Mutsumi Tomonari

Simplified sum-over-states calculations and missing-orbital analysis on hyperpolarizabilities of benzene derivatives

Abstract The simplified sum-over-states (SOS) and missing-orbital analysis methods are introduced. The former aims to calculate the molecular polarizabilities in the framework of ab initio SCF theory, and the latter to analyze the calculated polarizabilities. The utility of the combination of these methods is demonstrated for the benzene derivatives, e.g. p -nitroaniline (PNA) and p -cyanoaniline (PCA). The calculated first-order hyperpolarizabilities (β) agree well with those of both CPHF calculations and experimental results. The missing-orbital analysis shows that β for PCA is contributed by both forward and backward charge transfer (CT) related to “out-of-plane” and “in-plane” orbitals, respectively. In contrast, β for PNA is confirmed to be explained fully by the conventional two-state model characterized by strong forward CT.

Molecular hyperpolarizability components βzzz and βzxx under directional extensions of π conjugation: missing-orbital analysis and simplified sum-over-states calculations

Abstract The application of missing-orbital analysis to molecular hyperpolarizability β obtained by a simplified sum-over-states calculation, allows one to study the effects of the π conjugation extension on both diagonal β zzz and off-diagonal β zxx components for C 2v molecules (the z -axis being the principal one). Extension of the z -length in aminonitropolyacetylenes by increasing the number of acetylene units increases β zzz but β zxx remains unchanged. Conversely, β zxx increases significantly with only a slight increase in β zzz if the π conjugation is extended mainly in the x -direction for 1,3-diamino-4,6-dinitrobenzene by replacing benzene with a fused-ring or inserting acetylene units between the substituents and benzene. These are ascribable to changes in the charge-transfer structure by the π extension.

Missing-orbital analysis on hyperpolarizability β of organic molecules. Enhancement of the off-diagonal component βzxx using multiple substitutions

Abstract The first-order hyperpolarizability components, βzzz and βzxx, for C2v molecules (the z axis being the principal axis) are analyzed after simplified sum-over-states calculations. Compared with p-nitroaniline (PNA), βzxx is three times enhanced by x-extended π conjugation realized by a bulky substrate in 9-amino-10-nitroanthracene (ANA) and by multiple substitutions in 1,5-diamino-2,4-dinitrobenzene (DDB). While ANA shows βzzz unchanged because its z-directed charge transfer (CT) is similar to PNA, DDB has a β zzz 1 3 of PNA, which is reduced by two weak CTs introduced by two ortho-positioned donor-acceptor pairs on both sides of the z axis.

Theoretical study of the TiC molecule: clarification of the ground state

The electronic structure of the TiC molecule was examined using three types of multi-reference single- and double-excitation configuration interaction (MRSDCI) calculations with highly extended basis sets. Multi-reference coupled pair approximation (MRCPA) was applied after the MRSDCI calculations that included core—valence and core—core correlation in addition to the valence correlation (v-c-c CI). From the results of the most accurate calculation with MRCPA (v-c-c CPA) it was concluded that a 1Σ+ state is the ground state, despite previous calculations that suggested a 3Σ+ state with a 1Σ+ state lying only slightly above it. The 1Σ+ state is more highly correlated than the 3Σ+ state, and it was found that use of a size-consistent method is necessary to predict the relative stability accurately. The study evaluated the spectroscopic constants and considered the effect of the core (Ti 3p) correlation on these parameters. By taking the core correlation effect into account, the estimation of the dissociation energy (D e) was improved dramatically; D e obtained through v-c-c CPA was 4.457eV for the 1Σ+ ground state, which agrees well with the experimental value (the latest being 4.35 ± 0.31 eV).

Missing-orbital analysis of molecular hyperpolarizability β calculated by a simplified sum-over-states method. Enhancement of the off-diagonal component βzxx

Abstract The off-diagonal component of the first-order hyperpolarizability tensor βzxx of C2v molecules, e.g. substituted polyynes and benzenes, has been calculated by a simplified sum-over-states method. The missing-orbital analysis of the calcualted results reveals that excitations from a2 and b2 orbitals contribute cooperatively to βzxx, suggesting an insufficiency of the two-state model to describe βzxx. Increasing the number of occupied a2 orbitals enhances the magnitude of βzxx. For the C2v molecule with a2 orbitals widely extended in the x direction, βzxx can exceed βzzz, as found in 9-amino-10-cyanoanthracene having a βzxx about twice as large as βzzz.

