Yukio Kawashima

A polarizable mixed Hamiltonian model of electronic structure for micro-solvated excited states. I. Energy and gradients formulation and application to formaldehyde (1A2)

We describe an efficient implementation of a polarizable mixed Hamiltonian model of electronic structure that combines Hartree–Fock, Kohn–Sham, or multiconfiguration quantum-chemical wave functions with a polarizable and flexible molecular mechanics potential of water, and that is applicable to micro-solvated electronic excited states. We adopt a direct algorithm for the calculation of the polarization response of the solvent subsystem. The strategy facilitates the calculation of the energy of the system and of the forces with respect to the solute coordinates and the solvent coordinates, including for excited states. This capability opens the way to the determination of optimized, transition structures, force constants, and intrinsic reaction pathways for the solute–solvent system, and to molecular dynamics calculations to account for finite temperature effects. As an illustration we characterize the structure and energy of micro-solvated formaldehyde H2CO in its ground state and in its 1(π*←n) excited s...

Theoretical study of the π → π∗ excited states of linear polyene radical cations and dications

Abstract Multireference Moller-Plesset theory is applied to the study of the valence π → π ∗ excited states of radical cations and dications of butadiene, hexatriene, octatetraene and decapentaene. The present theory satisfactorily describes the low-lying excited states of cations within an error of 0.1 eV. Theory confirms the general tendency observed in carotenoids that the first transition of the dications of polyenes is at a higher energy than the intense transition of the radical cations and at a lower energy than the first allowed transition of the neutral species.

Monte Carlo microsolvation simulations for excited states using a mixed-Hamiltonian model with polarizable and vibrating waters: Applications to the blueshift of the H2CO 1(π*←n) excitation

The previously formulated quantum mechanical molecular mechanical (QM/MM) model applicable to the microsolvated solute excited state, the QM/MM-pol-vib/CAV model, has been combined with a Monte Carlo averaging scheme to derive the averaged properties of the solvated solutes. The methodology was applied to the electronic 1(π*←n) excitation of formaldehyde in water. We first performed Monte Carlo MM/MM calculations to generate the water configurations. Then, we chose 400 configurations for the QM/MM excitation energy calculations. Finally, we carried out complete active space self-consistent field calculations to derive the average excitation energy. Several different sizes of water clusters with 23, 54, and 108 water molecules were used. The first solvent shell of the clusters was found to be well structured. We also calculated the shift of the vertical excitation energies and of the dipole moments resulting from microsolvation. The calculated blueshift of the vertical excitation energies using a nonpolari...

Assessment of free energy expressions in RISM integral equation theory: theoretical prediction of partition coefficients revisited

We assess the performance of free energy expressions so far available in the reference interaction site model (RISM) integral equation theory. Free energies of solvation in aqueous and chloroform solutions along with the partition coefficients of them are calculated for 16 organic molecules. Static polarity effects are included using hybrid RISM and Hartree–Fock methods. Our best estimates are obtained from the expression of the distributed partial wave expansion that leads to the standard deviations less than 1.3 kcal mol−1 and 1.1 in the solvation free energies and partition coefficients, respectively.

A polarizable mixed Hamiltonian model of electronic structure for solvated excited states. II. Application to the blue shift of the H2CO 1(π*←n) excitation in water

We illustrate an application of a polarizable mixed Hamiltonian model of solvation developed in the companion Paper I [J. Chem. Phys. 117, 1242 (2002)] and describe the structure of electronically excited formaldehyde in water. We used Hartree-Fock and multiconfiguration wave functions together with the tip3p, pol1, and pol2 interaction potentials combined with the Bartlett–Shavitt vibrational potential for water. We calculated the structure of H2CO (1A1, 3A2, and 1A2) micro-solvated with 1 or 2 water molecules and we mimicked the aqueous environment with up to 81 waters with equilibrium solute–solvent configurations. We calculated the vertical and adiabatic excitations energies. The vertical absorption energy shows a blue shift between ∼1000 and ∼2500u2009cm−1 due to solvation, that is in fact already present in the micro-solvated systems and increases with the degree of solvation. The dipole moments of the ground and excited states show a marked increase with the degree of solvation. The polarizable charact...

Theoretical investigation of the molecular and electronic structures and excitation spectra of iron phthalocyanine and its derivatives, FePc and FePcLn (L = Py, CN−; n = 1, 2)

The effects of axial ligands on the ground-state geometries, electronic structures and the characteristic optical properties of iron phthalocyanine and its derivatives, FePc and FePcL(n) (L = pyridine (Py) and cyanide (CN(-)); n = 1, 2), were investigated using the density functional theory (DFT) method. The geometries of FePc with a triplet spin state and of FePc(Py), FePc(Py)(2), FePc(CN(-)) and FePc(CN(-))(2) with singlet spin states were optimized under D(4h), C(2v), D(2h), C(4v), and D(4h) molecular symmetries, respectively. The highest occupied molecular orbitals (HOMOs) of FePc, FePc(Py), FePc(Py)(2), and FePc(CN(-)) are pi-type orbitals, which have no contribution from the p(z) atomic orbitals of all nitrogen atoms, whereas the HOMO of FePc(CN(-))(2) is the 7e(g) orbital, which has contributions from the d(xz) and the d(yz) orbitals of the Fe atom mixing with the pi-orbitals of the axial CN(-) ligands. The time-dependent (TD) DFT method gives many optically allowed excitations for FePc, FePc(Py), FePc(Py)(2), FePc(CN(-)), and FePc(CN(-))(2) in the UV-VIS region. Our calculated bands corresponded well with the experimental results. In FePc(Py)(2), the metal-ligand charge transfer (MLCT) transitions from the metal d to the axial-ligand pi*-type orbitals contributed to the B band region. In FePc(CN(-))(2), the MLCT transitions from the metal d to the Pc-ring pi*-type orbitals contributed mainly to the first B band region, but those from the metal d to the axial-ligand pi*-type orbitals did not appear in the energy regions of the Q and B bands. Thus, the axial ligands caused a spectral change in FePc through orbital mixing.

