Masahiro Ehara

Variational calculations of fermion second-order reduced density matrices by semidefinite programming algorithm

The ground-state fermion second-order reduced density matrix (2-RDM) is determined variationally using itself as a basic variable. As necessary conditions of the N-representability, we used the positive semidefiniteness conditions, P, Q, and G conditions that are described in terms of the 2-RDM. The variational calculations are performed by using recently developed semidefinite programming algorithm (SDPA). The calculated energies of various closed- and open-shell atoms and molecules are excellent, overshooting only slightly the full-CI energies. There was no case where convergence was not achieved. The calculated properties also reproduce well the full-CI results.

Double-core-hole spectroscopy for chemical analysis with an intense X-ray femtosecond laser

Theory predicts that double-core-hole (DCH) spectroscopy can provide a new powerful means of differentiating between similar chemical systems with a sensitivity not hitherto possible. Although DCH ionization on a single site in molecules was recently measured with double- and single-photon absorption, double-core holes with single vacancies on two different sites, allowing unambiguous chemical analysis, have remained elusive. Here we report that direct observation of double-core holes with single vacancies on two different sites produced via sequential two-photon absorption, using short, intense X-ray pulses from the Linac Coherent Light Source free-electron laser and compare it with theoretical modeling. The observation of DCH states, which exhibit a unique signature, and agreement with theory proves the feasibility of the method. Our findings exploit the ultrashort pulse duration of the free-electron laser to eject two core electrons on a time scale comparable to that of Auger decay and demonstrate possible future X-ray control of physical inner-shell processes.

Electronic excitation spectra of furan and pyrrole: Revisited by the symmetry adapted cluster-configuration interaction method

Electronic excitation spectra of furan and pyrrole are reinvestigated by the symmetry-adapted cluster configuration-interaction method. The 47 and 46 lowest singlet and triplet electronic states are computed for furan and pyrrole, respectively. Two series (1a2 and 2b1) of low-lying Rydberg states and the valence π–π* excited states strongly influence each other in both furan and pyrrole. The present calculations give detailed and satisfactory theoretical assignments of the vacuum ultraviolet spectra and the electron energy-loss spectra of the two molecules. The similarities and differences in the electronic excitations between furan and pyrrole are discussed in detail. The accuracy and assignments of recent theoretical studies, i.e., complete active space second-order perturbation, multireference Moller–Plesset perturbation, second-order algebraic-diagrammatic construction, multireference double configuration interaction, and CC3, are compared.

Molecular double core-hole electron spectroscopy for chemical analysis

We explore the potential of double core hole electron spectroscopy for chemical analysis in terms of x-ray two-photon photoelectron spectroscopy. The creation of deep single and double core vacancies induces significant reorganization of valence electrons. The corresponding relaxation energies and the interatomic relaxation energies are evaluated by complete active space self-consistent field (CASSCF) calculations. We propose a method on how to experimentally extract these quantities by the measurement of single ionization potentials (IPs) and double core hole ionization potentials (DIPs). The influence of the chemical environment on these DIPs is also discussed for states with two holes at the same atomic site and states with two holes at two different atomic sites. Electron density difference between the ground and double core hole states clearly shows the relaxations accompanying the double core hole ionization. The effect is also compared to the sensitivity of single core hole IPs arising in single co...

Symmetry-adapted cluster and symmetry-adapted cluster-configuration interaction method in the polarizable continuum model: Theory of the solvent effect on the electronic excitation of molecules in solution

In this paper we present the theory and implementation of the symmetry-adapted cluster (SAC) and symmetry-adapted cluster-configuration interaction (SAC-CI) method, including the solvent effect, using the polarizable continuum model (PCM). The PCM and SAC/SAC-CI were consistently combined in terms of the energy functional formalism. The excitation energies were calculated by means of the state-specific approach, the advantage of which over the linear-response approach has been shown. The single-point energy calculation and its analytical energy derivatives are presented and implemented, where the free-energy and its derivatives are evaluated because of the presence of solute-solvent interactions. We have applied this method to s-trans-acrolein and metylenecyclopropene of their electronic excitation in solution. The molecular geometries in the ground and excited states were optimized in vacuum and in solution, and both the vertical and adiabatic excitations were studied. The PCM-SAC/SAC-CI reproduced the known trend of the solvent effect on the vertical excitation energies but the shift values were underestimated. The excited state geometry in planar and nonplanar conformations was investigated. The importance of using state-specific methods was shown for the solvent effect on the optimized geometry in the excited state. The mechanism of the solvent effect is discussed in terms of the Mulliken charges and electronic dipole moment.

