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Relative stability between manganese hydroxide (H2O)2(OH)4Mn(IV) OH (1) and manganese oxo (H2O)3(OH)3Mn(IV) O (2) species were investigated by coupled cluster (CC) SD and SD(T), DMRG CASCI, CASSCF, CASPT2 and CASDFT methods. The DMRG CASCI and DMRG CASSCF based on thirteen active orbitals and thirteen active electrons {13, 13} CAS space indicted the greater stability of 2 than 1. On the other hand, the relative stability between 1 and 2 was reversed by UCC SD, DLPNO-UCC SD, CASPT2 and CAS-DFT, indicating an important role of dynamical electron correlation corrections. Implications of present results are discussed to elucidate scope and applicability of hybrid DFT (HDFT) methods for 1 and 2.

The reaction mechanism of the O2 formation in the S4 state of the oxygen-evolving complex of photosystem II was clarified at the quantum mechanics/molecular mechanics (QM/MM) level. After the Yz (Y161) oxidation and the following proton transfer in the S3 state, five reaction steps are required to produce the molecular dioxygen. The highest barrier step is the first proton transfer reaction (0 → 1). The following reactions involving electron transfers were precisely analyzed in terms of their energies, structures and spin densities. We found that the one-electron transfer from the Mn4Ca cluster to Y161 triggers the O–O sigma bond formation.

Conventional quantum chemical and solid-state physical approaches include several problems to accurately calculate solid-state nuclear magnetic resonance (NMR) properties. We propose a reliable computational scheme for solid-state NMR chemical shifts using an extrapolation scheme that retains the advantages of these approaches but reduces their disadvantages. Our scheme can satisfactorily yield solid-state NMR magnetic shielding constants. The estimated values have only a small dependence on the low-level density functional theory calculation with the extrapolation scheme. Thus, our approach is efficient because the rough calculation can be performed in the extrapolation scheme.

In this letter we present results of study of weak C H⋯O C hydrogen bonds of crystalline poly-(R)-3-hydroxybutyrate (PHB) by using Born-Oppenheimer molecular dynamics. The polymeric structure and IR spectra of PHB result from the presence of the weak hydrogen bonds. We applied the post-molecular dynamics analysis to consider a C O motion as indirectly involved in the hydrogen bonds. Quantization of the nuclear motion of the oxygens was done to perform detailed analysis of the strength and properties of the C O bands involved in the weak hydrogen bonds. We have also shown the dynamic character of the weak hydrogen bond interactions.

Large-scale QM/MM calculations including hydrogen-bonding networks in the oxygen evolving complex (OEC) of photosystem II (PSII) were performed to elucidate the geometric structures of the CaMn 4 O 5 cluster in the key catalytic states (S i ( i = 0–3)). The optimized Mn–Mn, Ca–Mn and Mn–O distances by the large-scale QM/MM starting from the high-resolution XRD structure were consistent with those of the EXAFS experiments in the dark stable S 1 state by the Berkeley and Berlin groups. The optimized geometrical parameters for other S i ( i = 0, 2, 3) states were also consistent with those of EXAFS, indicating the importance of the large-scale QM/MM calculations for the PSII-OEC.

We study spin-forbidden transitions of Os polypyridyl sensitizers by two-component relativistic time-dependent density functional theory with the spin–orbit interaction based on Tamm–Dancoff approximation. The absorption spectra, including spin-forbidden-transition peaks, for the Os complexes are reasonably reproduced in comparison with the experimental ones. The extension of the conjugated lengths in the Os complexes is investigated and found to be effective to enhance photo absorption for spin-allowed transitions as well as spin-forbidden ones. This study provides fruitful information for a design of new dyes in terms of conjugation lengths.

A Gaussian-based range-separation approach is applied to the Hartree–Fock exchange interaction and the second-order perturbation theory, comparing the results with those provided through the erfc short-range potential approach. The Gaussian short-range potential's behavior resembles more that of the bare 1/r potential than that of the erfc short-range potential around the origin. Thus, the Gaussian-based range-separation of the exchange term agrees better with the ordinary HF method and the Moller–Plesset perturbation theory.

Full geometry optimizations of ([CaMn4O4(CH3COO)8(py)(CH3COOH)2], (py: pyridine) (1)) were performed at the UB3LYP theoretical level. 1 is a theoretical model for the synthetic model ([CaMn4O4(ButCOO)8(py)(ButCOOH)2], (But: t-butyl) (2)) which closely mimicks the native oxygen evolving complex (OEC) in photosystem II. It was shown that the X-ray structure of 2 was well reproduced by 1 in the (Mn1(III), Mn2(IV), Mn3(IV), Mn4(III)) valence state with the unprotonated O5 (O5 = O2−), and two different valence states were obtained in the one-electron oxidized state. Importance of the Jahn–Teller effect of the Mn(III) site for the structural deformations was presented.

