State-interaction pair-density functional theory.

Chemical relaxation phenomena, including photochemistry and electron transfer processes, form a vigorous area of research in which nonadiabatic dynamics plays a fundamental role. However, for electronic systems with spin degrees of freedom, there are few if any applicable and practical quasiclassical methods. Here, we show that for nonadiabatic dynamics with two electronic states and a complex-valued Hamiltonian that does not obey time-reversal symmetry (as relevant to many coupled nuclear-electronic-spin systems), the optimal semiclassical approach is to generalize Tully's surface hopping dynamics from coordinate space to phase space. In order to generate the relevant phase-space adiabatic surfaces, one isolates a proper set of diabats, applies a phase gauge transformation, and then diagonalizes the total Hamiltonian (which is now parameterized by both R and P). The resulting algorithm is simple and valid in both the adiabatic and nonadiabatic limits, incorporating all Berry curvature effects. Most importantly, the resulting algorithm allows for the study of semiclassical nonadiabatic dynamics in the presence of spin-orbit coupling and/or external magnetic fields. One expects many simulations to follow as far as modeling cutting-edge experiments with entangled nuclear, electronic, and spin degrees of freedom, e.g., experiments displaying chiral-induced spin selectivity.

Multi-configuration pair-density functional theory (MC-PDFT) has previously been applied successfully to carry out ground-state and excited-state calculations. However, because they include no interaction between electronic states, MC-PDFT calculations in which each state's PDFT energy is calculated separately can give an unphysical double crossing of potential energy surfaces (PESs) in a region near a conical intersection. We have recently proposed state-interaction pair-density functional theory (SI-PDFT) to treat nearly degenerate states by creating a set of intermediate states with state interaction; although this method is successful, it is inconvenient because two SCF calculations and two sets of orbitals are required and because it puts the ground state on an unequal footing with the excited states. Here we propose two new methods, called extended-multi-state-PDFT (XMS-PDFT) and variational-multi-state-PDFT (VMS-PDFT), that generate the intermediate states in a balanced way with a single set of orbitals. The former uses the intermediate states proposed by Granovsky for extended multi-configuration quasi-degenerate perturbation theory (XMC-QDPT); the latter obtains the intermediate states by maximizing the sum of the MC-PDFT energies for the intermediate states. We also propose a Fourier series expansion to make the variational optimizations of the VMS-PDFT method convenient, and we implement this method (FMS-PDFT) both for conventional configuration-interaction solvers and for density-matrix-renormalization-group solvers. The new methods are tested for eight systems, exhibiting avoided crossings among two to six states. The FMS-PDFT method is successful for all cases for which it has been tested (all cases in this paper except O3 for which it was not tested), and XMS-PDFT is successful for all eight cases except the mixed-valence case. Since both XMS-PDFT and VMS-PDFT are less expensive than XMS-CASPT2, they will allow well-correlated calculations on much larger systems for which perturbation theory is unaffordable.

Trajectory surface hopping (TSH) methods have been widely used for the study of nonadiabatic molecular dynamics. In the present work, the accuracy of two TSH algorithms, Tully's fewest switching algorithm and an algorithm based on the Landau-Zener formula, has been critically evaluated in comparison with exact nonadiabatic quantum dynamics calculations for a model of the photoinduced hydrogen-atom dissociation reaction in phenol. The model consists of three electronic states (S0, 1ππ*, 1πσ*) and two nuclear degrees of freedom (the OH stretching coordinate and CCOH dihedral angle) and displays two successive conical intersections (1ππ*/1πσ* and 1πσ*/S0). Considering instantaneous photoexcitation from different vibrational levels of the S0 state to the 1ππ* state, we examined the time-dependent electronic population dynamics as well as the branching ratio of the two dissociation channels. The results of fully converged trajectory calculations are compared with the results of exact quantum wave-packet calculations. It is found that both TSH algorithms describe the dynamics at the 1πσ*/S0 conical intersection, which is accessed with high excess energy, with good accuracy. The 1ππ*/1πσ* conical intersection, on the other hand, is accessed with little excess energy so tunneling effects as well as wave-packet interference effects which cannot be reproduced with classical trajectory calculations become relevant. Overall, the performance of the fewest-switching and Landau-Zener surface-hopping algorithms for the photodissociation of phenol is very similar. The populations of the adiabatic S1 and S2 states are found to exhibit fast oscillations which reflect nonadiabatic electronic transitions driven by coherent dynamics in the OH stretching mode. These electronic population oscillations are qualitatively reproduced by both TSH algorithms.

