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Author ORCID ID is 0000000247988947
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Conical intersections play a critical role in excitedstate dynamics of polyatomic molecules because they govern the reaction pathways of many nonadiabatic processes. However, ultrafast probes have lacked sufficient spatial resolution to image wavepacket trajectories through these intersections directly. Here in this paper, we present the simultaneous experimental characterization of onephoton and twophoton excitation channels in isolated CF _{3}I molecules using ultrafast gasphase electron diffraction. In the twophoton channel, we have mapped out the realspace trajectories of a coherent nuclear wave packet, which bifurcates onto two potential energy surfaces when passing through a conical intersection. In the onephoton channel, we havemore »Cited by 1Full Text Available

Here, the spinrestricted ensemblereferenced KohnSham (REKS) method is based on an ensemble representation of the density and is capable of correctly describing the nondynamic electron correlation stemming from (near)degeneracy of several electronic configurations. The existing REKS methodology describes systems with two electrons in two fractionally occupied orbitals. In this work, the REKS methodology is extended to treat systems with four fractionally occupied orbitals accommodating four electrons and selfconsistent implementation of the REKS(4,4) method with simultaneous optimization of the orbitals and their fractional occupation numbers is reported. The new method is applied to a number of molecular systems where simultaneous dissociationmore »Cited by 3Full Text Available

We recently outlined an efficient multitiered parallel ab initio excitonic framework that utilizes time dependent density functional theory (TDDFT) to calculate ground and excited state energies and gradients of large supramolecular complexes in atomistic detail – enabling us to undertake nonadiabatic simulations which explicitly account for the coupled anharmonic vibrational motion of all the constituent atoms in a supramolecular system. Here we apply that framework to the 27 coupled bacteriochlorophylla chromophores which make up the LH2 complex, using it to compute an onthefly nonadiabatic surfacehopping (SH) trajectory of electronically excited LH2. Part one of this article is focussed on calibratingmore »Cited by 8Full Text Available

Here, we present a reduced scaling formulation of the state specific complete active space secondorder perturbation method (CASPT2) requiring O( N ^{4}) operations and O( N ^{2}) memory for a fixed active space, where N is proportional to system size. Motivated by the properties of the Kronecker sum, we introduce the supporting subspace technique (SST), which decomposes the CASPT2 linear equations into two parts: a singlereference MP2 energy term using dressed orbitals, plus a reduced linear system with dimension scaling as O( N ^{2}). Together with Laplace quadrature, the SST allows us to reformulate CASPT2 using a MP2 energy computationmore »

Hydrogen bonds are fundamental to biological systems and are regularly found in networks implicated in folding, molecular recognition, catalysis, and allostery. Given their ubiquity, we asked the fundamental questions of whether, and to what extent, hydrogen bonds within networks are structurally coupled. To address these questions, we turned to three protein systems, two variants of ketosteroid isomerase and one of photoactive yellow protein. We perturbed their hydrogen bond networks via a combination of sitedirected mutagenesis and unnatural amino acid substitution, and we used ^{1}H NMR and highresolution Xray crystallography to determine the effects of these perturbations on the lengths ofmore »

Here, we present the rankreduced full configuration interaction (RRFCI) method, a variational approach for the calculation of extremely large full configuration interaction (FCI) wave functions. In this report, we show that RRFCI can provide ground state singlet and triplet energies within kcal/mol accuracy of full CI (FCI) with computational effort scaling as the square root of the number of determinants in the CI space (compared to conventional FCI methods which scale linearly with the number of determinants). Fast graphical processing unit (GPU) accelerated projected σ = Hc matrix–vector product formation enables calculations with configuration spaces as large as 30 electronsmore »

The excited state nonadiabatic dynamics of the smallest polyene, trans 1,3butadiene (BD), has long been the subject of controversy due to its strong coupling, ultrafast time scales and the difficulties that theory faces in describing the relevant electronic states in a balanced fashion. Here we apply Ab Initio Multiple Spawning (AIMS) using stateaveraged complete active space multistate second order perturbation theory [SA3CAS(4/4)MSPT2] which describes both static and dynamic electron correlation effects, providing a balanced description of both the initially prepared bright 1 ^{1}B _{u} (ππ*) state and nonadiabatically coupled dark 2 ^{1}A _{g} state of BD. Importantly, AIMS allows formore »

The ultrafast excited state dynamics of the smallest polyene, trans1,3butadiene, were studied by femtosecond timeresolved photoelectronphotoion coincidence (TRPEPICO) spectroscopy. The evolution of the excited state wavepacket, created by pumping the bright ^{1}B _{u} (ππ*) electronic state at its origin of 216 nm, is projected via one and twophoton ionization at 267 nm onto several ionization continua. The results are interpreted in terms of Koopmans’ correlations and FranckCondon factors for the excited and cationic states involved. The known predissociative character of the cation excited states is utilized to assign photoelectron bands to specific continua using TRPEPICO spectroscopy. This permits us tomore »Cited by 2

Here, the Born–Oppenheimer approximation underlies much of chemical simulation and provides the framework defining the potential energy surfaces that are used for much of our pictorial understanding of chemical phenomena. However, this approximation breaks down when the dynamics of molecules in excited electronic states are considered. Describing dynamics when the Born–Oppenheimer approximation breaks down requires a quantum mechanical description of the nuclei. Chemical reaction dynamics on excited electronic states is critical for many applications in renewable energy, chemical synthesis, and bioimaging. Furthermore, it is necessary in order to connect with many ultrafast pump–probe spectroscopic experiments. In this review, we providemore »Cited by 6
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