Domain-based local pair natural orbital (DLPNO) coupled cluster single and double (CCSD) with triple perturbation (T) correction methods were applied for fourteen different S2 structures of the CaMn4O5 cluster in oxygen evolving complex (OEC) of photosystem II (PSII). The DLPNO-CCSD(T0) calculations elucidated that the right (R)-opened S2aYZ structure (a = O2− at the O(5) site, Y = W2 and Z = W1) with the low spin (LS) (S = 1/2, g = 2) state and two left (L)-opened S2aYZ structures with the high spin (HS) (S = 5/2, g = 4; g > 4) state were nearly degenerated in energy, supporting previous one LS-two HS model for the S2 state in compatible with recent EXAFS and EPR results.

Domain-based local pair natural orbital (DLPNO) coupled cluster single and double (CCSD) with triple perturbation (T) correction methods were applied for six different S1 structures of oxygen evolving complex (OEC) of photosystem II (PSII), showing that right-opened three S1 structures were nearly degenerated in energy. The DLPNO- CCSD(T0) calculations support proposals of the multi-intermediate models for the S1 state in accord with the EPR, other experimental and DFT computational results.

A Gaussian-based cutoff scheme in the dielectric-dependent Hartree–Fock (HF) exchange potential under periodic boundary conditions is discussed. The scheme is applied to HF and hybrid density functional theory methods. For comparison, we examine short-range potentials based on the complementary error function. To investigate the behaviors of these short-range exchange potentials, we study several polymers, such as polyethylene and polytetrafluoroethylene.

Spin-forbidden transitions of metal polypyridyl sensitizers are studied by the two-component relativistic time-dependent density functional theory with spin–orbit interaction based on Tamm–Dancoff approximation. The spin-forbidden transitions for a phosphine-coordinated Ru(II), DX1, as well as the modified DX1 complexes whose Ru is replaced with Fe and Os, are calculated. The role of the central metals in spin-forbidden transitions is discussed toward the exploration for new efficient sensitizers.

Interaction energies, geometry and vibrational frequencies of the gas-phase HF-dimethyl ether complex were obtained using quantum-chemical methods. Equilibrium and vibrationally averaged geometries, harmonic and anharmonic wavenumbers of the complex were calculated using second-order perturbation theory procedures with B3LYP, B2PLYP-D and MP2 methods with 6-311++G(2df, 2pd) basis set. Quantum-mechanical model describing anharmonic-type vibrational couplings within hydrogen bond was used to explain broadening, fine structure and temperature dependence of the F H stretching IR absorption bands as effect of hydrogen bond formation. Simulations of the rovibrational structure of the F H stretching bands were performed for different temperatures. The results were compared with experimental spectra.

For the calculation of the spin–orbit (SO) contribution to zero-field splitting (ZFS) tensor, we derive the ZFS formula based on the two-component relativistic second-order Moller–Plesset perturbation theory with the second-order Douglas–Kroll–Hess (DKH2) Hamiltonian from the ZFS formula described by sum-over-states form. The present ZFS formula is obtained also from the ZFS formula (with a prefactor) based on the coupled-perturbed spin–orbit coupling (CP-SOC) method of Neese. For several organic magnetic molecules, the calculated ZFS parameters (DSO and ESO) by the present ZFS formula almost agree with those by the CASSCF/MRMP2 method.

Novel zero-field splitting (ZFS) formula is developed to calculate the spin–orbit contribution ( D SO ) to the ZFS tensor by using finite-perturbation theory, i.e., two-component self-consistent-field procedures with second-order Douglas–Kroll–Hess Hamiltonian. The ZFS formula is extended to second-order generalized unrestricted Moller–Plesset perturbation theory. For triplet diatomic molecules, several fundamental contributions to the D SO tensor are investigated. The electron-correlation effects were relatively large (more than 23%) and were very significant (more than 56%) especially for SeS, Se 2 , and Te 2 .