Electronic Excitations of the Green Fluorescent Protein Chromophore in Its Protonation States: SAC/SAC-CI Study

Two ground‐state protonation forms causing different absorption peaks of the green fluorescent protein chromophore were investigated by the quantum mechanical SAC/SAC‐CI method with regard to the excitation energy, fluorescence energy, and ground‐state stability. The environmental effect was taken into account by a continuum spherical cavity model. The first excited state, HOMO‐LUMO excitation, has the largest transition moment and thus is thought to be the source of the absorption. The neutral and anionic forms were assigned to the protonation states for the experimental A‐ and B‐forms, respectively. The present results support the previous experimental observations.

Density matrix variational theory: Application to the potential energy surfaces and strongly correlated systems

The density matrix variational theory (DMVT) algorithm developed previously [J. Chem. Phys. 114, 8282 (2001)] was utilized for calculations of the potential energy surfaces of molecules, H4, H2O, NH3, BH3, CO, N2, C2, and Be2. The DMVT(PQG), using the P, Q, and G conditions as subsidiary condition, reproduced the full-CI curves very accurately even up to the dissociation limit. The method described well the quasidegenerate states and the strongly correlated systems. On the other hand, the DMVT(PQ) was not satisfactory especially in the dissociation limit and its potential curves were always repulsive. The size consistency of the method was discussed and the G condition was found to be essential for the correct behavior of the potential curve. Further, we also examined the Weinhold–Wilson inequalities for the resultant 2-RDM of DMVT(PQG) calculations. Two linear inequalities were violated when the results were less accurate, suggesting that this inequality may provide a useful N-representability condition ...

Outer- and inner-valence ionization spectra of N2 and CO:: SAC-CI (general-R) compared with full-CI spectra

Abstract The SAC-CI (symmetry-adapted-cluster configuration-interaction) (general-R) method describes the ionization and shake-up spectra of N 2 and CO in almost complete agreement with the full-CI results, though the computational labour of the former is much smaller that that of the latter. The SAC-CI (general-R) method is accurate for both valence and inner-valence regions of ionization spectra, while the SAC-CI (SD-R) method is good for the outer-valence region, but not always so for the shake-up region.

Multiconfiguration time-dependent Hartree (MCTDH) study on rotational and diffractive inelastic molecule-surface scattering

The multiconfiguration time‐dependent Hartree (MCTDH) method is applied to rotational and diffractive inelastic molecule‐corrugated surface scattering. The molecule is treated as a rigid rotor, hence there are five degrees of freedom included in the calculation. The model systems H2/rectangular lattice and N2/LiF (001) are investigated for scattering with normal incidence. The performance and reliability of the MCTDH method is critically examined with respect to the structure of the MCTDH wave function and the choice of the basis set representation. The MCTDH reproduces the fine details of the state‐to‐state transition probabilities calculated by the numerically exact close‐coupled wave packet (CCWP) method. We show that it is useful to represent two of the internal degrees of freedom by one set of single‐particle functions when these degrees are strongly coupled, or when their MCTDH‐contraction efficiency is low.

Nonequilibrium solvation for vertical photoemission and photoabsorption processes using the symmetry-adapted cluster-configuration interaction method in the polarizable continuum model

In this paper, we present the theory and implementation of a nonequilibrium solvation model for the symmetry-adapted cluster (SAC) and symmetry-adapted cluster-configuration interaction (SAC-CI) method in the polarizable continuum model. For nonequilibrium solvation, we adopted the Pekar partition scheme in which solvent charges are divided into dynamical and inertial components. With this nonequilibrium solvation scheme, a vertical transition from an initial state to a final state may be described as follows: the initial state is described by equilibrium solvation, while in the final state, the inertial component remains in the solvation for the initial state; the dynamical component will be calculated self-consistently for the final state. The present method was applied to the vertical photoemission and absorption of s-trans acrolein and methylenecyclopropene. The effect of nonequilibrium solvation was significant for a polar solvent.