Ab initio calculation of the electronic structures of the Φ3 ground and Φ5 excited states of CoH

The electronic structures and the spectroscopic constants of the electronic ground Φ3 and low-lying Φ5 electronic excited states of the CoH molecule were studied by multireference single and double excitation configuration interaction (MR-SDCI)+Davidson’s correction (Q) calculations and size-consistent multireference coupled pair approximation (MRCPA) calculations. Calculations were performed under C∞v symmetry using Slater-type basis functions. The electronic ground state was confirmed to be the Φ3 state. It was found that at least four reference configurations were needed to describe the ground Φ3 state correctly at the MR-SDCI+Q level, while the Φ5 state can be described well by one reference configuration, namely, the Hartree-Fock configuration. Larger dynamical electron correlation for the low-spin Φ3 state than that for the high-spin Φ5 state is discussed. Spectroscopic constants, i.e., equilibrium bond lengths (re), harmonic frequency (ωe), and excitation energy, obtained by the MR-SDCI+Q method sh...

HYPERPOLARIZABILITIES OF SI CLUSTERS : MODEL CALCULATIONS TO INTERPRET SECOND-HARMONIC GENERATION FROM SIO2/SI(111) INTERFACE

Abstract We have evaluated molecular hyperpolarizability β of Si clusters either with or without a dangling bond normal to Si(111) surface, and discussed the results in relation to the second-harmonic-generation (SHG) measurement from SiO 2 /Si(111) interface. The simplified sum-over-states calculation and missing-orbital analysis are extended to handle an open shell system, i.e. a dangling bond. In the presence of the dangling bond, β is caused by charge-transfers from the cluster interior to the dangling bond, while its absence by hydrogen termination greatly reduces β. This is consistent with the experiment that SHG is reduced by termination of interfacial Si atoms by annealing under hydrogen ambient.

Missing-orbital analysis of molecular hyperpolarizability β calculated by a simplified sum-over-states method: “multi-state” model for βzxx

Abstract Missing-orbital analysis is applied to the diagonal and off-diagonal components of the first-order hyperpolarizability tensor β evaluated by a simplified sum-over-states method. Various molecules assumed to have C2v symmetry are examined: benzene, pyridine-oxide and polyynes substituted with amino and either cyano or nitro groups. The missing-orbital analysis shows that the diagonal component βzzz (z-axis in the donor-to-acceptor direction) for most of the molecules is essentially dominated by only one strongly charge-transfer excited configuration, and is describable by the conventional two-state model. For the off-diagonal component βzxx, it is revealed that the excitations from a2 and b2 orbitals cooperatively make an important contribution. This indicates that, even for the molecules whose βzzz is described well by the two-state model, βzxx is necessarily modeled by a “multi-state” model consisting of the ground state and at least two excited configurations belonging to two different symmetries.

Hyperpolarizabilities βzzz and βzxx of π-extended molecules tetra-substituted by ortho-positioned donor–acceptor pairs as analyzed by homologous substitution model

Abstract Hyperpolarizability β of fused-ring molecules tetra-substituted by two ortho -positioned donor (D)–acceptor (A) were studied for three types of C 2v isomers, using simplified sum-over-states (SOS) calculation, missing-orbital analysis (MOA), and homologous substitution model. The model is comprised of two molecules, one di-substituted by two Ds, the other by two As at the sites homologous as a whole to tetra-substitution. Ortho 1-type with two D–A pairs at molecular x -edges showed larger β zxx than that of the model, exhibiting charge-transfer (CT), nevertheless all isomer types could show CT enhancement according to resonant structures. The substitution model successfully described qualitatively magnitudes and signs for β for all isomers.

Ab initio calculation of the electronic structures of the ∑7+ ground and A Π7 and a ∑5+ excited states of MnH

Electronic structures and molecular constants of the ground (7)Sigma(+) and low-lying A (7)Pi and a (5)Sigma(+) electronic excited states of the MnH molecule were studied by multireference single and double excitation configuration interaction (MR-SDCI) with Davidsons correction (+Q) calculations under exact C(infinity v) symmetry using Slater-type basis sets. To correctly describe the (7)Sigma(+) electronic ground state, X (7)Sigma(+), at the MR-SDCI+Q calculation, we employed a large number of reference configurations in terms of the state-averaged complete active space self-consistent field (CASSCF) orbitals, taking into account the contribution from the B (7)Sigma(+) excited state. The A (7)Pi and a (5)Sigma(+) states can well be described by the MR-SDCI wave functions based on the CASSCF orbitals obtained for the lowest state only. In the MR-SDCI+Q, calculations of the X (7)Sigma(+), A (7)Pi, and a (5)Sigma(+) states required 16, 7, and 17 reference configurations, respectively. Molecular constants, i.e., r(e) and omega(e) of these states and excitation energy from the X (7)Sigma(+) state, obtained at the MR-SDCI+Q level, showed a good agreement with experimental values. The small remaining differences may be accounted for by taking relativistic effects into account.