An efficient approach to the fully relativistic density-functional theory (DFT) is proposed to accelerate Dirac–Kohn–Sham calculation that uses high-quality basis sets and hybrid exchange–correlation functional. The dual-level approach proposed by Nakajima and Hirao underlies the present method, estimating high-level four-component DFT energy perturbatively from reference density matrix, which is determined by a relatively inexpensive self-consistent calculation using low-quality basis sets and low-cost functional. A further approximation based on Infinite-Order Two-Component relativistic Hamiltonian is incorporated into the low-level treatment. Accuracy and efficiency were examined by benchmark calculation of spectroscopic values for MH, M 2 (M = Cu, Ag, and Au), and AtH.

We compare the absorption/emission energies of three heteroaromatic chromophores, indoles, benzofurazans and coumarins, both experimentally and theoretically. First we used TDDFT and SAC-CI methods to calculate S0 → S1 vertical excitation energies corresponding to the absorptions. The excitation energies obtained by the SAC-CI method were superior to those obtained by the TDDFT method, as well as being consistent with those experimentally obtained. We thus applied the SAC-CI method to estimate the emission energies of these chromophores on the basis of the CIS- or TDDFT-optimized excited-state structures. We found a good and consistent agreement of the CIS-structure-based values with the experimental values, whereas the TDDFT-structure based values showed less good agreement.

We propose an implementation of the large-scale MP2 approach obtained by combining the advantages of several approximate MP2 approaches. Our method is based on the local Laplace-transform MP2 method with the resolution of the identity approximation, which we denote the RILL-MP2 method. Applications of the RILL-MP2 method to linear glycine polypeptide and Se(CuPH3)2 molecules show that this approach is more efficient than the traditional or other approximate approaches without invoking loss of accuracy as the system size increases.

We have developed the adaptive density partitioning technique (ADPT) in the auxiliary plane wave method, in which a part of the density is expanded to plane waves, for the fast evaluation of Coulomb matrix. Our partitioning is based on the error estimations and allows us to control the accuracy and efficiency. Moreover, we can drastically reduce the core Gaussian products that are left in Gaussian representation (its analytical integrals is the bottleneck in this method). For the taxol molecule with 6-31G** basis, the core Gaussian products accounted only for 5% in submicrohartree error.

An ab initio direct molecular dynamics study of the reaction of CH 3 + with benzene has been performed and the mechanism of reaction examined. Ab initio energy and gradient evaluations were done at the QCISD/6-31+G** and MP2/6-31+G** levels. The primary products of reaction were several isomeric forms of arenium ion (σ complex). The reaction proceeds through a single channel, a direct barrierless insertion of a methyl cation into benzene to form a σ complex. The direct insertion mechanism supports a recent quantum chemical study but differs from that posited in earlier experimental and theoretical studies of the reaction, which have assumed formation of a stable π complex. The molecular dynamics simulation shows that product arenium ions are internally energetic enough for a hydrogen to shift about the benzenium ring to form several isomers.

An efficient integral transformation program based on the four-component spinors resulting from the Dirac–Hartree–Fock (DHF) method is implemented in the R el4d program. By adopting generally contracted spherical harmonic Gaussian-type spinors, the small-component basis functions are almost half as many as the basis expansion with the decoupled scalar spin orbitals. This advantage is exploited to enhance the efficiency in the integral transformation. The present integral transformation program is 4–8 times faster than the pioneering programs of M olfdir and D irac . As an illustrative example, the CCSD and CCSD(T) methods are successfully applied to the ground state of thallium hydride.

An ab initio direct molecular dynamics study of the fragmentation of the unstable, neutral F(H2O) complex has been performed. A photodetachment experiment of the stable F−(H2O) anion complex produces F(H2O) in the vicinity of the transition-state region of the hydrogen abstraction reaction, F+H2O→FH+OH. Ab initio energy and gradient evaluations in the direct molecular dynamics simulation were done at the QCISD/6-311+G** level of theory. The product vibrational and rotational states were computed and the mechanism of the reaction examined. The primary products of reaction are vibrationally excited HF and rotationally warm but vibrationally cold (v″=0) OH. The reaction proceeds through three channels. In order of the frequency of occurrence, these are: (1) direct abstraction of a hydrogen atom by F; (2) dissociation into F+H2O; and (3) direct abstraction of a hydrogen atom by F with subsequent formation of a weakly bound FH–OH complex.

An ab initio model potential (AIMP) has been developed for the lanthanide series from Ce to Lu. The corresponding (14s10p9d8f) valence basis sets were optimized by means of the minimization of the valence SCF total energies. The relativistic effect was considered with the scalar relativistic third-order Douglas–Kroll approximation. The applicability of the present AIMP, and the valence basis sets, was tested for the lanthanide atoms, and a monoxide, CeO. Both the atomic and molecular AIMP calculations showed excellent agreement with all-electron calculations. The present AIMP scheme has proved to work well in the calculations of whole series of the lanthanides.

