reveal that the doped PnTs have lower excitation energies than the neutral states. The oligomer chains with a phenyl ring as the end-capped group display red shifts in their absorption spectra. The end-caped substituted oligothiophenes display better characteristics than the unsubstituted ones. It could be anticipated that the phenyl-caped substitution would be helpful to charge-carrier hopings between chains, and thereby, enhance the conductivity.     

Theoretical study of electronic properties of organic photovoltaic materials

It has been proved that fullerene derivatives, in which an oligophenylenevinylene (OPV) group is attached to C(60), present an interesting photophysical phenomenon and can be incorporated into photovoltaic cells. In these systems, the OPV acts as electron donor upon excitation, and then fullerene absorbs photoexcited electrons. These new organic semiconductor materials offer the prospect of lower manufacturing costs and they present several advantages: easy fabrication, large area, flexible and light weight devices when compared with inorganic counter parts. In the present theoretical study, oligomeric chains of p-phenylenevinylene (n-PPV, n = 3-8 units) and C(60)-OPV hybrids have been studied by density functional theory (DFT). Electronic properties such as electronic absorption and emission spectra were calculated in order to determinate how the increment of spectroscopic units affects their electronic behavior. These properties were carried out with time dependent-density functional theory (TD-DFT) and ZINDO semiempirical method. The theoretical calculations of the structural properties of n-PPV and fullerene-OPV hybrids were obtained using PBE1PBE/6-31G and ONIOM two-layered version, respectively. All calculations were done with Gaussian 03W program package.     

Theoretical study of the electronic excited states of tetracyanoethylene and its radical anion.

The low-lying electronic states of tetracyanoethylene (TCNE) and its radical anion were studied using multiconfigurational second-order perturbation theory (CASPT2) and extended atomic natural orbital (ANO) basis sets. The results obtained yield a full interpretation of the electronic absorption spectra, explain the spectral changes undergone upon reduction, give support to the occurrence of a bound excited state for the anionic species, and provide valuable information for the rationalization of the experimental data obtained with electron transmission spectroscopy.