We present a computational study of sub-picosecond nonadiabatic dynamics in a rhenium complex coupled electronically to a tryptophan (Trp) side chain of Pseudomonas aeruginosa azurin, a prototypical protein used in the study of electron transfer in proteins. To gain a comprehensive understanding of the photoinduced processes in this system, we have carried out vertical excitation calculations at the TDDFT level of theory as well as nonadiabatic dynamics simulations using the surface hopping including arbitrary couplings (SHARC) method coupled to potential energy surfaces represented with a linear vibronic coupling model. The results show that the initial photoexcitation populates both singlet metal-to-ligand charge transfer (MLCT) and singlet charge-separated (CS) states, where in the latter an electron was transferred from the Trp amino acid to the complex. Subsequently, a complex mechanism of simultaneous intersystem crossing and electron transfer leads to the sub-picosecond population of triplet MLCT and triplet CS states. These results confirm the assignment of the sub-ps time constants of previous experimental studies and constitute the first computational evidence for the ultrafast formation of the charge-separated states in Re-sensitized azurin.

Interaction between beta-carboline-3-carboxylic acid N-methylamide, betaCMAM, and nucleobases, nucleosides and nucleotides is studied in the ground state with UV-visible, (1)H NMR and (31)P NMR spectroscopies and in the first excited state, with steady-state and time-resolved fluorescence spectroscopy. Job plots show a predominant 1:1 interaction in both electronic states. Association constants are estimated from changes in the absorption spectra, and show that the strongest interaction is produced with the nucleosides: 2'-deoxyadenosine (dAdo) and thymidine (Thd), and with the mononucleotides: 2'-deoxycytidine 5'- monophosphate (5'-dCMP) and uridine 5'- monophosphate (5'-UMP). These results are corroborated by the upfield shifts of two (1)H NMR resonances of the betaCMAM indole group. The (31)P NMR resonance of nucleotides is shifted downfield, suggesting the presence of electrostatic or hydrogen bond interaction with betaCMAM. In the first electronic singlet excited state, static and dynamic quenching of betaCMAM emission is achieved upon addition of nucleobases, nucleosides and nucleotides. This has been analysed using Stern-Volmer kinetics.

Long time simulations, up to 100 ns, have been performed for the fragmentation of Kr7+ clusters after electron impact ionization. They rely on DIM approaches and hybrid non-adiabatic dynamics combining mean field and decoherence driven either by Tully fewest switches (TFS) algorithm or through electronic amplitude (AMP) calculations. With both methods, for the first time, when the initial electronic excited state belongs to group II correlating to P1/2 atomic ions, the fragmentation ratio in mainly monomer and dimer ions agrees very well with known experimental results. A complex non-adiabatic dynamics is found where initial neutral monomer evaporations due to gradual deexcitation over electronic states of group II are followed by a non-adiabatic transition across a wide energy gap of the spin-orbit origin to electronic states of group I. The resulting excess of kinetic energy causes the final fragmentation of charged intermediate fragments to stable ionic monomers or dimers. Characteristic times of these processes have been estimated. The kinetic energy distribution of the neutral and ionic monomers (the dominating final fragments) has been analyzed in detail. Interestingly they exhibit some signature of the initial excited electronic state which could allow for an experimental identification.

Biotites from the Eastern desert of Egypt are the subject of the present study. Mossbauer effect, X-ray diffraction and Chemical analysis were done. A strong electronic exchange interaction state was observed between neighbouring M1 and M2 positions. Correlations between the results obtained from different techniques are given on the basis of the electronic and structure characteristics of Biotite.

Assemblies of four oligophenylenevinylene moieties arising from a calix[4]arene core, i.e., calix[4]oligophenylenevinylenes, have been prepared by Heck-type cross-coupling reactions of styrene derivatives with a tetraiodinated cone-calix[4]arene precursor. Photophysical studies in solution have revealed that there are electronic ground state interactions between the covalently bonded OPV moieties. The absorption spectra of the calix[4]oligophenylenevinylenes are significantly different from those obtained by summing the spectra of four model units and their emission is red-shifted when compared to the corresponding model compounds. Electrochemical studies have shown that the redox processes of the four OPV subunits do not take place at the same potentials indicating also a strong electronic interaction among them in the calix[4]oligophenylenevinylenes.