An analytic gradient technique for the relativistic elimination of small components (RESCs) approach has been successfully derived and implemented. An internal uncontraction scheme has been added to both energy and gradient, thus improving the resolution of the identity quality. The gradient technique is a full analytic derivative of the energy expression, including the resolution of the identity. A comparison to other similar relativistic methods has been performed on the following molecules: W(CO)6,Os(CO)5,Pt(CO)4 and good agreement to other methods is achieved, within the limitations of the basis set and electron correlation level (MP2).

The recently proposed third-order Douglas–Kroll method (DK3) is applied to superheavy element 112, the hydride of 112, and its ions. The results are compared to the second-order DK (DK2) results. The effect of the third-order scalar relativistic corrections with the DK3 Hamiltonian is found to be relatively small for the valence-shell properties of element 112, (1 1 2)H, and its ions although DK3 represents a significant improvement over DK2 for the inner core shells.

The relativistic scheme by the elimination of small components (RESC) of the four-component Dirac equation proposed previously has been incorporated into density functional theory (DFT). RESC–DFT results in a computationally efficient and numerically stable two-component Kohn–Sham formalism, suited for molecular applications. Illustrative calculations for AgH, AuH, AgCl, and AuCl have been performed employing various exchange-correlation functionals. A good agreement with experiment is obtained.

A new relativistic theory has been proposed by the elimination of small components of the Dirac equation. It is variationally stable and can easily be incorporated into any electronic structure theory. The present formalism is tested in standard problems of Ag and Au atoms and their hydrides at various levels of theory including single- and multi-reference-based methods. Numerical results show that good accuracy can be obtained.

The second-order perturbative approximation to the SAC (symmetry-adapted cluster)/SAC-CI (configuration interaction) method is proposed. It is used in various studies of electronic structures and spectroscopic properties of large molecules in ground, excited (singlet and triplet), ionized, and electron-attached states. The performance and the reliability of the proposed method are investigated by applications to several molecules in these electronic states.

Four-component relativistic theory of the magnetic shielding constant is presented, based on the matrix Dirac–Fock finite perturbation method and implemented for numerical calculations with the MOLFDIR program. In contrast to the non-relativistic and quasi-relativistic formalisms, the shielding constant is written as a single term. Our formulation avoids explicit use of the positron states, in contrast to the conventional sum-over-states formalism. The magnetic shielding constants of the noble gas atoms, He through Xe, and those of H2, HF and HCl are calculated and compared with values obtained in non-relativistic calculations.

The method of calculating the analytical energy gradients for the ground, excited, ionized and electron-attached states . . calculated by the SAC symmetry adapted cluster rSAC-CI configuration interaction method is formulated and imple- mented. It is adapted with the configuration selection procedure used in the SACrSAC-CI method. The performance of the method is investigated for the Li and CO molecules. q 1997 Elsevier Science B.V. 2

The 93 Nb and 47 Ti NMR chemical shifts of niobium hexahalides and titanium tetrahalides are studied theoretically by the ab initio UHF/finite perturbation method including the spin-orbit (SO) interaction. The calculated chemical shifts agree well with experiment for both the Nb and Ti compounds. In contrast to the halides of main-group elements studied previously, the SO effect is generally small for early transition metal halides. The origin of the chemical shifts lies in the d-orbital contribution of the paramagnetic term and is due to the d-d ∗ excitation mechanism. Soft d-orbitals adsorb the SO effect, leaving only a small net spin-orbit effect. The chemical shift shows a monotonic downfield shift as the halogen ligand becomes heavier (inverse halogen dependence), in contrast to the normal halogen dependence observed for the halides of main-group elements. It is expected that such a result is common to other transition metal halides in which the transition metal atom has an open d subshell.

The 29Si NMR chemical shifts of silane, SiH4, and silicon tetrahalides, SiX4 (X = F, Cl, Br and I) and SiXI3 (X = Cl and Br), are calculated by the ab initio unrestricted Hartree-Fock/finite perturbation method including the spin-orbit (SO) interaction proposed previously. The SO effect is included through the effective core potentials for the halogens. The chemical shifts calculated with the SO effects show good agreement with experiment for all the compounds studied. The SO effects of the halogen ligands, especially of bromine and iodine, are large and move the chemical shift to higher magnetic field. The inverse halogen dependence on the substitution of F by Cl is derived from the paramagnetic term, but the normal halogen dependence on the substitution from Cl to I is caused mainly by the SO effect.