Theoretical investigation of the molecular, electronic structures and vibrational spectra of a series of first transition metal phthalocyanines by Z. Liu et al.

A recent paper by Lui et al. [Z. Liu, X. Zhang, Y. Zhang, J. Jiang, Spectrochim. Acta A 67 (2007) 1232] reported on the theoretical investigations of the fully optimized geometries and electronic structures of iron (II) phthalocyanine (FePc) with the singlet spin state carried out with the restricted density functional theory (DFT) method, where the B3LYP functional was adopted for the exchange-correlation term; however, the triplet spin state was experimentally reported, and we also obtained the triplet spin state by the unrestricted DFT calculations.

Theoretical study on the molecular structures of X-, α-, and β-types of lithium phthalocyanine dimer

We report here the results from theoretical calculations of the potential energy curves, the geometry optimizations, and the electronic structures for three dimers of lithium phthalocyanine (LiPc) by using three types of functional systems: PBE1PBE, B3LYP, and M06. The results were discussed in comparison with those obtained for the dimers of magnesium phthalocyanine (MgPc). The long‐range dispersive interactions were considered in part using these functional systems in the increasing order of PBE1PBE, B3LYP, and M06. The mechanism whereby the dispersive interactions affect the geometric and electronic structures of the LiPc and MgPc dimers is discussed. The calculated results provide insight into the computational methods for both open‐ and closed‐shell metal phthalocyanine (MPc) dimers: Although the PBE1PBE and B3LYP functional systems cannot evaluate a weak dispersion interaction appropriately, the M06 functional can estimate a weak dispersion interaction well in both open‐ and closed‐shell MPc dimers. Basis set superposition error (BSSE) corrections play an important role for the quantitative analysis; however, the calculation results without BSSE corrections may be sufficient for the qualitative discussion on the properties of these dimers such as geometries, stabilities, electronic structures, and so on.

Low-lying excited states of C120 and C151: a multireference perturbation theory study.

Excited states of two 7-aminocoumarin derivatives, coumarin 120 (7-amino-4-methylcoumarin) and coumarin 151 (7-amino-4-trifluoromethylcoumarin), were investigated using generalized multiconfigurational quasidegenerate perturbation theory (GMC-QDPT), multiconfigurational quasidegenerate perturbation theory (MC-QDPT) and time-dependent density functional theory (TDDFT) with the B3LYP and CAM-B3LYP functionals. The absorption and fluorescence spectra of C120 and C151 were calculated. We elucidated the characters of the low-lying states of C120 and C151. The absorption spectra calculated with GMC-QDPT and TDDFT B3LYP agreed well with the experimental data, while for the fluorescence spectra, the TDDFT calculations overestimated the fluorescence spectra compared to GMC-QDPT calculations. Utilizing active spaces with large numbers of electrons and orbitals for reference functions, GMC-QDPT showed a better performance than MC-QDPT with a complete active space self-consistent field (CASSCF) reference of active space with smaller number of electrons and orbitals. In our gas phase calculation, we found that the optimized structures for the first excited states have a planar amino group with a CN single bond, while the amino group is pyramidal in the ground state.

Theoretical and experimental investigation on the electronic properties of the shuttlecock shaped and the double-decker structured metal phthalocyanines, MPc and M(Pc)2 (M = Sn and Pb)

The molecular geometries, electronic structures, and excitation energies of tin and lead phthalocyanine compounds, SnPc, PbPc, Sn(Pc)(2), and Pb(Pc)(2), were investigated using the B3LYP method within a framework of density functional theory (DFT). The geometries of SnPc, PbPc, Sn(Pc)(2), and Pb(Pc)(2) were optimized under C(4v), C(4v), D(4d), and D(4d) molecular symmetries, respectively. The excitation energies of these molecules were computed by the time-dependent DFT (TD-DFT) method. The calculated results for the excited states of three compounds other than the unknown Pb(Pc)(2) corresponded well with the experimental results of electronic absorption spectroscopy. The non-planar C(4v) molecular structure of SnPc and PbPc influences especially on the orbital energy of the HOMO-1 through mixing of the s-type atomic orbital of the central metal atom to the π system of the Pc ring in an anti-bonding way; however, the HOMO and the LUMO have little effect of the deviation from the planar structure because they have no contribution from the atomic orbital of the central metal. This orbital mixing pushes up the orbital energy of the HOMO-1, and reduces the energy of the metal-to-ligand charge transfer band of SnPc and PbPc. The calculated results also reproduced well the excitation profile of Sn(Pc)(2), which was quite different from that of SnPc. The strong interactions between the π-type orbitals of two Pc moieties altered the electronic structure resulting in the characteristic excitation profile of Sn(Pc)(2). In addition, this caused a reduction of about 0.8 eV in the ionization potential as compared to usual MPcs including SnPc, which was consistent with the experimental results.