In this article, the theoretical photoionization spectroscopy of the aziridine (C2H5N) molecule is investigated. To start with, we have optimized the geometry of this molecule at the neutral electronic ground state at the density functional theory/augmented correlation-consistent polarized valence triple zeta level of theory using the G09 program. The electronic structure calculations were restricted to the first six low-lying electronic states in order to account for the experimental photoelectron spectrum of the C2H5N molecule. The first six low-lying electronic states (X̃2A', Ã2A', B̃2A″, C̃2A″, D̃2A', and Ẽ2A') of the potential energy surfaces (PESs) are calculated by both equation of motion-ionization potential-coupled cluster singles and doubles and multi-configuration quasi-degenerate perturbation theory abinitio quantum chemistry methods along the dimensionless normal displacement coordinates in which multiple conical intersections were established among the considered electronic states. A (6 × 6) model vibronic Hamiltonian is constructed on a diabatic electronic basis, using the symmetry selection rules and Taylor series expansion. The Cs symmetry point group of the aziridine molecule leads to electronic states symmetry of either A' or A″, and these states are close in energy, due to which the same symmetry electronic states avoid each other. To get a smooth diabatic PES, a fourfold diabatization scheme is used, which is implemented in the General Atomic and Molecular Electronic Structure Systems suite of programs. All the parameters used in the diabatic vibronic coupling model Hamiltonian are calculated in terms of the normal modes of vibrational coordinates. Finally, the vibronic model Hamiltonian constructed for the coupled six electronic states is used to solve both time-independent and time-dependent Schrödinger equations using the multi-configuration time-dependent Hartree program module to obtain the dynamical observables. The theoretical vibronic band structure is found to be in good accord with the available experimental results.

Covalent functionalization of graphene oxide (GO) with boron dipyrromethenes (BODIPYs) was achieved through a facile synthesis, affording two different GO-BODIPY conjugates where the main difference lies in the nature of the spacer and the type of bonds between the two components. The use of a long but flexible spacer afforded strong electronic GO-BODIPY interactions in the ground state. This drastically altered the light absorption of the BODIPY structure and impeded its selective excitation. In contrast, the utilisation of a short, but rigid spacer based on boronic esters resulted in a perpendicular geometry of the phenyl boronic acid BODIPY (PBA-BODIPY) with respect to the GO plane, which enables only minor electronic GO-BODIPY interactions in the ground state. In this case, selective excitation of PBA-BODIPY was easily achieved, allowing to investigate the excited state interactions. A quantitative ultrafast energy transfer from PBA-BODIPY to GO was observed. Furthermore, due to the reversible dynamic nature of the covalent GO-PBA-BODIPY linkage, some PBA-BODIPY is free in solution and, hence, not quenched from GO. This resulted in a weak, but detectable fluorescence from the PBA-BODIPY that will allow to exploit GO-PBA-BODIPY for slow release and imaging purposes.

Boson Subsidiary Solver (BoSS) v1.1

We present an extension of the combined density functional theory (DFT) and multireference configuration interaction (MRCI) method (DFT/MRCI) [S. Grimme and M. Waletzke, J. Chem. Phys. 111, 5645 (1999)] for the calculation of core-excited states based on the core-valence separation (CVS) approximation. The resulting method, CVS-DFT/MRCI, is validated via the simulation of the K-edge X-ray absorption spectra of 40 organic chromophores, amino acids, and nucleobases, ranging in size from CO2 to tryptophan. Overall, the CVS-DFT/MRCI method is found to yield accurate X-ray absorption spectra (XAS), with consistent errors in peak positions of ∼2.5-3.5 eV. Additionally, we show that the CVS-DFT/MRCI method may be employed to simulate XAS from valence excited states and compare the simulated spectra to those computed using the established wave function-based approaches [ADC(2) and ADC(2)x]. In general, each of the methods yields excited state XAS spectra in qualitative and often quantitative agreement. In the instances where the methods differ, the CVS-DFT/MRCI simulations predict intensity for transitions for which the underlying electronic states are characterized by doubly excited configurations relative to the ground state configuration. Here, we aim to demonstrate that the CVS-DFT/MRCI approach occupies a specific niche among numerous other electronic structure methods in this area, offering the ability to treat initial states of arbitrary electronic character while maintaining a low computational cost and comparatively black box usage.

The H-atom photodissociationreaction from the pyridinyl radical (C5H5NH) via the low-lying πσ* excited electronic state is investigated by nonadiabatic time-dependent quantum wave-packet dynamics calculations. A model comprising three electronic states and three nuclear coordinates has been constructed using ab initio multi-configurational self-consistent-field and multi-reference perturbation theory methods. Two conical intersections among the three lowest electronic states have been characterized in the framework of the linear vibronic-coupling model. Time-dependent wave-packet simulations have been performed using the multi-configuration time-dependent Hartree method. The population dynamics of the diabatic and adiabatic electronic states and the time-dependent dissociation behavior are analyzed for various vibrational initial conditions. The results provide detailed mechanistic insight into the photoinduced H-atom dissociation process from a hypervalent aromatic radical and show that an efficient dissociationreaction through two conical intersections is possible.

In this paper we develop a “diatomic in molecules semiempirical ligand field” (DIMSELF) method to calculate ground and excited many-body potential energy surfaces for an arbitrary transition metal ion in an arbitrary complex system. This method is not restricted to a high-symmetry environment and is meant to be inexpensive and suitable for nonadiabatic excited states dynamics on-the-fly. Within the approximations employed, the method includes full CI (configuration interaction) and SO (spin-orbit) interactions, essential to the description of nonradiative transitions such as those of myoglobin in the presence of carbon monoxide. We test our method against high level ab initio calculations for a simple model system of myoglobin’s heme pocket. Finally, we discuss our results and compare with previous calculations in the literature. Transition metal complexes play a fundamental role in many technological and biological areas. They act as catalysts in the oil industry during the processes of cracking and reforming, they are also fundamental for oxygen transport in blood, and they are key to plant respiration. Some of these processes can be well understood without the need to include the small contribution of spin-orbit (SO) interaction which, for the most part, is of the order of the error one performs in ab initio calculations of these kind of systems. In some cases, however, nonradiative transitions occur between states with different spins. Of particular interest are heme proteins, a biologically important group of molecules that have a unique common active site: an iron-protoporphyrin-IX complex, where changes in spin state can be an integral part of the protein function. One of the most striking biological manifestations of this modulation is the binding of molecular oxygen and carbon monoxide (CO) 1-9 to the five-coordinated ferrous heme site of globins. Another wellstudied example is the situation of several spin changes in the enzymatic activation cycles of cytochromes P450. These transitions are solely due to SO coupling and are otherwise forbidden. Ab initio calculations are performed within the framework of Hund’s Case A and hence assume that S, the total spin of the system, is a good quantum number. Spin-orbit coupling matrix elements could then be added, and rediagonalization of the Hamiltonian matrix would provide us with the spin coupled eigenstates of the system. Obtaining several electronic excited states for a given spin multiplicity is complex, and for mediumsized systems only configuration interaction for single excitations (CIS) is affordable. However, a more complete description of excited states might be required for the study of dynamics. For large systems, where the environment can be introduced by mixing quantum chemistry with molecular mechanics, electronically excited states are rarely computationally accessible and only the fundamental ground state for each spin multiplicity might be computed. For nonsymmetric systems, even at the density functional theory (DFT) level of theory, several attempts with different initial guesses should be considered in order to achieve the true ground state. The computational effort is drastically increased when several nuclear configurations are required for a complete study of the dynamics, and calculations on-the-fly, including excited states and SO coupling, are simply out of the question. Therefore, a semiempirical approach that includes excited states and SO coupling is very desirable. The method we develop in this paper is a generalization of Gerloch’s 10 cellular AOM (angular overlap model) version of ligand field theory, combined with a semiempirical version of Ellison’s 11-13 DIM (diatomics in molecules). Neither ligand field theory nor the semiempirical version of DIM are exact ab initio methods; not all the parameters can be obtained by analytical methods and they ought to be fitted either to experimental data or other calculations. On the other hand, once these parameters are known, fast computation of ground- and excited-state potentials can be performed without having to recalculate wave functions and their matrix elements. We test this method against a simplified model of the heme

Catalytic activity of thermal CO oxidation was studied for monatomic-layered platinum cluster disks, Pt30, bonded to the (111) surface of a silicon substrate. Temperature-programmed desorption (TPD) measurements were repeated for a given cluster sample with a systematic change in the reactant amounts supplied, and the peaks observed in the TPD spectra were deconvoluted so as to obtain probabilities of individual reactions. It was concluded that this system possesses an ability of low-temperature reductive activation of oxygen molecules, which is one of the critical steps in the CO oxidation. This high performance is explained in terms of negative charges accumulated at a sub-nano interface between the cluster disk and the silicon substrate surface as a result of their strong electronic interaction.